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//===- SROA.cpp - Scalar Replacement Of Aggregates ------------------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
/// \file
/// This transformation implements the well known scalar replacement of
/// aggregates transformation. It tries to identify promotable elements of an
/// aggregate alloca, and promote them to registers. It will also try to
/// convert uses of an element (or set of elements) of an alloca into a vector
/// or bitfield-style integer scalar if appropriate.
///
/// It works to do this with minimal slicing of the alloca so that regions
/// which are merely transferred in and out of external memory remain unchanged
/// and are not decomposed to scalar code.
///
/// Because this also performs alloca promotion, it can be thought of as also
/// serving the purpose of SSA formation. The algorithm iterates on the
/// function until all opportunities for promotion have been realized.
///
//===----------------------------------------------------------------------===//
#include "llvm/Transforms/Scalar/SROA.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Analysis/AssumptionCache.h"
#include "llvm/Analysis/GlobalsModRef.h"
#include "llvm/Analysis/Loads.h"
#include "llvm/Analysis/PtrUseVisitor.h"
#include "llvm/Analysis/ValueTracking.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/DIBuilder.h"
#include "llvm/IR/DataLayout.h"
#include "llvm/IR/DebugInfo.h"
#include "llvm/IR/DerivedTypes.h"
#include "llvm/IR/IRBuilder.h"
#include "llvm/IR/InstVisitor.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/IR/LLVMContext.h"
#include "llvm/IR/Operator.h"
#include "llvm/Pass.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/MathExtras.h"
#include "llvm/Support/TimeValue.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Transforms/Scalar.h"
#include "llvm/Transforms/Utils/Local.h"
#include "llvm/Transforms/Utils/PromoteMemToReg.h"
#ifndef NDEBUG
// We only use this for a debug check.
#include <random>
#endif
using namespace llvm;
using namespace llvm::sroa;
#define DEBUG_TYPE "sroa"
STATISTIC(NumAllocasAnalyzed, "Number of allocas analyzed for replacement");
STATISTIC(NumAllocaPartitions, "Number of alloca partitions formed");
STATISTIC(MaxPartitionsPerAlloca, "Maximum number of partitions per alloca");
STATISTIC(NumAllocaPartitionUses, "Number of alloca partition uses rewritten");
STATISTIC(MaxUsesPerAllocaPartition, "Maximum number of uses of a partition");
STATISTIC(NumNewAllocas, "Number of new, smaller allocas introduced");
STATISTIC(NumPromoted, "Number of allocas promoted to SSA values");
STATISTIC(NumLoadsSpeculated, "Number of loads speculated to allow promotion");
STATISTIC(NumDeleted, "Number of instructions deleted");
STATISTIC(NumVectorized, "Number of vectorized aggregates");
/// Hidden option to enable randomly shuffling the slices to help uncover
/// instability in their order.
static cl::opt<bool> SROARandomShuffleSlices("sroa-random-shuffle-slices",
cl::init(false), cl::Hidden);
/// Hidden option to experiment with completely strict handling of inbounds
/// GEPs.
static cl::opt<bool> SROAStrictInbounds("sroa-strict-inbounds", cl::init(false),
cl::Hidden);
namespace {
/// \brief A custom IRBuilder inserter which prefixes all names, but only in
/// Assert builds.
class IRBuilderPrefixedInserter : public IRBuilderDefaultInserter {
std::string Prefix;
const Twine getNameWithPrefix(const Twine &Name) const {
return Name.isTriviallyEmpty() ? Name : Prefix + Name;
}
public:
void SetNamePrefix(const Twine &P) { Prefix = P.str(); }
protected:
void InsertHelper(Instruction *I, const Twine &Name, BasicBlock *BB,
BasicBlock::iterator InsertPt) const {
IRBuilderDefaultInserter::InsertHelper(I, getNameWithPrefix(Name), BB,
InsertPt);
}
};
/// \brief Provide a typedef for IRBuilder that drops names in release builds.
using IRBuilderTy = llvm::IRBuilder<ConstantFolder, IRBuilderPrefixedInserter>;
}
namespace {
/// \brief A used slice of an alloca.
///
/// This structure represents a slice of an alloca used by some instruction. It
/// stores both the begin and end offsets of this use, a pointer to the use
/// itself, and a flag indicating whether we can classify the use as splittable
/// or not when forming partitions of the alloca.
class Slice {
/// \brief The beginning offset of the range.
uint64_t BeginOffset;
/// \brief The ending offset, not included in the range.
uint64_t EndOffset;
/// \brief Storage for both the use of this slice and whether it can be
/// split.
PointerIntPair<Use *, 1, bool> UseAndIsSplittable;
public:
Slice() : BeginOffset(), EndOffset() {}
Slice(uint64_t BeginOffset, uint64_t EndOffset, Use *U, bool IsSplittable)
: BeginOffset(BeginOffset), EndOffset(EndOffset),
UseAndIsSplittable(U, IsSplittable) {}
uint64_t beginOffset() const { return BeginOffset; }
uint64_t endOffset() const { return EndOffset; }
bool isSplittable() const { return UseAndIsSplittable.getInt(); }
void makeUnsplittable() { UseAndIsSplittable.setInt(false); }
Use *getUse() const { return UseAndIsSplittable.getPointer(); }
bool isDead() const { return getUse() == nullptr; }
void kill() { UseAndIsSplittable.setPointer(nullptr); }
/// \brief Support for ordering ranges.
///
/// This provides an ordering over ranges such that start offsets are
/// always increasing, and within equal start offsets, the end offsets are
/// decreasing. Thus the spanning range comes first in a cluster with the
/// same start position.
bool operator<(const Slice &RHS) const {
if (beginOffset() < RHS.beginOffset())
return true;
if (beginOffset() > RHS.beginOffset())
return false;
if (isSplittable() != RHS.isSplittable())
return !isSplittable();
if (endOffset() > RHS.endOffset())
return true;
return false;
}
/// \brief Support comparison with a single offset to allow binary searches.
friend LLVM_ATTRIBUTE_UNUSED bool operator<(const Slice &LHS,
uint64_t RHSOffset) {
return LHS.beginOffset() < RHSOffset;
}
friend LLVM_ATTRIBUTE_UNUSED bool operator<(uint64_t LHSOffset,
const Slice &RHS) {
return LHSOffset < RHS.beginOffset();
}
bool operator==(const Slice &RHS) const {
return isSplittable() == RHS.isSplittable() &&
beginOffset() == RHS.beginOffset() && endOffset() == RHS.endOffset();
}
bool operator!=(const Slice &RHS) const { return !operator==(RHS); }
};
} // end anonymous namespace
namespace llvm {
template <typename T> struct isPodLike;
template <> struct isPodLike<Slice> { static const bool value = true; };
}
/// \brief Representation of the alloca slices.
///
/// This class represents the slices of an alloca which are formed by its
/// various uses. If a pointer escapes, we can't fully build a representation
/// for the slices used and we reflect that in this structure. The uses are
/// stored, sorted by increasing beginning offset and with unsplittable slices
/// starting at a particular offset before splittable slices.
class llvm::sroa::AllocaSlices {
public:
/// \brief Construct the slices of a particular alloca.
AllocaSlices(const DataLayout &DL, AllocaInst &AI);
/// \brief Test whether a pointer to the allocation escapes our analysis.
///
/// If this is true, the slices are never fully built and should be
/// ignored.
bool isEscaped() const { return PointerEscapingInstr; }
/// \brief Support for iterating over the slices.
/// @{
typedef SmallVectorImpl<Slice>::iterator iterator;
typedef iterator_range<iterator> range;
iterator begin() { return Slices.begin(); }
iterator end() { return Slices.end(); }
typedef SmallVectorImpl<Slice>::const_iterator const_iterator;
typedef iterator_range<const_iterator> const_range;
const_iterator begin() const { return Slices.begin(); }
const_iterator end() const { return Slices.end(); }
/// @}
/// \brief Erase a range of slices.
void erase(iterator Start, iterator Stop) { Slices.erase(Start, Stop); }
/// \brief Insert new slices for this alloca.
///
/// This moves the slices into the alloca's slices collection, and re-sorts
/// everything so that the usual ordering properties of the alloca's slices
/// hold.
void insert(ArrayRef<Slice> NewSlices) {
int OldSize = Slices.size();
Slices.append(NewSlices.begin(), NewSlices.end());
auto SliceI = Slices.begin() + OldSize;
std::sort(SliceI, Slices.end());
std::inplace_merge(Slices.begin(), SliceI, Slices.end());
}
// Forward declare the iterator and range accessor for walking the
// partitions.
class partition_iterator;
iterator_range<partition_iterator> partitions();
/// \brief Access the dead users for this alloca.
ArrayRef<Instruction *> getDeadUsers() const { return DeadUsers; }
/// \brief Access the dead operands referring to this alloca.
///
/// These are operands which have cannot actually be used to refer to the
/// alloca as they are outside its range and the user doesn't correct for
/// that. These mostly consist of PHI node inputs and the like which we just
/// need to replace with undef.
ArrayRef<Use *> getDeadOperands() const { return DeadOperands; }
#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
void print(raw_ostream &OS, const_iterator I, StringRef Indent = " ") const;
void printSlice(raw_ostream &OS, const_iterator I,
StringRef Indent = " ") const;
void printUse(raw_ostream &OS, const_iterator I,
StringRef Indent = " ") const;
void print(raw_ostream &OS) const;
void dump(const_iterator I) const;
void dump() const;
#endif
private:
template <typename DerivedT, typename RetT = void> class BuilderBase;
class SliceBuilder;
friend class AllocaSlices::SliceBuilder;
#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
/// \brief Handle to alloca instruction to simplify method interfaces.
AllocaInst &AI;
#endif
/// \brief The instruction responsible for this alloca not having a known set
/// of slices.
///
/// When an instruction (potentially) escapes the pointer to the alloca, we
/// store a pointer to that here and abort trying to form slices of the
/// alloca. This will be null if the alloca slices are analyzed successfully.
Instruction *PointerEscapingInstr;
/// \brief The slices of the alloca.
///
/// We store a vector of the slices formed by uses of the alloca here. This
/// vector is sorted by increasing begin offset, and then the unsplittable
/// slices before the splittable ones. See the Slice inner class for more
/// details.
SmallVector<Slice, 8> Slices;
/// \brief Instructions which will become dead if we rewrite the alloca.
///
/// Note that these are not separated by slice. This is because we expect an
/// alloca to be completely rewritten or not rewritten at all. If rewritten,
/// all these instructions can simply be removed and replaced with undef as
/// they come from outside of the allocated space.
SmallVector<Instruction *, 8> DeadUsers;
/// \brief Operands which will become dead if we rewrite the alloca.
///
/// These are operands that in their particular use can be replaced with
/// undef when we rewrite the alloca. These show up in out-of-bounds inputs
/// to PHI nodes and the like. They aren't entirely dead (there might be
/// a GEP back into the bounds using it elsewhere) and nor is the PHI, but we
/// want to swap this particular input for undef to simplify the use lists of
/// the alloca.
SmallVector<Use *, 8> DeadOperands;
};
/// \brief A partition of the slices.
///
/// An ephemeral representation for a range of slices which can be viewed as
/// a partition of the alloca. This range represents a span of the alloca's
/// memory which cannot be split, and provides access to all of the slices
/// overlapping some part of the partition.
///
/// Objects of this type are produced by traversing the alloca's slices, but
/// are only ephemeral and not persistent.
class llvm::sroa::Partition {
private:
friend class AllocaSlices;
friend class AllocaSlices::partition_iterator;
typedef AllocaSlices::iterator iterator;
/// \brief The beginning and ending offsets of the alloca for this
/// partition.
uint64_t BeginOffset, EndOffset;
/// \brief The start end end iterators of this partition.
iterator SI, SJ;
/// \brief A collection of split slice tails overlapping the partition.
SmallVector<Slice *, 4> SplitTails;
/// \brief Raw constructor builds an empty partition starting and ending at
/// the given iterator.
Partition(iterator SI) : SI(SI), SJ(SI) {}
public:
/// \brief The start offset of this partition.
///
/// All of the contained slices start at or after this offset.
uint64_t beginOffset() const { return BeginOffset; }
/// \brief The end offset of this partition.
///
/// All of the contained slices end at or before this offset.
uint64_t endOffset() const { return EndOffset; }
/// \brief The size of the partition.
///
/// Note that this can never be zero.
uint64_t size() const {
assert(BeginOffset < EndOffset && "Partitions must span some bytes!");
return EndOffset - BeginOffset;
}
/// \brief Test whether this partition contains no slices, and merely spans
/// a region occupied by split slices.
bool empty() const { return SI == SJ; }
/// \name Iterate slices that start within the partition.
/// These may be splittable or unsplittable. They have a begin offset >= the
/// partition begin offset.
/// @{
// FIXME: We should probably define a "concat_iterator" helper and use that
// to stitch together pointee_iterators over the split tails and the
// contiguous iterators of the partition. That would give a much nicer
// interface here. We could then additionally expose filtered iterators for
// split, unsplit, and unsplittable splices based on the usage patterns.
iterator begin() const { return SI; }
iterator end() const { return SJ; }
/// @}
/// \brief Get the sequence of split slice tails.
///
/// These tails are of slices which start before this partition but are
/// split and overlap into the partition. We accumulate these while forming
/// partitions.
ArrayRef<Slice *> splitSliceTails() const { return SplitTails; }
};
/// \brief An iterator over partitions of the alloca's slices.
///
/// This iterator implements the core algorithm for partitioning the alloca's
/// slices. It is a forward iterator as we don't support backtracking for
/// efficiency reasons, and re-use a single storage area to maintain the
/// current set of split slices.
///
/// It is templated on the slice iterator type to use so that it can operate
/// with either const or non-const slice iterators.
class AllocaSlices::partition_iterator
: public iterator_facade_base<partition_iterator, std::forward_iterator_tag,
Partition> {
friend class AllocaSlices;
/// \brief Most of the state for walking the partitions is held in a class
/// with a nice interface for examining them.
Partition P;
/// \brief We need to keep the end of the slices to know when to stop.
AllocaSlices::iterator SE;
/// \brief We also need to keep track of the maximum split end offset seen.
/// FIXME: Do we really?
uint64_t MaxSplitSliceEndOffset;
/// \brief Sets the partition to be empty at given iterator, and sets the
/// end iterator.
partition_iterator(AllocaSlices::iterator SI, AllocaSlices::iterator SE)
: P(SI), SE(SE), MaxSplitSliceEndOffset(0) {
// If not already at the end, advance our state to form the initial
// partition.
if (SI != SE)
advance();
}
/// \brief Advance the iterator to the next partition.
///
/// Requires that the iterator not be at the end of the slices.
void advance() {
assert((P.SI != SE || !P.SplitTails.empty()) &&
"Cannot advance past the end of the slices!");
// Clear out any split uses which have ended.
if (!P.SplitTails.empty()) {
if (P.EndOffset >= MaxSplitSliceEndOffset) {
// If we've finished all splits, this is easy.
P.SplitTails.clear();
MaxSplitSliceEndOffset = 0;
} else {
// Remove the uses which have ended in the prior partition. This
// cannot change the max split slice end because we just checked that
// the prior partition ended prior to that max.
P.SplitTails.erase(
std::remove_if(
P.SplitTails.begin(), P.SplitTails.end(),
[&](Slice *S) { return S->endOffset() <= P.EndOffset; }),
P.SplitTails.end());
assert(std::any_of(P.SplitTails.begin(), P.SplitTails.end(),
[&](Slice *S) {
return S->endOffset() == MaxSplitSliceEndOffset;
}) &&
"Could not find the current max split slice offset!");
assert(std::all_of(P.SplitTails.begin(), P.SplitTails.end(),
[&](Slice *S) {
return S->endOffset() <= MaxSplitSliceEndOffset;
}) &&
"Max split slice end offset is not actually the max!");
}
}
// If P.SI is already at the end, then we've cleared the split tail and
// now have an end iterator.
if (P.SI == SE) {
assert(P.SplitTails.empty() && "Failed to clear the split slices!");
return;
}
// If we had a non-empty partition previously, set up the state for
// subsequent partitions.
if (P.SI != P.SJ) {
// Accumulate all the splittable slices which started in the old
// partition into the split list.
for (Slice &S : P)
if (S.isSplittable() && S.endOffset() > P.EndOffset) {
P.SplitTails.push_back(&S);
MaxSplitSliceEndOffset =
std::max(S.endOffset(), MaxSplitSliceEndOffset);
}
// Start from the end of the previous partition.
P.SI = P.SJ;
// If P.SI is now at the end, we at most have a tail of split slices.
if (P.SI == SE) {
P.BeginOffset = P.EndOffset;
P.EndOffset = MaxSplitSliceEndOffset;
return;
}
// If the we have split slices and the next slice is after a gap and is
// not splittable immediately form an empty partition for the split
// slices up until the next slice begins.
if (!P.SplitTails.empty() && P.SI->beginOffset() != P.EndOffset &&
!P.SI->isSplittable()) {
P.BeginOffset = P.EndOffset;
P.EndOffset = P.SI->beginOffset();
return;
}
}
// OK, we need to consume new slices. Set the end offset based on the
// current slice, and step SJ past it. The beginning offset of the
// partition is the beginning offset of the next slice unless we have
// pre-existing split slices that are continuing, in which case we begin
// at the prior end offset.
P.BeginOffset = P.SplitTails.empty() ? P.SI->beginOffset() : P.EndOffset;
P.EndOffset = P.SI->endOffset();
++P.SJ;
// There are two strategies to form a partition based on whether the
// partition starts with an unsplittable slice or a splittable slice.
if (!P.SI->isSplittable()) {
// When we're forming an unsplittable region, it must always start at
// the first slice and will extend through its end.
assert(P.BeginOffset == P.SI->beginOffset());
// Form a partition including all of the overlapping slices with this
// unsplittable slice.
while (P.SJ != SE && P.SJ->beginOffset() < P.EndOffset) {
if (!P.SJ->isSplittable())
P.EndOffset = std::max(P.EndOffset, P.SJ->endOffset());
++P.SJ;
}
// We have a partition across a set of overlapping unsplittable
// partitions.
return;
}
// If we're starting with a splittable slice, then we need to form
// a synthetic partition spanning it and any other overlapping splittable
// splices.
assert(P.SI->isSplittable() && "Forming a splittable partition!");
// Collect all of the overlapping splittable slices.
while (P.SJ != SE && P.SJ->beginOffset() < P.EndOffset &&
P.SJ->isSplittable()) {
P.EndOffset = std::max(P.EndOffset, P.SJ->endOffset());
++P.SJ;
}
// Back upiP.EndOffset if we ended the span early when encountering an
// unsplittable slice. This synthesizes the early end offset of
// a partition spanning only splittable slices.
if (P.SJ != SE && P.SJ->beginOffset() < P.EndOffset) {
assert(!P.SJ->isSplittable());
P.EndOffset = P.SJ->beginOffset();
}
}
public:
bool operator==(const partition_iterator &RHS) const {
assert(SE == RHS.SE &&
"End iterators don't match between compared partition iterators!");
// The observed positions of partitions is marked by the P.SI iterator and
// the emptiness of the split slices. The latter is only relevant when
// P.SI == SE, as the end iterator will additionally have an empty split
// slices list, but the prior may have the same P.SI and a tail of split
// slices.
if (P.SI == RHS.P.SI && P.SplitTails.empty() == RHS.P.SplitTails.empty()) {
assert(P.SJ == RHS.P.SJ &&
"Same set of slices formed two different sized partitions!");
assert(P.SplitTails.size() == RHS.P.SplitTails.size() &&
"Same slice position with differently sized non-empty split "
"slice tails!");
return true;
}
return false;
}
partition_iterator &operator++() {
advance();
return *this;
}
Partition &operator*() { return P; }
};
/// \brief A forward range over the partitions of the alloca's slices.
///
/// This accesses an iterator range over the partitions of the alloca's
/// slices. It computes these partitions on the fly based on the overlapping
/// offsets of the slices and the ability to split them. It will visit "empty"
/// partitions to cover regions of the alloca only accessed via split
/// slices.
iterator_range<AllocaSlices::partition_iterator> AllocaSlices::partitions() {
return make_range(partition_iterator(begin(), end()),
partition_iterator(end(), end()));
}
static Value *foldSelectInst(SelectInst &SI) {
// If the condition being selected on is a constant or the same value is
// being selected between, fold the select. Yes this does (rarely) happen
// early on.
if (ConstantInt *CI = dyn_cast<ConstantInt>(SI.getCondition()))
return SI.getOperand(1 + CI->isZero());
if (SI.getOperand(1) == SI.getOperand(2))
return SI.getOperand(1);
return nullptr;
}
/// \brief A helper that folds a PHI node or a select.
static Value *foldPHINodeOrSelectInst(Instruction &I) {
if (PHINode *PN = dyn_cast<PHINode>(&I)) {
// If PN merges together the same value, return that value.
return PN->hasConstantValue();
}
return foldSelectInst(cast<SelectInst>(I));
}
/// \brief Builder for the alloca slices.
///
/// This class builds a set of alloca slices by recursively visiting the uses
/// of an alloca and making a slice for each load and store at each offset.
class AllocaSlices::SliceBuilder : public PtrUseVisitor<SliceBuilder> {
friend class PtrUseVisitor<SliceBuilder>;
friend class InstVisitor<SliceBuilder>;
typedef PtrUseVisitor<SliceBuilder> Base;
const uint64_t AllocSize;
AllocaSlices &AS;
SmallDenseMap<Instruction *, unsigned> MemTransferSliceMap;
SmallDenseMap<Instruction *, uint64_t> PHIOrSelectSizes;
/// \brief Set to de-duplicate dead instructions found in the use walk.
SmallPtrSet<Instruction *, 4> VisitedDeadInsts;
public:
SliceBuilder(const DataLayout &DL, AllocaInst &AI, AllocaSlices &AS)
: PtrUseVisitor<SliceBuilder>(DL),
AllocSize(DL.getTypeAllocSize(AI.getAllocatedType())), AS(AS) {}
private:
void markAsDead(Instruction &I) {
if (VisitedDeadInsts.insert(&I).second)
AS.DeadUsers.push_back(&I);
}
void insertUse(Instruction &I, const APInt &Offset, uint64_t Size,
bool IsSplittable = false) {
// Completely skip uses which have a zero size or start either before or
// past the end of the allocation.
if (Size == 0 || Offset.uge(AllocSize)) {
DEBUG(dbgs() << "WARNING: Ignoring " << Size << " byte use @" << Offset
<< " which has zero size or starts outside of the "
<< AllocSize << " byte alloca:\n"
<< " alloca: " << AS.AI << "\n"
<< " use: " << I << "\n");
return markAsDead(I);
}
uint64_t BeginOffset = Offset.getZExtValue();
uint64_t EndOffset = BeginOffset + Size;
// Clamp the end offset to the end of the allocation. Note that this is
// formulated to handle even the case where "BeginOffset + Size" overflows.
// This may appear superficially to be something we could ignore entirely,
// but that is not so! There may be widened loads or PHI-node uses where
// some instructions are dead but not others. We can't completely ignore
// them, and so have to record at least the information here.
assert(AllocSize >= BeginOffset); // Established above.
if (Size > AllocSize - BeginOffset) {
DEBUG(dbgs() << "WARNING: Clamping a " << Size << " byte use @" << Offset
<< " to remain within the " << AllocSize << " byte alloca:\n"
<< " alloca: " << AS.AI << "\n"
<< " use: " << I << "\n");
EndOffset = AllocSize;
}
AS.Slices.push_back(Slice(BeginOffset, EndOffset, U, IsSplittable));
}
void visitBitCastInst(BitCastInst &BC) {
if (BC.use_empty())
return markAsDead(BC);
return Base::visitBitCastInst(BC);
}
void visitGetElementPtrInst(GetElementPtrInst &GEPI) {
if (GEPI.use_empty())
return markAsDead(GEPI);
if (SROAStrictInbounds && GEPI.isInBounds()) {
// FIXME: This is a manually un-factored variant of the basic code inside
// of GEPs with checking of the inbounds invariant specified in the
// langref in a very strict sense. If we ever want to enable
// SROAStrictInbounds, this code should be factored cleanly into
// PtrUseVisitor, but it is easier to experiment with SROAStrictInbounds
// by writing out the code here where we have the underlying allocation
// size readily available.
APInt GEPOffset = Offset;
const DataLayout &DL = GEPI.getModule()->getDataLayout();
for (gep_type_iterator GTI = gep_type_begin(GEPI),
GTE = gep_type_end(GEPI);
GTI != GTE; ++GTI) {
ConstantInt *OpC = dyn_cast<ConstantInt>(GTI.getOperand());
if (!OpC)
break;
// Handle a struct index, which adds its field offset to the pointer.
if (StructType *STy = dyn_cast<StructType>(*GTI)) {
unsigned ElementIdx = OpC->getZExtValue();
const StructLayout *SL = DL.getStructLayout(STy);
GEPOffset +=
APInt(Offset.getBitWidth(), SL->getElementOffset(ElementIdx));
} else {
// For array or vector indices, scale the index by the size of the
// type.
APInt Index = OpC->getValue().sextOrTrunc(Offset.getBitWidth());
GEPOffset += Index * APInt(Offset.getBitWidth(),
DL.getTypeAllocSize(GTI.getIndexedType()));
}
// If this index has computed an intermediate pointer which is not
// inbounds, then the result of the GEP is a poison value and we can
// delete it and all uses.
if (GEPOffset.ugt(AllocSize))
return markAsDead(GEPI);
}
}
return Base::visitGetElementPtrInst(GEPI);
}
void handleLoadOrStore(Type *Ty, Instruction &I, const APInt &Offset,
uint64_t Size, bool IsVolatile) {
// We allow splitting of non-volatile loads and stores where the type is an
// integer type. These may be used to implement 'memcpy' or other "transfer
// of bits" patterns.
bool IsSplittable = Ty->isIntegerTy() && !IsVolatile;
insertUse(I, Offset, Size, IsSplittable);
}
void visitLoadInst(LoadInst &LI) {
assert((!LI.isSimple() || LI.getType()->isSingleValueType()) &&
"All simple FCA loads should have been pre-split");
if (!IsOffsetKnown)
return PI.setAborted(&LI);
const DataLayout &DL = LI.getModule()->getDataLayout();
uint64_t Size = DL.getTypeStoreSize(LI.getType());
return handleLoadOrStore(LI.getType(), LI, Offset, Size, LI.isVolatile());
}
void visitStoreInst(StoreInst &SI) {
Value *ValOp = SI.getValueOperand();
if (ValOp == *U)
return PI.setEscapedAndAborted(&SI);
if (!IsOffsetKnown)
return PI.setAborted(&SI);
const DataLayout &DL = SI.getModule()->getDataLayout();
uint64_t Size = DL.getTypeStoreSize(ValOp->getType());
// If this memory access can be shown to *statically* extend outside the
// bounds of of the allocation, it's behavior is undefined, so simply
// ignore it. Note that this is more strict than the generic clamping
// behavior of insertUse. We also try to handle cases which might run the
// risk of overflow.
// FIXME: We should instead consider the pointer to have escaped if this
// function is being instrumented for addressing bugs or race conditions.
if (Size > AllocSize || Offset.ugt(AllocSize - Size)) {
DEBUG(dbgs() << "WARNING: Ignoring " << Size << " byte store @" << Offset
<< " which extends past the end of the " << AllocSize
<< " byte alloca:\n"
<< " alloca: " << AS.AI << "\n"
<< " use: " << SI << "\n");
return markAsDead(SI);
}
assert((!SI.isSimple() || ValOp->getType()->isSingleValueType()) &&
"All simple FCA stores should have been pre-split");
handleLoadOrStore(ValOp->getType(), SI, Offset, Size, SI.isVolatile());
}
void visitMemSetInst(MemSetInst &II) {
assert(II.getRawDest() == *U && "Pointer use is not the destination?");
ConstantInt *Length = dyn_cast<ConstantInt>(II.getLength());
if ((Length && Length->getValue() == 0) ||
(IsOffsetKnown && Offset.uge(AllocSize)))
// Zero-length mem transfer intrinsics can be ignored entirely.
return markAsDead(II);
if (!IsOffsetKnown)
return PI.setAborted(&II);
insertUse(II, Offset, Length ? Length->getLimitedValue()
: AllocSize - Offset.getLimitedValue(),
(bool)Length);
}
void visitMemTransferInst(MemTransferInst &II) {
ConstantInt *Length = dyn_cast<ConstantInt>(II.getLength());
if (Length && Length->getValue() == 0)
// Zero-length mem transfer intrinsics can be ignored entirely.
return markAsDead(II);
// Because we can visit these intrinsics twice, also check to see if the
// first time marked this instruction as dead. If so, skip it.
if (VisitedDeadInsts.count(&II))
return;
if (!IsOffsetKnown)
return PI.setAborted(&II);
// This side of the transfer is completely out-of-bounds, and so we can
// nuke the entire transfer. However, we also need to nuke the other side
// if already added to our partitions.
// FIXME: Yet another place we really should bypass this when
// instrumenting for ASan.
if (Offset.uge(AllocSize)) {
SmallDenseMap<Instruction *, unsigned>::iterator MTPI =
MemTransferSliceMap.find(&II);
if (MTPI != MemTransferSliceMap.end())
AS.Slices[MTPI->second].kill();
return markAsDead(II);
}
uint64_t RawOffset = Offset.getLimitedValue();
uint64_t Size = Length ? Length->getLimitedValue() : AllocSize - RawOffset;
// Check for the special case where the same exact value is used for both
// source and dest.
if (*U == II.getRawDest() && *U == II.getRawSource()) {
// For non-volatile transfers this is a no-op.
if (!II.isVolatile())
return markAsDead(II);
return insertUse(II, Offset, Size, /*IsSplittable=*/false);
}
// If we have seen both source and destination for a mem transfer, then
// they both point to the same alloca.
bool Inserted;
SmallDenseMap<Instruction *, unsigned>::iterator MTPI;
std::tie(MTPI, Inserted) =
MemTransferSliceMap.insert(std::make_pair(&II, AS.Slices.size()));
unsigned PrevIdx = MTPI->second;
if (!Inserted) {
Slice &PrevP = AS.Slices[PrevIdx];
// Check if the begin offsets match and this is a non-volatile transfer.
// In that case, we can completely elide the transfer.
if (!II.isVolatile() && PrevP.beginOffset() == RawOffset) {
PrevP.kill();
return markAsDead(II);
}
// Otherwise we have an offset transfer within the same alloca. We can't
// split those.
PrevP.makeUnsplittable();
}
// Insert the use now that we've fixed up the splittable nature.
insertUse(II, Offset, Size, /*IsSplittable=*/Inserted && Length);
// Check that we ended up with a valid index in the map.
assert(AS.Slices[PrevIdx].getUse()->getUser() == &II &&
"Map index doesn't point back to a slice with this user.");
}
// Disable SRoA for any intrinsics except for lifetime invariants.
// FIXME: What about debug intrinsics? This matches old behavior, but
// doesn't make sense.
void visitIntrinsicInst(IntrinsicInst &II) {
if (!IsOffsetKnown)
return PI.setAborted(&II);
if (II.getIntrinsicID() == Intrinsic::lifetime_start ||
II.getIntrinsicID() == Intrinsic::lifetime_end) {
ConstantInt *Length = cast<ConstantInt>(II.getArgOperand(0));
uint64_t Size = std::min(AllocSize - Offset.getLimitedValue(),
Length->getLimitedValue());
insertUse(II, Offset, Size, true);
return;
}
Base::visitIntrinsicInst(II);
}
Instruction *hasUnsafePHIOrSelectUse(Instruction *Root, uint64_t &Size) {
// We consider any PHI or select that results in a direct load or store of
// the same offset to be a viable use for slicing purposes. These uses
// are considered unsplittable and the size is the maximum loaded or stored
// size.
SmallPtrSet<Instruction *, 4> Visited;
SmallVector<std::pair<Instruction *, Instruction *>, 4> Uses;
Visited.insert(Root);
Uses.push_back(std::make_pair(cast<Instruction>(*U), Root));
const DataLayout &DL = Root->getModule()->getDataLayout();
// If there are no loads or stores, the access is dead. We mark that as
// a size zero access.
Size = 0;
do {
Instruction *I, *UsedI;
std::tie(UsedI, I) = Uses.pop_back_val();
if (LoadInst *LI = dyn_cast<LoadInst>(I)) {
Size = std::max(Size, DL.getTypeStoreSize(LI->getType()));
continue;
}
if (StoreInst *SI = dyn_cast<StoreInst>(I)) {
Value *Op = SI->getOperand(0);
if (Op == UsedI)
return SI;
Size = std::max(Size, DL.getTypeStoreSize(Op->getType()));
continue;
}
if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(I)) {
if (!GEP->hasAllZeroIndices())
return GEP;
} else if (!isa<BitCastInst>(I) && !isa<PHINode>(I) &&
!isa<SelectInst>(I)) {
return I;
}
for (User *U : I->users())
if (Visited.insert(cast<Instruction>(U)).second)
Uses.push_back(std::make_pair(I, cast<Instruction>(U)));
} while (!Uses.empty());
return nullptr;
}
void visitPHINodeOrSelectInst(Instruction &I) {
assert(isa<PHINode>(I) || isa<SelectInst>(I));
if (I.use_empty())
return markAsDead(I);
// TODO: We could use SimplifyInstruction here to fold PHINodes and
// SelectInsts. However, doing so requires to change the current
// dead-operand-tracking mechanism. For instance, suppose neither loading
// from %U nor %other traps. Then "load (select undef, %U, %other)" does not
// trap either. However, if we simply replace %U with undef using the
// current dead-operand-tracking mechanism, "load (select undef, undef,
// %other)" may trap because the select may return the first operand
// "undef".
if (Value *Result = foldPHINodeOrSelectInst(I)) {
if (Result == *U)
// If the result of the constant fold will be the pointer, recurse
// through the PHI/select as if we had RAUW'ed it.
enqueueUsers(I);
else
// Otherwise the operand to the PHI/select is dead, and we can replace
// it with undef.
AS.DeadOperands.push_back(U);
return;
}
if (!IsOffsetKnown)
return PI.setAborted(&I);
// See if we already have computed info on this node.
uint64_t &Size = PHIOrSelectSizes[&I];
if (!Size) {
// This is a new PHI/Select, check for an unsafe use of it.
if (Instruction *UnsafeI = hasUnsafePHIOrSelectUse(&I, Size))
return PI.setAborted(UnsafeI);
}
// For PHI and select operands outside the alloca, we can't nuke the entire
// phi or select -- the other side might still be relevant, so we special
// case them here and use a separate structure to track the operands
// themselves which should be replaced with undef.
// FIXME: This should instead be escaped in the event we're instrumenting
// for address sanitization.
if (Offset.uge(AllocSize)) {
AS.DeadOperands.push_back(U);
return;
}
insertUse(I, Offset, Size);
}
void visitPHINode(PHINode &PN) { visitPHINodeOrSelectInst(PN); }
void visitSelectInst(SelectInst &SI) { visitPHINodeOrSelectInst(SI); }
/// \brief Disable SROA entirely if there are unhandled users of the alloca.
void visitInstruction(Instruction &I) { PI.setAborted(&I); }
};
AllocaSlices::AllocaSlices(const DataLayout &DL, AllocaInst &AI)
:
#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
AI(AI),
#endif
PointerEscapingInstr(nullptr) {
SliceBuilder PB(DL, AI, *this);
SliceBuilder::PtrInfo PtrI = PB.visitPtr(AI);
if (PtrI.isEscaped() || PtrI.isAborted()) {
// FIXME: We should sink the escape vs. abort info into the caller nicely,
// possibly by just storing the PtrInfo in the AllocaSlices.
PointerEscapingInstr = PtrI.getEscapingInst() ? PtrI.getEscapingInst()
: PtrI.getAbortingInst();
assert(PointerEscapingInstr && "Did not track a bad instruction");
return;
}
Slices.erase(std::remove_if(Slices.begin(), Slices.end(),
[](const Slice &S) {
return S.isDead();
}),
Slices.end());
#ifndef NDEBUG
if (SROARandomShuffleSlices) {
std::mt19937 MT(static_cast<unsigned>(sys::TimeValue::now().msec()));
std::shuffle(Slices.begin(), Slices.end(), MT);
}
#endif
// Sort the uses. This arranges for the offsets to be in ascending order,
// and the sizes to be in descending order.
std::sort(Slices.begin(), Slices.end());
}
#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
void AllocaSlices::print(raw_ostream &OS, const_iterator I,
StringRef Indent) const {
printSlice(OS, I, Indent);
OS << "\n";
printUse(OS, I, Indent);
}
void AllocaSlices::printSlice(raw_ostream &OS, const_iterator I,
StringRef Indent) const {
OS << Indent << "[" << I->beginOffset() << "," << I->endOffset() << ")"
<< " slice #" << (I - begin())
<< (I->isSplittable() ? " (splittable)" : "");
}
void AllocaSlices::printUse(raw_ostream &OS, const_iterator I,
StringRef Indent) const {
OS << Indent << " used by: " << *I->getUse()->getUser() << "\n";
}
void AllocaSlices::print(raw_ostream &OS) const {
if (PointerEscapingInstr) {
OS << "Can't analyze slices for alloca: " << AI << "\n"
<< " A pointer to this alloca escaped by:\n"
<< " " << *PointerEscapingInstr << "\n";
return;
}
OS << "Slices of alloca: " << AI << "\n";
for (const_iterator I = begin(), E = end(); I != E; ++I)
print(OS, I);
}
LLVM_DUMP_METHOD void AllocaSlices::dump(const_iterator I) const {
print(dbgs(), I);
}
LLVM_DUMP_METHOD void AllocaSlices::dump() const { print(dbgs()); }
#endif // !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
/// Walk the range of a partitioning looking for a common type to cover this
/// sequence of slices.
static Type *findCommonType(AllocaSlices::const_iterator B,
AllocaSlices::const_iterator E,
uint64_t EndOffset) {
Type *Ty = nullptr;
bool TyIsCommon = true;
IntegerType *ITy = nullptr;
// Note that we need to look at *every* alloca slice's Use to ensure we
// always get consistent results regardless of the order of slices.
for (AllocaSlices::const_iterator I = B; I != E; ++I) {
Use *U = I->getUse();
if (isa<IntrinsicInst>(*U->getUser()))
continue;
if (I->beginOffset() != B->beginOffset() || I->endOffset() != EndOffset)
continue;
Type *UserTy = nullptr;
if (LoadInst *LI = dyn_cast<LoadInst>(U->getUser())) {
UserTy = LI->getType();
} else if (StoreInst *SI = dyn_cast<StoreInst>(U->getUser())) {
UserTy = SI->getValueOperand()->getType();
}
if (IntegerType *UserITy = dyn_cast_or_null<IntegerType>(UserTy)) {
// If the type is larger than the partition, skip it. We only encounter
// this for split integer operations where we want to use the type of the
// entity causing the split. Also skip if the type is not a byte width
// multiple.
if (UserITy->getBitWidth() % 8 != 0 ||
UserITy->getBitWidth() / 8 > (EndOffset - B->beginOffset()))
continue;
// Track the largest bitwidth integer type used in this way in case there
// is no common type.
if (!ITy || ITy->getBitWidth() < UserITy->getBitWidth())
ITy = UserITy;
}
// To avoid depending on the order of slices, Ty and TyIsCommon must not
// depend on types skipped above.
if (!UserTy || (Ty && Ty != UserTy))
TyIsCommon = false; // Give up on anything but an iN type.
else
Ty = UserTy;
}
return TyIsCommon ? Ty : ITy;
}
/// PHI instructions that use an alloca and are subsequently loaded can be
/// rewritten to load both input pointers in the pred blocks and then PHI the
/// results, allowing the load of the alloca to be promoted.
/// From this:
/// %P2 = phi [i32* %Alloca, i32* %Other]
/// %V = load i32* %P2
/// to:
/// %V1 = load i32* %Alloca -> will be mem2reg'd
/// ...
/// %V2 = load i32* %Other
/// ...
/// %V = phi [i32 %V1, i32 %V2]
///
/// We can do this to a select if its only uses are loads and if the operands
/// to the select can be loaded unconditionally.
///
/// FIXME: This should be hoisted into a generic utility, likely in
/// Transforms/Util/Local.h
static bool isSafePHIToSpeculate(PHINode &PN) {
// For now, we can only do this promotion if the load is in the same block
// as the PHI, and if there are no stores between the phi and load.
// TODO: Allow recursive phi users.
// TODO: Allow stores.
BasicBlock *BB = PN.getParent();
unsigned MaxAlign = 0;
bool HaveLoad = false;
for (User *U : PN.users()) {
LoadInst *LI = dyn_cast<LoadInst>(U);
if (!LI || !LI->isSimple())
return false;
// For now we only allow loads in the same block as the PHI. This is
// a common case that happens when instcombine merges two loads through
// a PHI.
if (LI->getParent() != BB)
return false;
// Ensure that there are no instructions between the PHI and the load that
// could store.
for (BasicBlock::iterator BBI(PN); &*BBI != LI; ++BBI)
if (BBI->mayWriteToMemory())
return false;
MaxAlign = std::max(MaxAlign, LI->getAlignment());
HaveLoad = true;
}
if (!HaveLoad)
return false;
const DataLayout &DL = PN.getModule()->getDataLayout();
// We can only transform this if it is safe to push the loads into the
// predecessor blocks. The only thing to watch out for is that we can't put
// a possibly trapping load in the predecessor if it is a critical edge.
for (unsigned Idx = 0, Num = PN.getNumIncomingValues(); Idx != Num; ++Idx) {
TerminatorInst *TI = PN.getIncomingBlock(Idx)->getTerminator();
Value *InVal = PN.getIncomingValue(Idx);
// If the value is produced by the terminator of the predecessor (an
// invoke) or it has side-effects, there is no valid place to put a load
// in the predecessor.
if (TI == InVal || TI->mayHaveSideEffects())
return false;
// If the predecessor has a single successor, then the edge isn't
// critical.
if (TI->getNumSuccessors() == 1)
continue;
// If this pointer is always safe to load, or if we can prove that there
// is already a load in the block, then we can move the load to the pred
// block.
if (isSafeToLoadUnconditionally(InVal, MaxAlign, DL, TI))
continue;
return false;
}
return true;
}
static void speculatePHINodeLoads(PHINode &PN) {
DEBUG(dbgs() << " original: " << PN << "\n");
Type *LoadTy = cast<PointerType>(PN.getType())->getElementType();
IRBuilderTy PHIBuilder(&PN);
PHINode *NewPN = PHIBuilder.CreatePHI(LoadTy, PN.getNumIncomingValues(),
PN.getName() + ".sroa.speculated");
// Get the AA tags and alignment to use from one of the loads. It doesn't
// matter which one we get and if any differ.
LoadInst *SomeLoad = cast<LoadInst>(PN.user_back());
AAMDNodes AATags;
SomeLoad->getAAMetadata(AATags);
unsigned Align = SomeLoad->getAlignment();
// Rewrite all loads of the PN to use the new PHI.
while (!PN.use_empty()) {
LoadInst *LI = cast<LoadInst>(PN.user_back());
LI->replaceAllUsesWith(NewPN);
LI->eraseFromParent();
}
// Inject loads into all of the pred blocks.
for (unsigned Idx = 0, Num = PN.getNumIncomingValues(); Idx != Num; ++Idx) {
BasicBlock *Pred = PN.getIncomingBlock(Idx);
TerminatorInst *TI = Pred->getTerminator();
Value *InVal = PN.getIncomingValue(Idx);
IRBuilderTy PredBuilder(TI);
LoadInst *Load = PredBuilder.CreateLoad(
InVal, (PN.getName() + ".sroa.speculate.load." + Pred->getName()));
++NumLoadsSpeculated;
Load->setAlignment(Align);
if (AATags)
Load->setAAMetadata(AATags);
NewPN->addIncoming(Load, Pred);
}
DEBUG(dbgs() << " speculated to: " << *NewPN << "\n");
PN.eraseFromParent();
}
/// Select instructions that use an alloca and are subsequently loaded can be
/// rewritten to load both input pointers and then select between the result,
/// allowing the load of the alloca to be promoted.
/// From this:
/// %P2 = select i1 %cond, i32* %Alloca, i32* %Other
/// %V = load i32* %P2
/// to:
/// %V1 = load i32* %Alloca -> will be mem2reg'd
/// %V2 = load i32* %Other
/// %V = select i1 %cond, i32 %V1, i32 %V2
///
/// We can do this to a select if its only uses are loads and if the operand
/// to the select can be loaded unconditionally.
static bool isSafeSelectToSpeculate(SelectInst &SI) {
Value *TValue = SI.getTrueValue();
Value *FValue = SI.getFalseValue();
const DataLayout &DL = SI.getModule()->getDataLayout();
for (User *U : SI.users()) {
LoadInst *LI = dyn_cast<LoadInst>(U);
if (!LI || !LI->isSimple())
return false;
// Both operands to the select need to be dereferencable, either
// absolutely (e.g. allocas) or at this point because we can see other
// accesses to it.
if (!isSafeToLoadUnconditionally(TValue, LI->getAlignment(), DL, LI))
return false;
if (!isSafeToLoadUnconditionally(FValue, LI->getAlignment(), DL, LI))
return false;
}
return true;
}
static void speculateSelectInstLoads(SelectInst &SI) {
DEBUG(dbgs() << " original: " << SI << "\n");
IRBuilderTy IRB(&SI);
Value *TV = SI.getTrueValue();
Value *FV = SI.getFalseValue();
// Replace the loads of the select with a select of two loads.
while (!SI.use_empty()) {
LoadInst *LI = cast<LoadInst>(SI.user_back());
assert(LI->isSimple() && "We only speculate simple loads");
IRB.SetInsertPoint(LI);
LoadInst *TL =
IRB.CreateLoad(TV, LI->getName() + ".sroa.speculate.load.true");
LoadInst *FL =
IRB.CreateLoad(FV, LI->getName() + ".sroa.speculate.load.false");
NumLoadsSpeculated += 2;
// Transfer alignment and AA info if present.
TL->setAlignment(LI->getAlignment());
FL->setAlignment(LI->getAlignment());
AAMDNodes Tags;
LI->getAAMetadata(Tags);
if (Tags) {
TL->setAAMetadata(Tags);
FL->setAAMetadata(Tags);
}
Value *V = IRB.CreateSelect(SI.getCondition(), TL, FL,
LI->getName() + ".sroa.speculated");
DEBUG(dbgs() << " speculated to: " << *V << "\n");
LI->replaceAllUsesWith(V);
LI->eraseFromParent();
}
SI.eraseFromParent();
}
/// \brief Build a GEP out of a base pointer and indices.
///
/// This will return the BasePtr if that is valid, or build a new GEP
/// instruction using the IRBuilder if GEP-ing is needed.
static Value *buildGEP(IRBuilderTy &IRB, Value *BasePtr,
SmallVectorImpl<Value *> &Indices, Twine NamePrefix) {
if (Indices.empty())
return BasePtr;
// A single zero index is a no-op, so check for this and avoid building a GEP
// in that case.
if (Indices.size() == 1 && cast<ConstantInt>(Indices.back())->isZero())
return BasePtr;
return IRB.CreateInBoundsGEP(nullptr, BasePtr, Indices,
NamePrefix + "sroa_idx");
}
/// \brief Get a natural GEP off of the BasePtr walking through Ty toward
/// TargetTy without changing the offset of the pointer.
///
/// This routine assumes we've already established a properly offset GEP with
/// Indices, and arrived at the Ty type. The goal is to continue to GEP with
/// zero-indices down through type layers until we find one the same as
/// TargetTy. If we can't find one with the same type, we at least try to use
/// one with the same size. If none of that works, we just produce the GEP as
/// indicated by Indices to have the correct offset.
static Value *getNaturalGEPWithType(IRBuilderTy &IRB, const DataLayout &DL,
Value *BasePtr, Type *Ty, Type *TargetTy,
SmallVectorImpl<Value *> &Indices,
Twine NamePrefix) {
if (Ty == TargetTy)
return buildGEP(IRB, BasePtr, Indices, NamePrefix);
// Pointer size to use for the indices.
unsigned PtrSize = DL.getPointerTypeSizeInBits(BasePtr->getType());
// See if we can descend into a struct and locate a field with the correct
// type.
unsigned NumLayers = 0;
Type *ElementTy = Ty;
do {
if (ElementTy->isPointerTy())
break;
if (ArrayType *ArrayTy = dyn_cast<ArrayType>(ElementTy)) {
ElementTy = ArrayTy->getElementType();
Indices.push_back(IRB.getIntN(PtrSize, 0));
} else if (VectorType *VectorTy = dyn_cast<VectorType>(ElementTy)) {
ElementTy = VectorTy->getElementType();
Indices.push_back(IRB.getInt32(0));
} else if (StructType *STy = dyn_cast<StructType>(ElementTy)) {
if (STy->element_begin() == STy->element_end())
break; // Nothing left to descend into.
ElementTy = *STy->element_begin();
Indices.push_back(IRB.getInt32(0));
} else {
break;
}
++NumLayers;
} while (ElementTy != TargetTy);
if (ElementTy != TargetTy)
Indices.erase(Indices.end() - NumLayers, Indices.end());
return buildGEP(IRB, BasePtr, Indices, NamePrefix);
}
/// \brief Recursively compute indices for a natural GEP.
///
/// This is the recursive step for getNaturalGEPWithOffset that walks down the
/// element types adding appropriate indices for the GEP.
static Value *getNaturalGEPRecursively(IRBuilderTy &IRB, const DataLayout &DL,
Value *Ptr, Type *Ty, APInt &Offset,
Type *TargetTy,
SmallVectorImpl<Value *> &Indices,
Twine NamePrefix) {
if (Offset == 0)
return getNaturalGEPWithType(IRB, DL, Ptr, Ty, TargetTy, Indices,
NamePrefix);
// We can't recurse through pointer types.
if (Ty->isPointerTy())
return nullptr;
// We try to analyze GEPs over vectors here, but note that these GEPs are
// extremely poorly defined currently. The long-term goal is to remove GEPing
// over a vector from the IR completely.
if (VectorType *VecTy = dyn_cast<VectorType>(Ty)) {
unsigned ElementSizeInBits = DL.getTypeSizeInBits(VecTy->getScalarType());
if (ElementSizeInBits % 8 != 0) {
// GEPs over non-multiple of 8 size vector elements are invalid.
return nullptr;
}
APInt ElementSize(Offset.getBitWidth(), ElementSizeInBits / 8);
APInt NumSkippedElements = Offset.sdiv(ElementSize);
if (NumSkippedElements.ugt(VecTy->getNumElements()))
return nullptr;
Offset -= NumSkippedElements * ElementSize;
Indices.push_back(IRB.getInt(NumSkippedElements));
return getNaturalGEPRecursively(IRB, DL, Ptr, VecTy->getElementType(),
Offset, TargetTy, Indices, NamePrefix);
}
if (ArrayType *ArrTy = dyn_cast<ArrayType>(Ty)) {
Type *ElementTy = ArrTy->getElementType();
APInt ElementSize(Offset.getBitWidth(), DL.getTypeAllocSize(ElementTy));
APInt NumSkippedElements = Offset.sdiv(ElementSize);
if (NumSkippedElements.ugt(ArrTy->getNumElements()))
return nullptr;
Offset -= NumSkippedElements * ElementSize;
Indices.push_back(IRB.getInt(NumSkippedElements));
return getNaturalGEPRecursively(IRB, DL, Ptr, ElementTy, Offset, TargetTy,
Indices, NamePrefix);
}
StructType *STy = dyn_cast<StructType>(Ty);
if (!STy)
return nullptr;
const StructLayout *SL = DL.getStructLayout(STy);
uint64_t StructOffset = Offset.getZExtValue();
if (StructOffset >= SL->getSizeInBytes())
return nullptr;
unsigned Index = SL->getElementContainingOffset(StructOffset);
Offset -= APInt(Offset.getBitWidth(), SL->getElementOffset(Index));
Type *ElementTy = STy->getElementType(Index);
if (Offset.uge(DL.getTypeAllocSize(ElementTy)))
return nullptr; // The offset points into alignment padding.
Indices.push_back(IRB.getInt32(Index));
return getNaturalGEPRecursively(IRB, DL, Ptr, ElementTy, Offset, TargetTy,
Indices, NamePrefix);
}
/// \brief Get a natural GEP from a base pointer to a particular offset and
/// resulting in a particular type.
///
/// The goal is to produce a "natural" looking GEP that works with the existing
/// composite types to arrive at the appropriate offset and element type for
/// a pointer. TargetTy is the element type the returned GEP should point-to if
/// possible. We recurse by decreasing Offset, adding the appropriate index to
/// Indices, and setting Ty to the result subtype.
///
/// If no natural GEP can be constructed, this function returns null.
static Value *getNaturalGEPWithOffset(IRBuilderTy &IRB, const DataLayout &DL,
Value *Ptr, APInt Offset, Type *TargetTy,
SmallVectorImpl<Value *> &Indices,
Twine NamePrefix) {
PointerType *Ty = cast<PointerType>(Ptr->getType());
// Don't consider any GEPs through an i8* as natural unless the TargetTy is
// an i8.
if (Ty == IRB.getInt8PtrTy(Ty->getAddressSpace()) && TargetTy->isIntegerTy(8))
return nullptr;
Type *ElementTy = Ty->getElementType();
if (!ElementTy->isSized())
return nullptr; // We can't GEP through an unsized element.
APInt ElementSize(Offset.getBitWidth(), DL.getTypeAllocSize(ElementTy));
if (ElementSize == 0)
return nullptr; // Zero-length arrays can't help us build a natural GEP.
APInt NumSkippedElements = Offset.sdiv(ElementSize);
Offset -= NumSkippedElements * ElementSize;
Indices.push_back(IRB.getInt(NumSkippedElements));
return getNaturalGEPRecursively(IRB, DL, Ptr, ElementTy, Offset, TargetTy,
Indices, NamePrefix);
}
/// \brief Compute an adjusted pointer from Ptr by Offset bytes where the
/// resulting pointer has PointerTy.
///
/// This tries very hard to compute a "natural" GEP which arrives at the offset
/// and produces the pointer type desired. Where it cannot, it will try to use
/// the natural GEP to arrive at the offset and bitcast to the type. Where that
/// fails, it will try to use an existing i8* and GEP to the byte offset and
/// bitcast to the type.
///
/// The strategy for finding the more natural GEPs is to peel off layers of the
/// pointer, walking back through bit casts and GEPs, searching for a base
/// pointer from which we can compute a natural GEP with the desired
/// properties. The algorithm tries to fold as many constant indices into
/// a single GEP as possible, thus making each GEP more independent of the
/// surrounding code.
static Value *getAdjustedPtr(IRBuilderTy &IRB, const DataLayout &DL, Value *Ptr,
APInt Offset, Type *PointerTy, Twine NamePrefix) {
// Even though we don't look through PHI nodes, we could be called on an
// instruction in an unreachable block, which may be on a cycle.
SmallPtrSet<Value *, 4> Visited;
Visited.insert(Ptr);
SmallVector<Value *, 4> Indices;
// We may end up computing an offset pointer that has the wrong type. If we
// never are able to compute one directly that has the correct type, we'll
// fall back to it, so keep it and the base it was computed from around here.
Value *OffsetPtr = nullptr;
Value *OffsetBasePtr;
// Remember any i8 pointer we come across to re-use if we need to do a raw
// byte offset.
Value *Int8Ptr = nullptr;
APInt Int8PtrOffset(Offset.getBitWidth(), 0);
Type *TargetTy = PointerTy->getPointerElementType();
do {
// First fold any existing GEPs into the offset.
while (GEPOperator *GEP = dyn_cast<GEPOperator>(Ptr)) {
APInt GEPOffset(Offset.getBitWidth(), 0);
if (!GEP->accumulateConstantOffset(DL, GEPOffset))
break;
Offset += GEPOffset;
Ptr = GEP->getPointerOperand();
if (!Visited.insert(Ptr).second)
break;
}
// See if we can perform a natural GEP here.
Indices.clear();
if (Value *P = getNaturalGEPWithOffset(IRB, DL, Ptr, Offset, TargetTy,
Indices, NamePrefix)) {
// If we have a new natural pointer at the offset, clear out any old
// offset pointer we computed. Unless it is the base pointer or
// a non-instruction, we built a GEP we don't need. Zap it.
if (OffsetPtr && OffsetPtr != OffsetBasePtr)
if (Instruction *I = dyn_cast<Instruction>(OffsetPtr)) {
assert(I->use_empty() && "Built a GEP with uses some how!");
I->eraseFromParent();
}
OffsetPtr = P;
OffsetBasePtr = Ptr;
// If we also found a pointer of the right type, we're done.
if (P->getType() == PointerTy)
return P;
}
// Stash this pointer if we've found an i8*.
if (Ptr->getType()->isIntegerTy(8)) {
Int8Ptr = Ptr;
Int8PtrOffset = Offset;
}
// Peel off a layer of the pointer and update the offset appropriately.
if (Operator::getOpcode(Ptr) == Instruction::BitCast) {
Ptr = cast<Operator>(Ptr)->getOperand(0);
} else if (GlobalAlias *GA = dyn_cast<GlobalAlias>(Ptr)) {
if (GA->isInterposable())
break;
Ptr = GA->getAliasee();
} else {
break;
}
assert(Ptr->getType()->isPointerTy() && "Unexpected operand type!");
} while (Visited.insert(Ptr).second);
if (!OffsetPtr) {
if (!Int8Ptr) {
Int8Ptr = IRB.CreateBitCast(
Ptr, IRB.getInt8PtrTy(PointerTy->getPointerAddressSpace()),
NamePrefix + "sroa_raw_cast");
Int8PtrOffset = Offset;
}
OffsetPtr = Int8PtrOffset == 0
? Int8Ptr
: IRB.CreateInBoundsGEP(IRB.getInt8Ty(), Int8Ptr,
IRB.getInt(Int8PtrOffset),
NamePrefix + "sroa_raw_idx");
}
Ptr = OffsetPtr;
// On the off chance we were targeting i8*, guard the bitcast here.
if (Ptr->getType() != PointerTy)
Ptr = IRB.CreateBitCast(Ptr, PointerTy, NamePrefix + "sroa_cast");
return Ptr;
}
/// \brief Compute the adjusted alignment for a load or store from an offset.
static unsigned getAdjustedAlignment(Instruction *I, uint64_t Offset,
const DataLayout &DL) {
unsigned Alignment;
Type *Ty;
if (auto *LI = dyn_cast<LoadInst>(I)) {
Alignment = LI->getAlignment();
Ty = LI->getType();
} else if (auto *SI = dyn_cast<StoreInst>(I)) {
Alignment = SI->getAlignment();
Ty = SI->getValueOperand()->getType();
} else {
llvm_unreachable("Only loads and stores are allowed!");
}
if (!Alignment)
Alignment = DL.getABITypeAlignment(Ty);
return MinAlign(Alignment, Offset);
}
/// \brief Test whether we can convert a value from the old to the new type.
///
/// This predicate should be used to guard calls to convertValue in order to
/// ensure that we only try to convert viable values. The strategy is that we
/// will peel off single element struct and array wrappings to get to an
/// underlying value, and convert that value.
static bool canConvertValue(const DataLayout &DL, Type *OldTy, Type *NewTy) {
if (OldTy == NewTy)
return true;
// For integer types, we can't handle any bit-width differences. This would
// break both vector conversions with extension and introduce endianness
// issues when in conjunction with loads and stores.
if (isa<IntegerType>(OldTy) && isa<IntegerType>(NewTy)) {
assert(cast<IntegerType>(OldTy)->getBitWidth() !=
cast<IntegerType>(NewTy)->getBitWidth() &&
"We can't have the same bitwidth for different int types");
return false;
}
if (DL.getTypeSizeInBits(NewTy) != DL.getTypeSizeInBits(OldTy))
return false;
if (!NewTy->isSingleValueType() || !OldTy->isSingleValueType())
return false;
// We can convert pointers to integers and vice-versa. Same for vectors
// of pointers and integers.
OldTy = OldTy->getScalarType();
NewTy = NewTy->getScalarType();
if (NewTy->isPointerTy() || OldTy->isPointerTy()) {
if (NewTy->isPointerTy() && OldTy->isPointerTy()) {
return cast<PointerType>(NewTy)->getPointerAddressSpace() ==
cast<PointerType>(OldTy)->getPointerAddressSpace();
}
if (NewTy->isIntegerTy() || OldTy->isIntegerTy())
return true;
return false;
}
return true;
}
/// \brief Generic routine to convert an SSA value to a value of a different
/// type.
///
/// This will try various different casting techniques, such as bitcasts,
/// inttoptr, and ptrtoint casts. Use the \c canConvertValue predicate to test
/// two types for viability with this routine.
static Value *convertValue(const DataLayout &DL, IRBuilderTy &IRB, Value *V,
Type *NewTy) {
Type *OldTy = V->getType();
assert(canConvertValue(DL, OldTy, NewTy) && "Value not convertable to type");
if (OldTy == NewTy)
return V;
assert(!(isa<IntegerType>(OldTy) && isa<IntegerType>(NewTy)) &&
"Integer types must be the exact same to convert.");
// See if we need inttoptr for this type pair. A cast involving both scalars
// and vectors requires and additional bitcast.
if (OldTy->getScalarType()->isIntegerTy() &&
NewTy->getScalarType()->isPointerTy()) {
// Expand <2 x i32> to i8* --> <2 x i32> to i64 to i8*
if (OldTy->isVectorTy() && !NewTy->isVectorTy())
return IRB.CreateIntToPtr(IRB.CreateBitCast(V, DL.getIntPtrType(NewTy)),
NewTy);
// Expand i128 to <2 x i8*> --> i128 to <2 x i64> to <2 x i8*>
if (!OldTy->isVectorTy() && NewTy->isVectorTy())
return IRB.CreateIntToPtr(IRB.CreateBitCast(V, DL.getIntPtrType(NewTy)),
NewTy);
return IRB.CreateIntToPtr(V, NewTy);
}
// See if we need ptrtoint for this type pair. A cast involving both scalars
// and vectors requires and additional bitcast.
if (OldTy->getScalarType()->isPointerTy() &&
NewTy->getScalarType()->isIntegerTy()) {
// Expand <2 x i8*> to i128 --> <2 x i8*> to <2 x i64> to i128
if (OldTy->isVectorTy() && !NewTy->isVectorTy())
return IRB.CreateBitCast(IRB.CreatePtrToInt(V, DL.getIntPtrType(OldTy)),
NewTy);
// Expand i8* to <2 x i32> --> i8* to i64 to <2 x i32>
if (!OldTy->isVectorTy() && NewTy->isVectorTy())
return IRB.CreateBitCast(IRB.CreatePtrToInt(V, DL.getIntPtrType(OldTy)),
NewTy);
return IRB.CreatePtrToInt(V, NewTy);
}
return IRB.CreateBitCast(V, NewTy);
}
/// \brief Test whether the given slice use can be promoted to a vector.
///
/// This function is called to test each entry in a partition which is slated
/// for a single slice.
static bool isVectorPromotionViableForSlice(Partition &P, const Slice &S,
VectorType *Ty,
uint64_t ElementSize,
const DataLayout &DL) {
// First validate the slice offsets.
uint64_t BeginOffset =
std::max(S.beginOffset(), P.beginOffset()) - P.beginOffset();
uint64_t BeginIndex = BeginOffset / ElementSize;
if (BeginIndex * ElementSize != BeginOffset ||
BeginIndex >= Ty->getNumElements())
return false;
uint64_t EndOffset =
std::min(S.endOffset(), P.endOffset()) - P.beginOffset();
uint64_t EndIndex = EndOffset / ElementSize;
if (EndIndex * ElementSize != EndOffset || EndIndex > Ty->getNumElements())
return false;
assert(EndIndex > BeginIndex && "Empty vector!");
uint64_t NumElements = EndIndex - BeginIndex;
Type *SliceTy = (NumElements == 1)
? Ty->getElementType()
: VectorType::get(Ty->getElementType(), NumElements);
Type *SplitIntTy =
Type::getIntNTy(Ty->getContext(), NumElements * ElementSize * 8);
Use *U = S.getUse();
if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(U->getUser())) {
if (MI->isVolatile())
return false;
if (!S.isSplittable())
return false; // Skip any unsplittable intrinsics.
} else if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(U->getUser())) {
if (II->getIntrinsicID() != Intrinsic::lifetime_start &&
II->getIntrinsicID() != Intrinsic::lifetime_end)
return false;
} else if (U->get()->getType()->getPointerElementType()->isStructTy()) {
// Disable vector promotion when there are loads or stores of an FCA.
return false;
} else if (LoadInst *LI = dyn_cast<LoadInst>(U->getUser())) {
if (LI->isVolatile())
return false;
Type *LTy = LI->getType();
if (P.beginOffset() > S.beginOffset() || P.endOffset() < S.endOffset()) {
assert(LTy->isIntegerTy());
LTy = SplitIntTy;
}
if (!canConvertValue(DL, SliceTy, LTy))
return false;
} else if (StoreInst *SI = dyn_cast<StoreInst>(U->getUser())) {
if (SI->isVolatile())
return false;
Type *STy = SI->getValueOperand()->getType();
if (P.beginOffset() > S.beginOffset() || P.endOffset() < S.endOffset()) {
assert(STy->isIntegerTy());
STy = SplitIntTy;
}
if (!canConvertValue(DL, STy, SliceTy))
return false;
} else {
return false;
}
return true;
}
/// \brief Test whether the given alloca partitioning and range of slices can be
/// promoted to a vector.
///
/// This is a quick test to check whether we can rewrite a particular alloca
/// partition (and its newly formed alloca) into a vector alloca with only
/// whole-vector loads and stores such that it could be promoted to a vector
/// SSA value. We only can ensure this for a limited set of operations, and we
/// don't want to do the rewrites unless we are confident that the result will
/// be promotable, so we have an early test here.
static VectorType *isVectorPromotionViable(Partition &P, const DataLayout &DL) {
// Collect the candidate types for vector-based promotion. Also track whether
// we have different element types.
SmallVector<VectorType *, 4> CandidateTys;
Type *CommonEltTy = nullptr;
bool HaveCommonEltTy = true;
auto CheckCandidateType = [&](Type *Ty) {
if (auto *VTy = dyn_cast<VectorType>(Ty)) {
CandidateTys.push_back(VTy);
if (!CommonEltTy)
CommonEltTy = VTy->getElementType();
else if (CommonEltTy != VTy->getElementType())
HaveCommonEltTy = false;
}
};
// Consider any loads or stores that are the exact size of the slice.
for (const Slice &S : P)
if (S.beginOffset() == P.beginOffset() &&
S.endOffset() == P.endOffset()) {
if (auto *LI = dyn_cast<LoadInst>(S.getUse()->getUser()))
CheckCandidateType(LI->getType());
else if (auto *SI = dyn_cast<StoreInst>(S.getUse()->getUser()))
CheckCandidateType(SI->getValueOperand()->getType());
}
// If we didn't find a vector type, nothing to do here.
if (CandidateTys.empty())
return nullptr;
// Remove non-integer vector types if we had multiple common element types.
// FIXME: It'd be nice to replace them with integer vector types, but we can't
// do that until all the backends are known to produce good code for all
// integer vector types.
if (!HaveCommonEltTy) {
CandidateTys.erase(std::remove_if(CandidateTys.begin(), CandidateTys.end(),
[](VectorType *VTy) {
return !VTy->getElementType()->isIntegerTy();
}),
CandidateTys.end());
// If there were no integer vector types, give up.
if (CandidateTys.empty())
return nullptr;
// Rank the remaining candidate vector types. This is easy because we know
// they're all integer vectors. We sort by ascending number of elements.
auto RankVectorTypes = [&DL](VectorType *RHSTy, VectorType *LHSTy) {
assert(DL.getTypeSizeInBits(RHSTy) == DL.getTypeSizeInBits(LHSTy) &&
"Cannot have vector types of different sizes!");
assert(RHSTy->getElementType()->isIntegerTy() &&
"All non-integer types eliminated!");
assert(LHSTy->getElementType()->isIntegerTy() &&
"All non-integer types eliminated!");
return RHSTy->getNumElements() < LHSTy->getNumElements();
};
std::sort(CandidateTys.begin(), CandidateTys.end(), RankVectorTypes);
CandidateTys.erase(
std::unique(CandidateTys.begin(), CandidateTys.end(), RankVectorTypes),
CandidateTys.end());
} else {
// The only way to have the same element type in every vector type is to
// have the same vector type. Check that and remove all but one.
#ifndef NDEBUG
for (VectorType *VTy : CandidateTys) {
assert(VTy->getElementType() == CommonEltTy &&
"Unaccounted for element type!");
assert(VTy == CandidateTys[0] &&
"Different vector types with the same element type!");
}
#endif
CandidateTys.resize(1);
}
// Try each vector type, and return the one which works.
auto CheckVectorTypeForPromotion = [&](VectorType *VTy) {
uint64_t ElementSize = DL.getTypeSizeInBits(VTy->getElementType());
// While the definition of LLVM vectors is bitpacked, we don't support sizes
// that aren't byte sized.
if (ElementSize % 8)
return false;
assert((DL.getTypeSizeInBits(VTy) % 8) == 0 &&
"vector size not a multiple of element size?");
ElementSize /= 8;
for (const Slice &S : P)
if (!isVectorPromotionViableForSlice(P, S, VTy, ElementSize, DL))
return false;
for (const Slice *S : P.splitSliceTails())
if (!isVectorPromotionViableForSlice(P, *S, VTy, ElementSize, DL))
return false;
return true;
};
for (VectorType *VTy : CandidateTys)
if (CheckVectorTypeForPromotion(VTy))
return VTy;
return nullptr;
}
/// \brief Test whether a slice of an alloca is valid for integer widening.
///
/// This implements the necessary checking for the \c isIntegerWideningViable
/// test below on a single slice of the alloca.
static bool isIntegerWideningViableForSlice(const Slice &S,
uint64_t AllocBeginOffset,
Type *AllocaTy,
const DataLayout &DL,
bool &WholeAllocaOp) {
uint64_t Size = DL.getTypeStoreSize(AllocaTy);
uint64_t RelBegin = S.beginOffset() - AllocBeginOffset;
uint64_t RelEnd = S.endOffset() - AllocBeginOffset;
// We can't reasonably handle cases where the load or store extends past
// the end of the alloca's type and into its padding.
if (RelEnd > Size)
return false;
Use *U = S.getUse();
if (LoadInst *LI = dyn_cast<LoadInst>(U->getUser())) {
if (LI->isVolatile())
return false;
// We can't handle loads that extend past the allocated memory.
if (DL.getTypeStoreSize(LI->getType()) > Size)
return false;
// Note that we don't count vector loads or stores as whole-alloca
// operations which enable integer widening because we would prefer to use
// vector widening instead.
if (!isa<VectorType>(LI->getType()) && RelBegin == 0 && RelEnd == Size)
WholeAllocaOp = true;
if (IntegerType *ITy = dyn_cast<IntegerType>(LI->getType())) {
if (ITy->getBitWidth() < DL.getTypeStoreSizeInBits(ITy))
return false;
} else if (RelBegin != 0 || RelEnd != Size ||
!canConvertValue(DL, AllocaTy, LI->getType())) {
// Non-integer loads need to be convertible from the alloca type so that
// they are promotable.
return false;
}
} else if (StoreInst *SI = dyn_cast<StoreInst>(U->getUser())) {
Type *ValueTy = SI->getValueOperand()->getType();
if (SI->isVolatile())
return false;
// We can't handle stores that extend past the allocated memory.
if (DL.getTypeStoreSize(ValueTy) > Size)
return false;
// Note that we don't count vector loads or stores as whole-alloca
// operations which enable integer widening because we would prefer to use
// vector widening instead.
if (!isa<VectorType>(ValueTy) && RelBegin == 0 && RelEnd == Size)
WholeAllocaOp = true;
if (IntegerType *ITy = dyn_cast<IntegerType>(ValueTy)) {
if (ITy->getBitWidth() < DL.getTypeStoreSizeInBits(ITy))
return false;
} else if (RelBegin != 0 || RelEnd != Size ||
!canConvertValue(DL, ValueTy, AllocaTy)) {
// Non-integer stores need to be convertible to the alloca type so that
// they are promotable.
return false;
}
} else if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(U->getUser())) {
if (MI->isVolatile() || !isa<Constant>(MI->getLength()))
return false;
if (!S.isSplittable())
return false; // Skip any unsplittable intrinsics.
} else if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(U->getUser())) {
if (II->getIntrinsicID() != Intrinsic::lifetime_start &&
II->getIntrinsicID() != Intrinsic::lifetime_end)
return false;
} else {
return false;
}
return true;
}
/// \brief Test whether the given alloca partition's integer operations can be
/// widened to promotable ones.
///
/// This is a quick test to check whether we can rewrite the integer loads and
/// stores to a particular alloca into wider loads and stores and be able to
/// promote the resulting alloca.
static bool isIntegerWideningViable(Partition &P, Type *AllocaTy,
const DataLayout &DL) {
uint64_t SizeInBits = DL.getTypeSizeInBits(AllocaTy);
// Don't create integer types larger than the maximum bitwidth.
if (SizeInBits > IntegerType::MAX_INT_BITS)
return false;
// Don't try to handle allocas with bit-padding.
if (SizeInBits != DL.getTypeStoreSizeInBits(AllocaTy))
return false;
// We need to ensure that an integer type with the appropriate bitwidth can
// be converted to the alloca type, whatever that is. We don't want to force
// the alloca itself to have an integer type if there is a more suitable one.
Type *IntTy = Type::getIntNTy(AllocaTy->getContext(), SizeInBits);
if (!canConvertValue(DL, AllocaTy, IntTy) ||
!canConvertValue(DL, IntTy, AllocaTy))
return false;
// While examining uses, we ensure that the alloca has a covering load or
// store. We don't want to widen the integer operations only to fail to
// promote due to some other unsplittable entry (which we may make splittable
// later). However, if there are only splittable uses, go ahead and assume
// that we cover the alloca.
// FIXME: We shouldn't consider split slices that happen to start in the
// partition here...
bool WholeAllocaOp =
P.begin() != P.end() ? false : DL.isLegalInteger(SizeInBits);
for (const Slice &S : P)
if (!isIntegerWideningViableForSlice(S, P.beginOffset(), AllocaTy, DL,
WholeAllocaOp))
return false;
for (const Slice *S : P.splitSliceTails())
if (!isIntegerWideningViableForSlice(*S, P.beginOffset(), AllocaTy, DL,
WholeAllocaOp))
return false;
return WholeAllocaOp;
}
static Value *extractInteger(const DataLayout &DL, IRBuilderTy &IRB, Value *V,
IntegerType *Ty, uint64_t Offset,
const Twine &Name) {
DEBUG(dbgs() << " start: " << *V << "\n");
IntegerType *IntTy = cast<IntegerType>(V->getType());
assert(DL.getTypeStoreSize(Ty) + Offset <= DL.getTypeStoreSize(IntTy) &&
"Element extends past full value");
uint64_t ShAmt = 8 * Offset;
if (DL.isBigEndian())
ShAmt = 8 * (DL.getTypeStoreSize(IntTy) - DL.getTypeStoreSize(Ty) - Offset);
if (ShAmt) {
V = IRB.CreateLShr(V, ShAmt, Name + ".shift");
DEBUG(dbgs() << " shifted: " << *V << "\n");
}
assert(Ty->getBitWidth() <= IntTy->getBitWidth() &&
"Cannot extract to a larger integer!");
if (Ty != IntTy) {
V = IRB.CreateTrunc(V, Ty, Name + ".trunc");
DEBUG(dbgs() << " trunced: " << *V << "\n");
}
return V;
}
static Value *insertInteger(const DataLayout &DL, IRBuilderTy &IRB, Value *Old,
Value *V, uint64_t Offset, const Twine &Name) {
IntegerType *IntTy = cast<IntegerType>(Old->getType());
IntegerType *Ty = cast<IntegerType>(V->getType());
assert(Ty->getBitWidth() <= IntTy->getBitWidth() &&
"Cannot insert a larger integer!");
DEBUG(dbgs() << " start: " << *V << "\n");
if (Ty != IntTy) {
V = IRB.CreateZExt(V, IntTy, Name + ".ext");
DEBUG(dbgs() << " extended: " << *V << "\n");
}
assert(DL.getTypeStoreSize(Ty) + Offset <= DL.getTypeStoreSize(IntTy) &&
"Element store outside of alloca store");
uint64_t ShAmt = 8 * Offset;
if (DL.isBigEndian())
ShAmt = 8 * (DL.getTypeStoreSize(IntTy) - DL.getTypeStoreSize(Ty) - Offset);
if (ShAmt) {
V = IRB.CreateShl(V, ShAmt, Name + ".shift");
DEBUG(dbgs() << " shifted: " << *V << "\n");
}
if (ShAmt || Ty->getBitWidth() < IntTy->getBitWidth()) {
APInt Mask = ~Ty->getMask().zext(IntTy->getBitWidth()).shl(ShAmt);
Old = IRB.CreateAnd(Old, Mask, Name + ".mask");
DEBUG(dbgs() << " masked: " << *Old << "\n");
V = IRB.CreateOr(Old, V, Name + ".insert");
DEBUG(dbgs() << " inserted: " << *V << "\n");
}
return V;
}
static Value *extractVector(IRBuilderTy &IRB, Value *V, unsigned BeginIndex,
unsigned EndIndex, const Twine &Name) {
VectorType *VecTy = cast<VectorType>(V->getType());
unsigned NumElements = EndIndex - BeginIndex;
assert(NumElements <= VecTy->getNumElements() && "Too many elements!");
if (NumElements == VecTy->getNumElements())
return V;
if (NumElements == 1) {
V = IRB.CreateExtractElement(V, IRB.getInt32(BeginIndex),
Name + ".extract");
DEBUG(dbgs() << " extract: " << *V << "\n");
return V;
}
SmallVector<Constant *, 8> Mask;
Mask.reserve(NumElements);
for (unsigned i = BeginIndex; i != EndIndex; ++i)
Mask.push_back(IRB.getInt32(i));
V = IRB.CreateShuffleVector(V, UndefValue::get(V->getType()),
ConstantVector::get(Mask), Name + ".extract");
DEBUG(dbgs() << " shuffle: " << *V << "\n");
return V;
}
static Value *insertVector(IRBuilderTy &IRB, Value *Old, Value *V,
unsigned BeginIndex, const Twine &Name) {
VectorType *VecTy = cast<VectorType>(Old->getType());
assert(VecTy && "Can only insert a vector into a vector");
VectorType *Ty = dyn_cast<VectorType>(V->getType());
if (!Ty) {
// Single element to insert.
V = IRB.CreateInsertElement(Old, V, IRB.getInt32(BeginIndex),
Name + ".insert");
DEBUG(dbgs() << " insert: " << *V << "\n");
return V;
}
assert(Ty->getNumElements() <= VecTy->getNumElements() &&
"Too many elements!");
if (Ty->getNumElements() == VecTy->getNumElements()) {
assert(V->getType() == VecTy && "Vector type mismatch");
return V;
}
unsigned EndIndex = BeginIndex + Ty->getNumElements();
// When inserting a smaller vector into the larger to store, we first
// use a shuffle vector to widen it with undef elements, and then
// a second shuffle vector to select between the loaded vector and the
// incoming vector.
SmallVector<Constant *, 8> Mask;
Mask.reserve(VecTy->getNumElements());
for (unsigned i = 0; i != VecTy->getNumElements(); ++i)
if (i >= BeginIndex && i < EndIndex)
Mask.push_back(IRB.getInt32(i - BeginIndex));
else
Mask.push_back(UndefValue::get(IRB.getInt32Ty()));
V = IRB.CreateShuffleVector(V, UndefValue::get(V->getType()),
ConstantVector::get(Mask), Name + ".expand");
DEBUG(dbgs() << " shuffle: " << *V << "\n");
Mask.clear();
for (unsigned i = 0; i != VecTy->getNumElements(); ++i)
Mask.push_back(IRB.getInt1(i >= BeginIndex && i < EndIndex));
V = IRB.CreateSelect(ConstantVector::get(Mask), V, Old, Name + "blend");
DEBUG(dbgs() << " blend: " << *V << "\n");
return V;
}
/// \brief Visitor to rewrite instructions using p particular slice of an alloca
/// to use a new alloca.
///
/// Also implements the rewriting to vector-based accesses when the partition
/// passes the isVectorPromotionViable predicate. Most of the rewriting logic
/// lives here.
class llvm::sroa::AllocaSliceRewriter
: public InstVisitor<AllocaSliceRewriter, bool> {
// Befriend the base class so it can delegate to private visit methods.
friend class llvm::InstVisitor<AllocaSliceRewriter, bool>;
typedef llvm::InstVisitor<AllocaSliceRewriter, bool> Base;
const DataLayout &DL;
AllocaSlices &AS;
SROA &Pass;
AllocaInst &OldAI, &NewAI;
const uint64_t NewAllocaBeginOffset, NewAllocaEndOffset;
Type *NewAllocaTy;
// This is a convenience and flag variable that will be null unless the new
// alloca's integer operations should be widened to this integer type due to
// passing isIntegerWideningViable above. If it is non-null, the desired
// integer type will be stored here for easy access during rewriting.
IntegerType *IntTy;
// If we are rewriting an alloca partition which can be written as pure
// vector operations, we stash extra information here. When VecTy is
// non-null, we have some strict guarantees about the rewritten alloca:
// - The new alloca is exactly the size of the vector type here.
// - The accesses all either map to the entire vector or to a single
// element.
// - The set of accessing instructions is only one of those handled above
// in isVectorPromotionViable. Generally these are the same access kinds
// which are promotable via mem2reg.
VectorType *VecTy;
Type *ElementTy;
uint64_t ElementSize;
// The original offset of the slice currently being rewritten relative to
// the original alloca.
uint64_t BeginOffset, EndOffset;
// The new offsets of the slice currently being rewritten relative to the
// original alloca.
uint64_t NewBeginOffset, NewEndOffset;
uint64_t SliceSize;
bool IsSplittable;
bool IsSplit;
Use *OldUse;
Instruction *OldPtr;
// Track post-rewrite users which are PHI nodes and Selects.
SmallPtrSetImpl<PHINode *> &PHIUsers;
SmallPtrSetImpl<SelectInst *> &SelectUsers;
// Utility IR builder, whose name prefix is setup for each visited use, and
// the insertion point is set to point to the user.
IRBuilderTy IRB;
public:
AllocaSliceRewriter(const DataLayout &DL, AllocaSlices &AS, SROA &Pass,
AllocaInst &OldAI, AllocaInst &NewAI,
uint64_t NewAllocaBeginOffset,
uint64_t NewAllocaEndOffset, bool IsIntegerPromotable,
VectorType *PromotableVecTy,
SmallPtrSetImpl<PHINode *> &PHIUsers,
SmallPtrSetImpl<SelectInst *> &SelectUsers)
: DL(DL), AS(AS), Pass(Pass), OldAI(OldAI), NewAI(NewAI),
NewAllocaBeginOffset(NewAllocaBeginOffset),
NewAllocaEndOffset(NewAllocaEndOffset),
NewAllocaTy(NewAI.getAllocatedType()),
IntTy(IsIntegerPromotable
? Type::getIntNTy(
NewAI.getContext(),
DL.getTypeSizeInBits(NewAI.getAllocatedType()))
: nullptr),
VecTy(PromotableVecTy),
ElementTy(VecTy ? VecTy->getElementType() : nullptr),
ElementSize(VecTy ? DL.getTypeSizeInBits(ElementTy) / 8 : 0),
BeginOffset(), EndOffset(), IsSplittable(), IsSplit(), OldUse(),
OldPtr(), PHIUsers(PHIUsers), SelectUsers(SelectUsers),
IRB(NewAI.getContext(), ConstantFolder()) {
if (VecTy) {
assert((DL.getTypeSizeInBits(ElementTy) % 8) == 0 &&
"Only multiple-of-8 sized vector elements are viable");
++NumVectorized;
}
assert((!IntTy && !VecTy) || (IntTy && !VecTy) || (!IntTy && VecTy));
}
bool visit(AllocaSlices::const_iterator I) {
bool CanSROA = true;
BeginOffset = I->beginOffset();
EndOffset = I->endOffset();
IsSplittable = I->isSplittable();
IsSplit =
BeginOffset < NewAllocaBeginOffset || EndOffset > NewAllocaEndOffset;
DEBUG(dbgs() << " rewriting " << (IsSplit ? "split " : ""));
DEBUG(AS.printSlice(dbgs(), I, ""));
DEBUG(dbgs() << "\n");
// Compute the intersecting offset range.
assert(BeginOffset < NewAllocaEndOffset);
assert(EndOffset > NewAllocaBeginOffset);
NewBeginOffset = std::max(BeginOffset, NewAllocaBeginOffset);
NewEndOffset = std::min(EndOffset, NewAllocaEndOffset);
SliceSize = NewEndOffset - NewBeginOffset;
OldUse = I->getUse();
OldPtr = cast<Instruction>(OldUse->get());
Instruction *OldUserI = cast<Instruction>(OldUse->getUser());
IRB.SetInsertPoint(OldUserI);
IRB.SetCurrentDebugLocation(OldUserI->getDebugLoc());
IRB.SetNamePrefix(Twine(NewAI.getName()) + "." + Twine(BeginOffset) + ".");
CanSROA &= visit(cast<Instruction>(OldUse->getUser()));
if (VecTy || IntTy)
assert(CanSROA);
return CanSROA;
}
private:
// Make sure the other visit overloads are visible.
using Base::visit;
// Every instruction which can end up as a user must have a rewrite rule.
bool visitInstruction(Instruction &I) {
DEBUG(dbgs() << " !!!! Cannot rewrite: " << I << "\n");
llvm_unreachable("No rewrite rule for this instruction!");
}
Value *getNewAllocaSlicePtr(IRBuilderTy &IRB, Type *PointerTy) {
// Note that the offset computation can use BeginOffset or NewBeginOffset
// interchangeably for unsplit slices.
assert(IsSplit || BeginOffset == NewBeginOffset);
uint64_t Offset = NewBeginOffset - NewAllocaBeginOffset;
#ifndef NDEBUG
StringRef OldName = OldPtr->getName();
// Skip through the last '.sroa.' component of the name.
size_t LastSROAPrefix = OldName.rfind(".sroa.");
if (LastSROAPrefix != StringRef::npos) {
OldName = OldName.substr(LastSROAPrefix + strlen(".sroa."));
// Look for an SROA slice index.
size_t IndexEnd = OldName.find_first_not_of("0123456789");
if (IndexEnd != StringRef::npos && OldName[IndexEnd] == '.') {
// Strip the index and look for the offset.
OldName = OldName.substr(IndexEnd + 1);
size_t OffsetEnd = OldName.find_first_not_of("0123456789");
if (OffsetEnd != StringRef::npos && OldName[OffsetEnd] == '.')
// Strip the offset.
OldName = OldName.substr(OffsetEnd + 1);
}
}
// Strip any SROA suffixes as well.
OldName = OldName.substr(0, OldName.find(".sroa_"));
#endif
return getAdjustedPtr(IRB, DL, &NewAI,
APInt(DL.getPointerSizeInBits(), Offset), PointerTy,
#ifndef NDEBUG
Twine(OldName) + "."
#else
Twine()
#endif
);
}
/// \brief Compute suitable alignment to access this slice of the *new*
/// alloca.
///
/// You can optionally pass a type to this routine and if that type's ABI
/// alignment is itself suitable, this will return zero.
unsigned getSliceAlign(Type *Ty = nullptr) {
unsigned NewAIAlign = NewAI.getAlignment();
if (!NewAIAlign)
NewAIAlign = DL.getABITypeAlignment(NewAI.getAllocatedType());
unsigned Align =
MinAlign(NewAIAlign, NewBeginOffset - NewAllocaBeginOffset);
return (Ty && Align == DL.getABITypeAlignment(Ty)) ? 0 : Align;
}
unsigned getIndex(uint64_t Offset) {
assert(VecTy && "Can only call getIndex when rewriting a vector");
uint64_t RelOffset = Offset - NewAllocaBeginOffset;
assert(RelOffset / ElementSize < UINT32_MAX && "Index out of bounds");
uint32_t Index = RelOffset / ElementSize;
assert(Index * ElementSize == RelOffset);
return Index;
}
void deleteIfTriviallyDead(Value *V) {
Instruction *I = cast<Instruction>(V);
if (isInstructionTriviallyDead(I))
Pass.DeadInsts.insert(I);
}
Value *rewriteVectorizedLoadInst() {
unsigned BeginIndex = getIndex(NewBeginOffset);
unsigned EndIndex = getIndex(NewEndOffset);
assert(EndIndex > BeginIndex && "Empty vector!");
Value *V = IRB.CreateAlignedLoad(&NewAI, NewAI.getAlignment(), "load");
return extractVector(IRB, V, BeginIndex, EndIndex, "vec");
}
Value *rewriteIntegerLoad(LoadInst &LI) {
assert(IntTy && "We cannot insert an integer to the alloca");
assert(!LI.isVolatile());
Value *V = IRB.CreateAlignedLoad(&NewAI, NewAI.getAlignment(), "load");
V = convertValue(DL, IRB, V, IntTy);
assert(NewBeginOffset >= NewAllocaBeginOffset && "Out of bounds offset");
uint64_t Offset = NewBeginOffset - NewAllocaBeginOffset;
if (Offset > 0 || NewEndOffset < NewAllocaEndOffset) {
IntegerType *ExtractTy = Type::getIntNTy(LI.getContext(), SliceSize * 8);
V = extractInteger(DL, IRB, V, ExtractTy, Offset, "extract");
}
// It is possible that the extracted type is not the load type. This
// happens if there is a load past the end of the alloca, and as
// a consequence the slice is narrower but still a candidate for integer
// lowering. To handle this case, we just zero extend the extracted
// integer.
assert(cast<IntegerType>(LI.getType())->getBitWidth() >= SliceSize * 8 &&
"Can only handle an extract for an overly wide load");
if (cast<IntegerType>(LI.getType())->getBitWidth() > SliceSize * 8)
V = IRB.CreateZExt(V, LI.getType());
return V;
}
bool visitLoadInst(LoadInst &LI) {
DEBUG(dbgs() << " original: " << LI << "\n");
Value *OldOp = LI.getOperand(0);
assert(OldOp == OldPtr);
Type *TargetTy = IsSplit ? Type::getIntNTy(LI.getContext(), SliceSize * 8)
: LI.getType();
const bool IsLoadPastEnd = DL.getTypeStoreSize(TargetTy) > SliceSize;
bool IsPtrAdjusted = false;
Value *V;
if (VecTy) {
V = rewriteVectorizedLoadInst();
} else if (IntTy && LI.getType()->isIntegerTy()) {
V = rewriteIntegerLoad(LI);
} else if (NewBeginOffset == NewAllocaBeginOffset &&
NewEndOffset == NewAllocaEndOffset &&
(canConvertValue(DL, NewAllocaTy, TargetTy) ||
(IsLoadPastEnd && NewAllocaTy->isIntegerTy() &&
TargetTy->isIntegerTy()))) {
LoadInst *NewLI = IRB.CreateAlignedLoad(&NewAI, NewAI.getAlignment(),
LI.isVolatile(), LI.getName());
if (LI.isVolatile())
NewLI->setAtomic(LI.getOrdering(), LI.getSynchScope());
V = NewLI;
// If this is an integer load past the end of the slice (which means the
// bytes outside the slice are undef or this load is dead) just forcibly
// fix the integer size with correct handling of endianness.
if (auto *AITy = dyn_cast<IntegerType>(NewAllocaTy))
if (auto *TITy = dyn_cast<IntegerType>(TargetTy))
if (AITy->getBitWidth() < TITy->getBitWidth()) {
V = IRB.CreateZExt(V, TITy, "load.ext");
if (DL.isBigEndian())
V = IRB.CreateShl(V, TITy->getBitWidth() - AITy->getBitWidth(),
"endian_shift");
}
} else {
Type *LTy = TargetTy->getPointerTo();
LoadInst *NewLI = IRB.CreateAlignedLoad(getNewAllocaSlicePtr(IRB, LTy),
getSliceAlign(TargetTy),
LI.isVolatile(), LI.getName());
if (LI.isVolatile())
NewLI->setAtomic(LI.getOrdering(), LI.getSynchScope());
V = NewLI;
IsPtrAdjusted = true;
}
V = convertValue(DL, IRB, V, TargetTy);
if (IsSplit) {
assert(!LI.isVolatile());
assert(LI.getType()->isIntegerTy() &&
"Only integer type loads and stores are split");
assert(SliceSize < DL.getTypeStoreSize(LI.getType()) &&
"Split load isn't smaller than original load");
assert(LI.getType()->getIntegerBitWidth() ==
DL.getTypeStoreSizeInBits(LI.getType()) &&
"Non-byte-multiple bit width");
// Move the insertion point just past the load so that we can refer to it.
IRB.SetInsertPoint(&*std::next(BasicBlock::iterator(&LI)));
// Create a placeholder value with the same type as LI to use as the
// basis for the new value. This allows us to replace the uses of LI with
// the computed value, and then replace the placeholder with LI, leaving
// LI only used for this computation.
Value *Placeholder =
new LoadInst(UndefValue::get(LI.getType()->getPointerTo()));
V = insertInteger(DL, IRB, Placeholder, V, NewBeginOffset - BeginOffset,
"insert");
LI.replaceAllUsesWith(V);
Placeholder->replaceAllUsesWith(&LI);
delete Placeholder;
} else {
LI.replaceAllUsesWith(V);
}
Pass.DeadInsts.insert(&LI);
deleteIfTriviallyDead(OldOp);
DEBUG(dbgs() << " to: " << *V << "\n");
return !LI.isVolatile() && !IsPtrAdjusted;
}
bool rewriteVectorizedStoreInst(Value *V, StoreInst &SI, Value *OldOp) {
if (V->getType() != VecTy) {
unsigned BeginIndex = getIndex(NewBeginOffset);
unsigned EndIndex = getIndex(NewEndOffset);
assert(EndIndex > BeginIndex && "Empty vector!");
unsigned NumElements = EndIndex - BeginIndex;
assert(NumElements <= VecTy->getNumElements() && "Too many elements!");
Type *SliceTy = (NumElements == 1)
? ElementTy
: VectorType::get(ElementTy, NumElements);
if (V->getType() != SliceTy)
V = convertValue(DL, IRB, V, SliceTy);
// Mix in the existing elements.
Value *Old = IRB.CreateAlignedLoad(&NewAI, NewAI.getAlignment(), "load");
V = insertVector(IRB, Old, V, BeginIndex, "vec");
}
StoreInst *Store = IRB.CreateAlignedStore(V, &NewAI, NewAI.getAlignment());
Pass.DeadInsts.insert(&SI);
(void)Store;
DEBUG(dbgs() << " to: " << *Store << "\n");
return true;
}
bool rewriteIntegerStore(Value *V, StoreInst &SI) {
assert(IntTy && "We cannot extract an integer from the alloca");
assert(!SI.isVolatile());
if (DL.getTypeSizeInBits(V->getType()) != IntTy->getBitWidth()) {
Value *Old =
IRB.CreateAlignedLoad(&NewAI, NewAI.getAlignment(), "oldload");
Old = convertValue(DL, IRB, Old, IntTy);
assert(BeginOffset >= NewAllocaBeginOffset && "Out of bounds offset");
uint64_t Offset = BeginOffset - NewAllocaBeginOffset;
V = insertInteger(DL, IRB, Old, SI.getValueOperand(), Offset, "insert");
}
V = convertValue(DL, IRB, V, NewAllocaTy);
StoreInst *Store = IRB.CreateAlignedStore(V, &NewAI, NewAI.getAlignment());
Pass.DeadInsts.insert(&SI);
(void)Store;
DEBUG(dbgs() << " to: " << *Store << "\n");
return true;
}
bool visitStoreInst(StoreInst &SI) {
DEBUG(dbgs() << " original: " << SI << "\n");
Value *OldOp = SI.getOperand(1);
assert(OldOp == OldPtr);
Value *V = SI.getValueOperand();
// Strip all inbounds GEPs and pointer casts to try to dig out any root
// alloca that should be re-examined after promoting this alloca.
if (V->getType()->isPointerTy())
if (AllocaInst *AI = dyn_cast<AllocaInst>(V->stripInBoundsOffsets()))
Pass.PostPromotionWorklist.insert(AI);
if (SliceSize < DL.getTypeStoreSize(V->getType())) {
assert(!SI.isVolatile());
assert(V->getType()->isIntegerTy() &&
"Only integer type loads and stores are split");
assert(V->getType()->getIntegerBitWidth() ==
DL.getTypeStoreSizeInBits(V->getType()) &&
"Non-byte-multiple bit width");
IntegerType *NarrowTy = Type::getIntNTy(SI.getContext(), SliceSize * 8);
V = extractInteger(DL, IRB, V, NarrowTy, NewBeginOffset - BeginOffset,
"extract");
}
if (VecTy)
return rewriteVectorizedStoreInst(V, SI, OldOp);
if (IntTy && V->getType()->isIntegerTy())
return rewriteIntegerStore(V, SI);
const bool IsStorePastEnd = DL.getTypeStoreSize(V->getType()) > SliceSize;
StoreInst *NewSI;
if (NewBeginOffset == NewAllocaBeginOffset &&
NewEndOffset == NewAllocaEndOffset &&
(canConvertValue(DL, V->getType(), NewAllocaTy) ||
(IsStorePastEnd && NewAllocaTy->isIntegerTy() &&
V->getType()->isIntegerTy()))) {
// If this is an integer store past the end of slice (and thus the bytes
// past that point are irrelevant or this is unreachable), truncate the
// value prior to storing.
if (auto *VITy = dyn_cast<IntegerType>(V->getType()))
if (auto *AITy = dyn_cast<IntegerType>(NewAllocaTy))
if (VITy->getBitWidth() > AITy->getBitWidth()) {
if (DL.isBigEndian())
V = IRB.CreateLShr(V, VITy->getBitWidth() - AITy->getBitWidth(),
"endian_shift");
V = IRB.CreateTrunc(V, AITy, "load.trunc");
}
V = convertValue(DL, IRB, V, NewAllocaTy);
NewSI = IRB.CreateAlignedStore(V, &NewAI, NewAI.getAlignment(),
SI.isVolatile());
} else {
Value *NewPtr = getNewAllocaSlicePtr(IRB, V->getType()->getPointerTo());
NewSI = IRB.CreateAlignedStore(V, NewPtr, getSliceAlign(V->getType()),
SI.isVolatile());
}
if (SI.isVolatile())
NewSI->setAtomic(SI.getOrdering(), SI.getSynchScope());
Pass.DeadInsts.insert(&SI);
deleteIfTriviallyDead(OldOp);
DEBUG(dbgs() << " to: " << *NewSI << "\n");
return NewSI->getPointerOperand() == &NewAI && !SI.isVolatile();
}
/// \brief Compute an integer value from splatting an i8 across the given
/// number of bytes.
///
/// Note that this routine assumes an i8 is a byte. If that isn't true, don't
/// call this routine.
/// FIXME: Heed the advice above.
///
/// \param V The i8 value to splat.
/// \param Size The number of bytes in the output (assuming i8 is one byte)
Value *getIntegerSplat(Value *V, unsigned Size) {
assert(Size > 0 && "Expected a positive number of bytes.");
IntegerType *VTy = cast<IntegerType>(V->getType());
assert(VTy->getBitWidth() == 8 && "Expected an i8 value for the byte");
if (Size == 1)
return V;
Type *SplatIntTy = Type::getIntNTy(VTy->getContext(), Size * 8);
V = IRB.CreateMul(
IRB.CreateZExt(V, SplatIntTy, "zext"),
ConstantExpr::getUDiv(
Constant::getAllOnesValue(SplatIntTy),
ConstantExpr::getZExt(Constant::getAllOnesValue(V->getType()),
SplatIntTy)),
"isplat");
return V;
}
/// \brief Compute a vector splat for a given element value.
Value *getVectorSplat(Value *V, unsigned NumElements) {
V = IRB.CreateVectorSplat(NumElements, V, "vsplat");
DEBUG(dbgs() << " splat: " << *V << "\n");
return V;
}
bool visitMemSetInst(MemSetInst &II) {
DEBUG(dbgs() << " original: " << II << "\n");
assert(II.getRawDest() == OldPtr);
// If the memset has a variable size, it cannot be split, just adjust the
// pointer to the new alloca.
if (!isa<Constant>(II.getLength())) {
assert(!IsSplit);
assert(NewBeginOffset == BeginOffset);
II.setDest(getNewAllocaSlicePtr(IRB, OldPtr->getType()));
Type *CstTy = II.getAlignmentCst()->getType();
II.setAlignment(ConstantInt::get(CstTy, getSliceAlign()));
deleteIfTriviallyDead(OldPtr);
return false;
}
// Record this instruction for deletion.
Pass.DeadInsts.insert(&II);
Type *AllocaTy = NewAI.getAllocatedType();
Type *ScalarTy = AllocaTy->getScalarType();
// If this doesn't map cleanly onto the alloca type, and that type isn't
// a single value type, just emit a memset.
if (!VecTy && !IntTy &&
(BeginOffset > NewAllocaBeginOffset || EndOffset < NewAllocaEndOffset ||
SliceSize != DL.getTypeStoreSize(AllocaTy) ||
!AllocaTy->isSingleValueType() ||
!DL.isLegalInteger(DL.getTypeSizeInBits(ScalarTy)) ||
DL.getTypeSizeInBits(ScalarTy) % 8 != 0)) {
Type *SizeTy = II.getLength()->getType();
Constant *Size = ConstantInt::get(SizeTy, NewEndOffset - NewBeginOffset);
CallInst *New = IRB.CreateMemSet(
getNewAllocaSlicePtr(IRB, OldPtr->getType()), II.getValue(), Size,
getSliceAlign(), II.isVolatile());
(void)New;
DEBUG(dbgs() << " to: " << *New << "\n");
return false;
}
// If we can represent this as a simple value, we have to build the actual
// value to store, which requires expanding the byte present in memset to
// a sensible representation for the alloca type. This is essentially
// splatting the byte to a sufficiently wide integer, splatting it across
// any desired vector width, and bitcasting to the final type.
Value *V;
if (VecTy) {
// If this is a memset of a vectorized alloca, insert it.
assert(ElementTy == ScalarTy);
unsigned BeginIndex = getIndex(NewBeginOffset);
unsigned EndIndex = getIndex(NewEndOffset);
assert(EndIndex > BeginIndex && "Empty vector!");
unsigned NumElements = EndIndex - BeginIndex;
assert(NumElements <= VecTy->getNumElements() && "Too many elements!");
Value *Splat =
getIntegerSplat(II.getValue(), DL.getTypeSizeInBits(ElementTy) / 8);
Splat = convertValue(DL, IRB, Splat, ElementTy);
if (NumElements > 1)
Splat = getVectorSplat(Splat, NumElements);
Value *Old =
IRB.CreateAlignedLoad(&NewAI, NewAI.getAlignment(), "oldload");
V = insertVector(IRB, Old, Splat, BeginIndex, "vec");
} else if (IntTy) {
// If this is a memset on an alloca where we can widen stores, insert the
// set integer.
assert(!II.isVolatile());
uint64_t Size = NewEndOffset - NewBeginOffset;
V = getIntegerSplat(II.getValue(), Size);
if (IntTy && (BeginOffset != NewAllocaBeginOffset ||
EndOffset != NewAllocaBeginOffset)) {
Value *Old =
IRB.CreateAlignedLoad(&NewAI, NewAI.getAlignment(), "oldload");
Old = convertValue(DL, IRB, Old, IntTy);
uint64_t Offset = NewBeginOffset - NewAllocaBeginOffset;
V = insertInteger(DL, IRB, Old, V, Offset, "insert");
} else {
assert(V->getType() == IntTy &&
"Wrong type for an alloca wide integer!");
}
V = convertValue(DL, IRB, V, AllocaTy);
} else {
// Established these invariants above.
assert(NewBeginOffset == NewAllocaBeginOffset);
assert(NewEndOffset == NewAllocaEndOffset);
V = getIntegerSplat(II.getValue(), DL.getTypeSizeInBits(ScalarTy) / 8);
if (VectorType *AllocaVecTy = dyn_cast<VectorType>(AllocaTy))
V = getVectorSplat(V, AllocaVecTy->getNumElements());
V = convertValue(DL, IRB, V, AllocaTy);
}
Value *New = IRB.CreateAlignedStore(V, &NewAI, NewAI.getAlignment(),
II.isVolatile());
(void)New;
DEBUG(dbgs() << " to: " << *New << "\n");
return !II.isVolatile();
}
bool visitMemTransferInst(MemTransferInst &II) {
// Rewriting of memory transfer instructions can be a bit tricky. We break
// them into two categories: split intrinsics and unsplit intrinsics.
DEBUG(dbgs() << " original: " << II << "\n");
bool IsDest = &II.getRawDestUse() == OldUse;
assert((IsDest && II.getRawDest() == OldPtr) ||
(!IsDest && II.getRawSource() == OldPtr));
unsigned SliceAlign = getSliceAlign();
// For unsplit intrinsics, we simply modify the source and destination
// pointers in place. This isn't just an optimization, it is a matter of
// correctness. With unsplit intrinsics we may be dealing with transfers
// within a single alloca before SROA ran, or with transfers that have
// a variable length. We may also be dealing with memmove instead of
// memcpy, and so simply updating the pointers is the necessary for us to
// update both source and dest of a single call.
if (!IsSplittable) {
Value *AdjustedPtr = getNewAllocaSlicePtr(IRB, OldPtr->getType());
if (IsDest)
II.setDest(AdjustedPtr);
else
II.setSource(AdjustedPtr);
if (II.getAlignment() > SliceAlign) {
Type *CstTy = II.getAlignmentCst()->getType();
II.setAlignment(
ConstantInt::get(CstTy, MinAlign(II.getAlignment(), SliceAlign)));
}
DEBUG(dbgs() << " to: " << II << "\n");
deleteIfTriviallyDead(OldPtr);
return false;
}
// For split transfer intrinsics we have an incredibly useful assurance:
// the source and destination do not reside within the same alloca, and at
// least one of them does not escape. This means that we can replace
// memmove with memcpy, and we don't need to worry about all manner of
// downsides to splitting and transforming the operations.
// If this doesn't map cleanly onto the alloca type, and that type isn't
// a single value type, just emit a memcpy.
bool EmitMemCpy =
!VecTy && !IntTy &&
(BeginOffset > NewAllocaBeginOffset || EndOffset < NewAllocaEndOffset ||
SliceSize != DL.getTypeStoreSize(NewAI.getAllocatedType()) ||
!NewAI.getAllocatedType()->isSingleValueType());
// If we're just going to emit a memcpy, the alloca hasn't changed, and the
// size hasn't been shrunk based on analysis of the viable range, this is
// a no-op.
if (EmitMemCpy && &OldAI == &NewAI) {
// Ensure the start lines up.
assert(NewBeginOffset == BeginOffset);
// Rewrite the size as needed.
if (NewEndOffset != EndOffset)
II.setLength(ConstantInt::get(II.getLength()->getType(),
NewEndOffset - NewBeginOffset));
return false;
}
// Record this instruction for deletion.
Pass.DeadInsts.insert(&II);
// Strip all inbounds GEPs and pointer casts to try to dig out any root
// alloca that should be re-examined after rewriting this instruction.
Value *OtherPtr = IsDest ? II.getRawSource() : II.getRawDest();
if (AllocaInst *AI =
dyn_cast<AllocaInst>(OtherPtr->stripInBoundsOffsets())) {
assert(AI != &OldAI && AI != &NewAI &&
"Splittable transfers cannot reach the same alloca on both ends.");
Pass.Worklist.insert(AI);
}
Type *OtherPtrTy = OtherPtr->getType();
unsigned OtherAS = OtherPtrTy->getPointerAddressSpace();
// Compute the relative offset for the other pointer within the transfer.
unsigned IntPtrWidth = DL.getPointerSizeInBits(OtherAS);
APInt OtherOffset(IntPtrWidth, NewBeginOffset - BeginOffset);
unsigned OtherAlign = MinAlign(II.getAlignment() ? II.getAlignment() : 1,
OtherOffset.zextOrTrunc(64).getZExtValue());
if (EmitMemCpy) {
// Compute the other pointer, folding as much as possible to produce
// a single, simple GEP in most cases.
OtherPtr = getAdjustedPtr(IRB, DL, OtherPtr, OtherOffset, OtherPtrTy,
OtherPtr->getName() + ".");
Value *OurPtr = getNewAllocaSlicePtr(IRB, OldPtr->getType());
Type *SizeTy = II.getLength()->getType();
Constant *Size = ConstantInt::get(SizeTy, NewEndOffset - NewBeginOffset);
CallInst *New = IRB.CreateMemCpy(
IsDest ? OurPtr : OtherPtr, IsDest ? OtherPtr : OurPtr, Size,
MinAlign(SliceAlign, OtherAlign), II.isVolatile());
(void)New;
DEBUG(dbgs() << " to: " << *New << "\n");
return false;
}
bool IsWholeAlloca = NewBeginOffset == NewAllocaBeginOffset &&
NewEndOffset == NewAllocaEndOffset;
uint64_t Size = NewEndOffset - NewBeginOffset;
unsigned BeginIndex = VecTy ? getIndex(NewBeginOffset) : 0;
unsigned EndIndex = VecTy ? getIndex(NewEndOffset) : 0;
unsigned NumElements = EndIndex - BeginIndex;
IntegerType *SubIntTy =
IntTy ? Type::getIntNTy(IntTy->getContext(), Size * 8) : nullptr;
// Reset the other pointer type to match the register type we're going to
// use, but using the address space of the original other pointer.
if (VecTy && !IsWholeAlloca) {
if (NumElements == 1)
OtherPtrTy = VecTy->getElementType();
else
OtherPtrTy = VectorType::get(VecTy->getElementType(), NumElements);
OtherPtrTy = OtherPtrTy->getPointerTo(OtherAS);
} else if (IntTy && !IsWholeAlloca) {
OtherPtrTy = SubIntTy->getPointerTo(OtherAS);
} else {
OtherPtrTy = NewAllocaTy->getPointerTo(OtherAS);
}
Value *SrcPtr = getAdjustedPtr(IRB, DL, OtherPtr, OtherOffset, OtherPtrTy,
OtherPtr->getName() + ".");
unsigned SrcAlign = OtherAlign;
Value *DstPtr = &NewAI;
unsigned DstAlign = SliceAlign;
if (!IsDest) {
std::swap(SrcPtr, DstPtr);
std::swap(SrcAlign, DstAlign);
}
Value *Src;
if (VecTy && !IsWholeAlloca && !IsDest) {
Src = IRB.CreateAlignedLoad(&NewAI, NewAI.getAlignment(), "load");
Src = extractVector(IRB, Src, BeginIndex, EndIndex, "vec");
} else if (IntTy && !IsWholeAlloca && !IsDest) {
Src = IRB.CreateAlignedLoad(&NewAI, NewAI.getAlignment(), "load");
Src = convertValue(DL, IRB, Src, IntTy);
uint64_t Offset = NewBeginOffset - NewAllocaBeginOffset;
Src = extractInteger(DL, IRB, Src, SubIntTy, Offset, "extract");
} else {
Src =
IRB.CreateAlignedLoad(SrcPtr, SrcAlign, II.isVolatile(), "copyload");
}
if (VecTy && !IsWholeAlloca && IsDest) {
Value *Old =
IRB.CreateAlignedLoad(&NewAI, NewAI.getAlignment(), "oldload");
Src = insertVector(IRB, Old, Src, BeginIndex, "vec");
} else if (IntTy && !IsWholeAlloca && IsDest) {
Value *Old =
IRB.CreateAlignedLoad(&NewAI, NewAI.getAlignment(), "oldload");
Old = convertValue(DL, IRB, Old, IntTy);
uint64_t Offset = NewBeginOffset - NewAllocaBeginOffset;
Src = insertInteger(DL, IRB, Old, Src, Offset, "insert");
Src = convertValue(DL, IRB, Src, NewAllocaTy);
}
StoreInst *Store = cast<StoreInst>(
IRB.CreateAlignedStore(Src, DstPtr, DstAlign, II.isVolatile()));
(void)Store;
DEBUG(dbgs() << " to: " << *Store << "\n");
return !II.isVolatile();
}
bool visitIntrinsicInst(IntrinsicInst &II) {
assert(II.getIntrinsicID() == Intrinsic::lifetime_start ||
II.getIntrinsicID() == Intrinsic::lifetime_end);
DEBUG(dbgs() << " original: " << II << "\n");
assert(II.getArgOperand(1) == OldPtr);
// Record this instruction for deletion.
Pass.DeadInsts.insert(&II);
ConstantInt *Size =
ConstantInt::get(cast<IntegerType>(II.getArgOperand(0)->getType()),
NewEndOffset - NewBeginOffset);
Value *Ptr = getNewAllocaSlicePtr(IRB, OldPtr->getType());
Value *New;
if (II.getIntrinsicID() == Intrinsic::lifetime_start)
New = IRB.CreateLifetimeStart(Ptr, Size);
else
New = IRB.CreateLifetimeEnd(Ptr, Size);
(void)New;
DEBUG(dbgs() << " to: " << *New << "\n");
return true;
}
bool visitPHINode(PHINode &PN) {
DEBUG(dbgs() << " original: " << PN << "\n");
assert(BeginOffset >= NewAllocaBeginOffset && "PHIs are unsplittable");
assert(EndOffset <= NewAllocaEndOffset && "PHIs are unsplittable");
// We would like to compute a new pointer in only one place, but have it be
// as local as possible to the PHI. To do that, we re-use the location of
// the old pointer, which necessarily must be in the right position to
// dominate the PHI.
IRBuilderTy PtrBuilder(IRB);
if (isa<PHINode>(OldPtr))
PtrBuilder.SetInsertPoint(&*OldPtr->getParent()->getFirstInsertionPt());
else
PtrBuilder.SetInsertPoint(OldPtr);
PtrBuilder.SetCurrentDebugLocation(OldPtr->getDebugLoc());
Value *NewPtr = getNewAllocaSlicePtr(PtrBuilder, OldPtr->getType());
// Replace the operands which were using the old pointer.
std::replace(PN.op_begin(), PN.op_end(), cast<Value>(OldPtr), NewPtr);
DEBUG(dbgs() << " to: " << PN << "\n");
deleteIfTriviallyDead(OldPtr);
// PHIs can't be promoted on their own, but often can be speculated. We
// check the speculation outside of the rewriter so that we see the
// fully-rewritten alloca.
PHIUsers.insert(&PN);
return true;
}
bool visitSelectInst(SelectInst &SI) {
DEBUG(dbgs() << " original: " << SI << "\n");
assert((SI.getTrueValue() == OldPtr || SI.getFalseValue() == OldPtr) &&
"Pointer isn't an operand!");
assert(BeginOffset >= NewAllocaBeginOffset && "Selects are unsplittable");
assert(EndOffset <= NewAllocaEndOffset && "Selects are unsplittable");
Value *NewPtr = getNewAllocaSlicePtr(IRB, OldPtr->getType());
// Replace the operands which were using the old pointer.
if (SI.getOperand(1) == OldPtr)
SI.setOperand(1, NewPtr);
if (SI.getOperand(2) == OldPtr)
SI.setOperand(2, NewPtr);
DEBUG(dbgs() << " to: " << SI << "\n");
deleteIfTriviallyDead(OldPtr);
// Selects can't be promoted on their own, but often can be speculated. We
// check the speculation outside of the rewriter so that we see the
// fully-rewritten alloca.
SelectUsers.insert(&SI);
return true;
}
};
namespace {
/// \brief Visitor to rewrite aggregate loads and stores as scalar.
///
/// This pass aggressively rewrites all aggregate loads and stores on
/// a particular pointer (or any pointer derived from it which we can identify)
/// with scalar loads and stores.
class AggLoadStoreRewriter : public InstVisitor<AggLoadStoreRewriter, bool> {
// Befriend the base class so it can delegate to private visit methods.
friend class llvm::InstVisitor<AggLoadStoreRewriter, bool>;
/// Queue of pointer uses to analyze and potentially rewrite.
SmallVector<Use *, 8> Queue;
/// Set to prevent us from cycling with phi nodes and loops.
SmallPtrSet<User *, 8> Visited;
/// The current pointer use being rewritten. This is used to dig up the used
/// value (as opposed to the user).
Use *U;
public:
/// Rewrite loads and stores through a pointer and all pointers derived from
/// it.
bool rewrite(Instruction &I) {
DEBUG(dbgs() << " Rewriting FCA loads and stores...\n");
enqueueUsers(I);
bool Changed = false;
while (!Queue.empty()) {
U = Queue.pop_back_val();
Changed |= visit(cast<Instruction>(U->getUser()));
}
return Changed;
}
private:
/// Enqueue all the users of the given instruction for further processing.
/// This uses a set to de-duplicate users.
void enqueueUsers(Instruction &I) {
for (Use &U : I.uses())
if (Visited.insert(U.getUser()).second)
Queue.push_back(&U);
}
// Conservative default is to not rewrite anything.
bool visitInstruction(Instruction &I) { return false; }
/// \brief Generic recursive split emission class.
template <typename Derived> class OpSplitter {
protected:
/// The builder used to form new instructions.
IRBuilderTy IRB;
/// The indices which to be used with insert- or extractvalue to select the
/// appropriate value within the aggregate.
SmallVector<unsigned, 4> Indices;
/// The indices to a GEP instruction which will move Ptr to the correct slot
/// within the aggregate.
SmallVector<Value *, 4> GEPIndices;
/// The base pointer of the original op, used as a base for GEPing the
/// split operations.
Value *Ptr;
/// Initialize the splitter with an insertion point, Ptr and start with a
/// single zero GEP index.
OpSplitter(Instruction *InsertionPoint, Value *Ptr)
: IRB(InsertionPoint), GEPIndices(1, IRB.getInt32(0)), Ptr(Ptr) {}
public:
/// \brief Generic recursive split emission routine.
///
/// This method recursively splits an aggregate op (load or store) into
/// scalar or vector ops. It splits recursively until it hits a single value
/// and emits that single value operation via the template argument.
///
/// The logic of this routine relies on GEPs and insertvalue and
/// extractvalue all operating with the same fundamental index list, merely
/// formatted differently (GEPs need actual values).
///
/// \param Ty The type being split recursively into smaller ops.
/// \param Agg The aggregate value being built up or stored, depending on
/// whether this is splitting a load or a store respectively.
void emitSplitOps(Type *Ty, Value *&Agg, const Twine &Name) {
if (Ty->isSingleValueType())
return static_cast<Derived *>(this)->emitFunc(Ty, Agg, Name);
if (ArrayType *ATy = dyn_cast<ArrayType>(Ty)) {
unsigned OldSize = Indices.size();
(void)OldSize;
for (unsigned Idx = 0, Size = ATy->getNumElements(); Idx != Size;
++Idx) {
assert(Indices.size() == OldSize && "Did not return to the old size");
Indices.push_back(Idx);
GEPIndices.push_back(IRB.getInt32(Idx));
emitSplitOps(ATy->getElementType(), Agg, Name + "." + Twine(Idx));
GEPIndices.pop_back();
Indices.pop_back();
}
return;
}
if (StructType *STy = dyn_cast<StructType>(Ty)) {
unsigned OldSize = Indices.size();
(void)OldSize;
for (unsigned Idx = 0, Size = STy->getNumElements(); Idx != Size;
++Idx) {
assert(Indices.size() == OldSize && "Did not return to the old size");
Indices.push_back(Idx);
GEPIndices.push_back(IRB.getInt32(Idx));
emitSplitOps(STy->getElementType(Idx), Agg, Name + "." + Twine(Idx));
GEPIndices.pop_back();
Indices.pop_back();
}
return;
}
llvm_unreachable("Only arrays and structs are aggregate loadable types");
}
};
struct LoadOpSplitter : public OpSplitter<LoadOpSplitter> {
LoadOpSplitter(Instruction *InsertionPoint, Value *Ptr)
: OpSplitter<LoadOpSplitter>(InsertionPoint, Ptr) {}
/// Emit a leaf load of a single value. This is called at the leaves of the
/// recursive emission to actually load values.
void emitFunc(Type *Ty, Value *&Agg, const Twine &Name) {
assert(Ty->isSingleValueType());
// Load the single value and insert it using the indices.
Value *GEP =
IRB.CreateInBoundsGEP(nullptr, Ptr, GEPIndices, Name + ".gep");
Value *Load = IRB.CreateLoad(GEP, Name + ".load");
Agg = IRB.CreateInsertValue(Agg, Load, Indices, Name + ".insert");
DEBUG(dbgs() << " to: " << *Load << "\n");
}
};
bool visitLoadInst(LoadInst &LI) {
assert(LI.getPointerOperand() == *U);
if (!LI.isSimple() || LI.getType()->isSingleValueType())
return false;
// We have an aggregate being loaded, split it apart.
DEBUG(dbgs() << " original: " << LI << "\n");
LoadOpSplitter Splitter(&LI, *U);
Value *V = UndefValue::get(LI.getType());
Splitter.emitSplitOps(LI.getType(), V, LI.getName() + ".fca");
LI.replaceAllUsesWith(V);
LI.eraseFromParent();
return true;
}
struct StoreOpSplitter : public OpSplitter<StoreOpSplitter> {
StoreOpSplitter(Instruction *InsertionPoint, Value *Ptr)
: OpSplitter<StoreOpSplitter>(InsertionPoint, Ptr) {}
/// Emit a leaf store of a single value. This is called at the leaves of the
/// recursive emission to actually produce stores.
void emitFunc(Type *Ty, Value *&Agg, const Twine &Name) {
assert(Ty->isSingleValueType());
// Extract the single value and store it using the indices.
//
// The gep and extractvalue values are factored out of the CreateStore
// call to make the output independent of the argument evaluation order.
Value *ExtractValue =
IRB.CreateExtractValue(Agg, Indices, Name + ".extract");
Value *InBoundsGEP =
IRB.CreateInBoundsGEP(nullptr, Ptr, GEPIndices, Name + ".gep");
Value *Store = IRB.CreateStore(ExtractValue, InBoundsGEP);
(void)Store;
DEBUG(dbgs() << " to: " << *Store << "\n");
}
};
bool visitStoreInst(StoreInst &SI) {
if (!SI.isSimple() || SI.getPointerOperand() != *U)
return false;
Value *V = SI.getValueOperand();
if (V->getType()->isSingleValueType())
return false;
// We have an aggregate being stored, split it apart.
DEBUG(dbgs() << " original: " << SI << "\n");
StoreOpSplitter Splitter(&SI, *U);
Splitter.emitSplitOps(V->getType(), V, V->getName() + ".fca");
SI.eraseFromParent();
return true;
}
bool visitBitCastInst(BitCastInst &BC) {
enqueueUsers(BC);
return false;
}
bool visitGetElementPtrInst(GetElementPtrInst &GEPI) {
enqueueUsers(GEPI);
return false;
}
bool visitPHINode(PHINode &PN) {
enqueueUsers(PN);
return false;
}
bool visitSelectInst(SelectInst &SI) {
enqueueUsers(SI);
return false;
}
};
}
/// \brief Strip aggregate type wrapping.
///
/// This removes no-op aggregate types wrapping an underlying type. It will
/// strip as many layers of types as it can without changing either the type
/// size or the allocated size.
static Type *stripAggregateTypeWrapping(const DataLayout &DL, Type *Ty) {
if (Ty->isSingleValueType())
return Ty;
uint64_t AllocSize = DL.getTypeAllocSize(Ty);
uint64_t TypeSize = DL.getTypeSizeInBits(Ty);
Type *InnerTy;
if (ArrayType *ArrTy = dyn_cast<ArrayType>(Ty)) {
InnerTy = ArrTy->getElementType();
} else if (StructType *STy = dyn_cast<StructType>(Ty)) {
const StructLayout *SL = DL.getStructLayout(STy);
unsigned Index = SL->getElementContainingOffset(0);
InnerTy = STy->getElementType(Index);
} else {
return Ty;
}
if (AllocSize > DL.getTypeAllocSize(InnerTy) ||
TypeSize > DL.getTypeSizeInBits(InnerTy))
return Ty;
return stripAggregateTypeWrapping(DL, InnerTy);
}
/// \brief Try to find a partition of the aggregate type passed in for a given
/// offset and size.
///
/// This recurses through the aggregate type and tries to compute a subtype
/// based on the offset and size. When the offset and size span a sub-section
/// of an array, it will even compute a new array type for that sub-section,
/// and the same for structs.
///
/// Note that this routine is very strict and tries to find a partition of the
/// type which produces the *exact* right offset and size. It is not forgiving
/// when the size or offset cause either end of type-based partition to be off.
/// Also, this is a best-effort routine. It is reasonable to give up and not
/// return a type if necessary.
static Type *getTypePartition(const DataLayout &DL, Type *Ty, uint64_t Offset,
uint64_t Size) {
if (Offset == 0 && DL.getTypeAllocSize(Ty) == Size)
return stripAggregateTypeWrapping(DL, Ty);
if (Offset > DL.getTypeAllocSize(Ty) ||
(DL.getTypeAllocSize(Ty) - Offset) < Size)
return nullptr;
if (SequentialType *SeqTy = dyn_cast<SequentialType>(Ty)) {
// We can't partition pointers...
if (SeqTy->isPointerTy())
return nullptr;
Type *ElementTy = SeqTy->getElementType();
uint64_t ElementSize = DL.getTypeAllocSize(ElementTy);
uint64_t NumSkippedElements = Offset / ElementSize;
if (ArrayType *ArrTy = dyn_cast<ArrayType>(SeqTy)) {
if (NumSkippedElements >= ArrTy->getNumElements())
return nullptr;
} else if (VectorType *VecTy = dyn_cast<VectorType>(SeqTy)) {
if (NumSkippedElements >= VecTy->getNumElements())
return nullptr;
}
Offset -= NumSkippedElements * ElementSize;
// First check if we need to recurse.
if (Offset > 0 || Size < ElementSize) {
// Bail if the partition ends in a different array element.
if ((Offset + Size) > ElementSize)
return nullptr;
// Recurse through the element type trying to peel off offset bytes.
return getTypePartition(DL, ElementTy, Offset, Size);
}
assert(Offset == 0);
if (Size == ElementSize)
return stripAggregateTypeWrapping(DL, ElementTy);
assert(Size > ElementSize);
uint64_t NumElements = Size / ElementSize;
if (NumElements * ElementSize != Size)
return nullptr;
return ArrayType::get(ElementTy, NumElements);
}
StructType *STy = dyn_cast<StructType>(Ty);
if (!STy)
return nullptr;
const StructLayout *SL = DL.getStructLayout(STy);
if (Offset >= SL->getSizeInBytes())
return nullptr;
uint64_t EndOffset = Offset + Size;
if (EndOffset > SL->getSizeInBytes())
return nullptr;
unsigned Index = SL->getElementContainingOffset(Offset);
Offset -= SL->getElementOffset(Index);
Type *ElementTy = STy->getElementType(Index);
uint64_t ElementSize = DL.getTypeAllocSize(ElementTy);
if (Offset >= ElementSize)
return nullptr; // The offset points into alignment padding.
// See if any partition must be contained by the element.
if (Offset > 0 || Size < ElementSize) {
if ((Offset + Size) > ElementSize)
return nullptr;
return getTypePartition(DL, ElementTy, Offset, Size);
}
assert(Offset == 0);
if (Size == ElementSize)
return stripAggregateTypeWrapping(DL, ElementTy);
StructType::element_iterator EI = STy->element_begin() + Index,
EE = STy->element_end();
if (EndOffset < SL->getSizeInBytes()) {
unsigned EndIndex = SL->getElementContainingOffset(EndOffset);
if (Index == EndIndex)
return nullptr; // Within a single element and its padding.
// Don't try to form "natural" types if the elements don't line up with the
// expected size.
// FIXME: We could potentially recurse down through the last element in the
// sub-struct to find a natural end point.
if (SL->getElementOffset(EndIndex) != EndOffset)
return nullptr;
assert(Index < EndIndex);
EE = STy->element_begin() + EndIndex;
}
// Try to build up a sub-structure.
StructType *SubTy =
StructType::get(STy->getContext(), makeArrayRef(EI, EE), STy->isPacked());
const StructLayout *SubSL = DL.getStructLayout(SubTy);
if (Size != SubSL->getSizeInBytes())
return nullptr; // The sub-struct doesn't have quite the size needed.
return SubTy;
}
/// \brief Pre-split loads and stores to simplify rewriting.
///
/// We want to break up the splittable load+store pairs as much as
/// possible. This is important to do as a preprocessing step, as once we
/// start rewriting the accesses to partitions of the alloca we lose the
/// necessary information to correctly split apart paired loads and stores
/// which both point into this alloca. The case to consider is something like
/// the following:
///
/// %a = alloca [12 x i8]
/// %gep1 = getelementptr [12 x i8]* %a, i32 0, i32 0
/// %gep2 = getelementptr [12 x i8]* %a, i32 0, i32 4
/// %gep3 = getelementptr [12 x i8]* %a, i32 0, i32 8
/// %iptr1 = bitcast i8* %gep1 to i64*
/// %iptr2 = bitcast i8* %gep2 to i64*
/// %fptr1 = bitcast i8* %gep1 to float*
/// %fptr2 = bitcast i8* %gep2 to float*
/// %fptr3 = bitcast i8* %gep3 to float*
/// store float 0.0, float* %fptr1
/// store float 1.0, float* %fptr2
/// %v = load i64* %iptr1
/// store i64 %v, i64* %iptr2
/// %f1 = load float* %fptr2
/// %f2 = load float* %fptr3
///
/// Here we want to form 3 partitions of the alloca, each 4 bytes large, and
/// promote everything so we recover the 2 SSA values that should have been
/// there all along.
///
/// \returns true if any changes are made.
bool SROA::presplitLoadsAndStores(AllocaInst &AI, AllocaSlices &AS) {
DEBUG(dbgs() << "Pre-splitting loads and stores\n");
// Track the loads and stores which are candidates for pre-splitting here, in
// the order they first appear during the partition scan. These give stable
// iteration order and a basis for tracking which loads and stores we
// actually split.
SmallVector<LoadInst *, 4> Loads;
SmallVector<StoreInst *, 4> Stores;
// We need to accumulate the splits required of each load or store where we
// can find them via a direct lookup. This is important to cross-check loads
// and stores against each other. We also track the slice so that we can kill
// all the slices that end up split.
struct SplitOffsets {
Slice *S;
std::vector<uint64_t> Splits;
};
SmallDenseMap<Instruction *, SplitOffsets, 8> SplitOffsetsMap;
// Track loads out of this alloca which cannot, for any reason, be pre-split.
// This is important as we also cannot pre-split stores of those loads!
// FIXME: This is all pretty gross. It means that we can be more aggressive
// in pre-splitting when the load feeding the store happens to come from
// a separate alloca. Put another way, the effectiveness of SROA would be
// decreased by a frontend which just concatenated all of its local allocas
// into one big flat alloca. But defeating such patterns is exactly the job
// SROA is tasked with! Sadly, to not have this discrepancy we would have
// change store pre-splitting to actually force pre-splitting of the load
// that feeds it *and all stores*. That makes pre-splitting much harder, but
// maybe it would make it more principled?
SmallPtrSet<LoadInst *, 8> UnsplittableLoads;
DEBUG(dbgs() << " Searching for candidate loads and stores\n");
for (auto &P : AS.partitions()) {
for (Slice &S : P) {
Instruction *I = cast<Instruction>(S.getUse()->getUser());
if (!S.isSplittable() || S.endOffset() <= P.endOffset()) {
// If this is a load we have to track that it can't participate in any
// pre-splitting. If this is a store of a load we have to track that
// that load also can't participate in any pre-splitting.
if (auto *LI = dyn_cast<LoadInst>(I))
UnsplittableLoads.insert(LI);
else if (auto *SI = dyn_cast<StoreInst>(I))
if (auto *LI = dyn_cast<LoadInst>(SI->getValueOperand()))
UnsplittableLoads.insert(LI);
continue;
}
assert(P.endOffset() > S.beginOffset() &&
"Empty or backwards partition!");
// Determine if this is a pre-splittable slice.
if (auto *LI = dyn_cast<LoadInst>(I)) {
assert(!LI->isVolatile() && "Cannot split volatile loads!");
// The load must be used exclusively to store into other pointers for
// us to be able to arbitrarily pre-split it. The stores must also be
// simple to avoid changing semantics.
auto IsLoadSimplyStored = [](LoadInst *LI) {
for (User *LU : LI->users()) {
auto *SI = dyn_cast<StoreInst>(LU);
if (!SI || !SI->isSimple())
return false;
}
return true;
};
if (!IsLoadSimplyStored(LI)) {
UnsplittableLoads.insert(LI);
continue;
}
Loads.push_back(LI);
} else if (auto *SI = dyn_cast<StoreInst>(I)) {
if (S.getUse() != &SI->getOperandUse(SI->getPointerOperandIndex()))
// Skip stores *of* pointers. FIXME: This shouldn't even be possible!
continue;
auto *StoredLoad = dyn_cast<LoadInst>(SI->getValueOperand());
if (!StoredLoad || !StoredLoad->isSimple())
continue;
assert(!SI->isVolatile() && "Cannot split volatile stores!");
Stores.push_back(SI);
} else {
// Other uses cannot be pre-split.
continue;
}
// Record the initial split.
DEBUG(dbgs() << " Candidate: " << *I << "\n");
auto &Offsets = SplitOffsetsMap[I];
assert(Offsets.Splits.empty() &&
"Should not have splits the first time we see an instruction!");
Offsets.S = &S;
Offsets.Splits.push_back(P.endOffset() - S.beginOffset());
}
// Now scan the already split slices, and add a split for any of them which
// we're going to pre-split.
for (Slice *S : P.splitSliceTails()) {
auto SplitOffsetsMapI =
SplitOffsetsMap.find(cast<Instruction>(S->getUse()->getUser()));
if (SplitOffsetsMapI == SplitOffsetsMap.end())
continue;
auto &Offsets = SplitOffsetsMapI->second;
assert(Offsets.S == S && "Found a mismatched slice!");
assert(!Offsets.Splits.empty() &&
"Cannot have an empty set of splits on the second partition!");
assert(Offsets.Splits.back() ==
P.beginOffset() - Offsets.S->beginOffset() &&
"Previous split does not end where this one begins!");
// Record each split. The last partition's end isn't needed as the size
// of the slice dictates that.
if (S->endOffset() > P.endOffset())
Offsets.Splits.push_back(P.endOffset() - Offsets.S->beginOffset());
}
}
// We may have split loads where some of their stores are split stores. For
// such loads and stores, we can only pre-split them if their splits exactly
// match relative to their starting offset. We have to verify this prior to
// any rewriting.
Stores.erase(
std::remove_if(Stores.begin(), Stores.end(),
[&UnsplittableLoads, &SplitOffsetsMap](StoreInst *SI) {
// Lookup the load we are storing in our map of split
// offsets.
auto *LI = cast<LoadInst>(SI->getValueOperand());
// If it was completely unsplittable, then we're done,
// and this store can't be pre-split.
if (UnsplittableLoads.count(LI))
return true;
auto LoadOffsetsI = SplitOffsetsMap.find(LI);
if (LoadOffsetsI == SplitOffsetsMap.end())
return false; // Unrelated loads are definitely safe.
auto &LoadOffsets = LoadOffsetsI->second;
// Now lookup the store's offsets.
auto &StoreOffsets = SplitOffsetsMap[SI];
// If the relative offsets of each split in the load and
// store match exactly, then we can split them and we
// don't need to remove them here.
if (LoadOffsets.Splits == StoreOffsets.Splits)
return false;
DEBUG(dbgs()
<< " Mismatched splits for load and store:\n"
<< " " << *LI << "\n"
<< " " << *SI << "\n");
// We've found a store and load that we need to split
// with mismatched relative splits. Just give up on them
// and remove both instructions from our list of
// candidates.
UnsplittableLoads.insert(LI);
return true;
}),
Stores.end());
// Now we have to go *back* through all the stores, because a later store may
// have caused an earlier store's load to become unsplittable and if it is
// unsplittable for the later store, then we can't rely on it being split in
// the earlier store either.
Stores.erase(std::remove_if(Stores.begin(), Stores.end(),
[&UnsplittableLoads](StoreInst *SI) {
auto *LI =
cast<LoadInst>(SI->getValueOperand());
return UnsplittableLoads.count(LI);
}),
Stores.end());
// Once we've established all the loads that can't be split for some reason,
// filter any that made it into our list out.
Loads.erase(std::remove_if(Loads.begin(), Loads.end(),
[&UnsplittableLoads](LoadInst *LI) {
return UnsplittableLoads.count(LI);
}),
Loads.end());
// If no loads or stores are left, there is no pre-splitting to be done for
// this alloca.
if (Loads.empty() && Stores.empty())
return false;
// From here on, we can't fail and will be building new accesses, so rig up
// an IR builder.
IRBuilderTy IRB(&AI);
// Collect the new slices which we will merge into the alloca slices.
SmallVector<Slice, 4> NewSlices;
// Track any allocas we end up splitting loads and stores for so we iterate
// on them.
SmallPtrSet<AllocaInst *, 4> ResplitPromotableAllocas;
// At this point, we have collected all of the loads and stores we can
// pre-split, and the specific splits needed for them. We actually do the
// splitting in a specific order in order to handle when one of the loads in
// the value operand to one of the stores.
//
// First, we rewrite all of the split loads, and just accumulate each split
// load in a parallel structure. We also build the slices for them and append
// them to the alloca slices.
SmallDenseMap<LoadInst *, std::vector<LoadInst *>, 1> SplitLoadsMap;
std::vector<LoadInst *> SplitLoads;
const DataLayout &DL = AI.getModule()->getDataLayout();
for (LoadInst *LI : Loads) {
SplitLoads.clear();
IntegerType *Ty = cast<IntegerType>(LI->getType());
uint64_t LoadSize = Ty->getBitWidth() / 8;
assert(LoadSize > 0 && "Cannot have a zero-sized integer load!");
auto &Offsets = SplitOffsetsMap[LI];
assert(LoadSize == Offsets.S->endOffset() - Offsets.S->beginOffset() &&
"Slice size should always match load size exactly!");
uint64_t BaseOffset = Offsets.S->beginOffset();
assert(BaseOffset + LoadSize > BaseOffset &&
"Cannot represent alloca access size using 64-bit integers!");
Instruction *BasePtr = cast<Instruction>(LI->getPointerOperand());
IRB.SetInsertPoint(LI);
DEBUG(dbgs() << " Splitting load: " << *LI << "\n");
uint64_t PartOffset = 0, PartSize = Offsets.Splits.front();
int Idx = 0, Size = Offsets.Splits.size();
for (;;) {
auto *PartTy = Type::getIntNTy(Ty->getContext(), PartSize * 8);
auto *PartPtrTy = PartTy->getPointerTo(LI->getPointerAddressSpace());
LoadInst *PLoad = IRB.CreateAlignedLoad(
getAdjustedPtr(IRB, DL, BasePtr,
APInt(DL.getPointerSizeInBits(), PartOffset),
PartPtrTy, BasePtr->getName() + "."),
getAdjustedAlignment(LI, PartOffset, DL), /*IsVolatile*/ false,
LI->getName());
// Append this load onto the list of split loads so we can find it later
// to rewrite the stores.
SplitLoads.push_back(PLoad);
// Now build a new slice for the alloca.
NewSlices.push_back(
Slice(BaseOffset + PartOffset, BaseOffset + PartOffset + PartSize,
&PLoad->getOperandUse(PLoad->getPointerOperandIndex()),
/*IsSplittable*/ false));
DEBUG(dbgs() << " new slice [" << NewSlices.back().beginOffset()
<< ", " << NewSlices.back().endOffset() << "): " << *PLoad
<< "\n");
// See if we've handled all the splits.
if (Idx >= Size)
break;
// Setup the next partition.
PartOffset = Offsets.Splits[Idx];
++Idx;
PartSize = (Idx < Size ? Offsets.Splits[Idx] : LoadSize) - PartOffset;
}
// Now that we have the split loads, do the slow walk over all uses of the
// load and rewrite them as split stores, or save the split loads to use
// below if the store is going to be split there anyways.
bool DeferredStores = false;
for (User *LU : LI->users()) {
StoreInst *SI = cast<StoreInst>(LU);
if (!Stores.empty() && SplitOffsetsMap.count(SI)) {
DeferredStores = true;
DEBUG(dbgs() << " Deferred splitting of store: " << *SI << "\n");
continue;
}
Value *StoreBasePtr = SI->getPointerOperand();
IRB.SetInsertPoint(SI);
DEBUG(dbgs() << " Splitting store of load: " << *SI << "\n");
for (int Idx = 0, Size = SplitLoads.size(); Idx < Size; ++Idx) {
LoadInst *PLoad = SplitLoads[Idx];
uint64_t PartOffset = Idx == 0 ? 0 : Offsets.Splits[Idx - 1];
auto *PartPtrTy =
PLoad->getType()->getPointerTo(SI->getPointerAddressSpace());
StoreInst *PStore = IRB.CreateAlignedStore(
PLoad, getAdjustedPtr(IRB, DL, StoreBasePtr,
APInt(DL.getPointerSizeInBits(), PartOffset),
PartPtrTy, StoreBasePtr->getName() + "."),
getAdjustedAlignment(SI, PartOffset, DL), /*IsVolatile*/ false);
(void)PStore;
DEBUG(dbgs() << " +" << PartOffset << ":" << *PStore << "\n");
}
// We want to immediately iterate on any allocas impacted by splitting
// this store, and we have to track any promotable alloca (indicated by
// a direct store) as needing to be resplit because it is no longer
// promotable.
if (AllocaInst *OtherAI = dyn_cast<AllocaInst>(StoreBasePtr)) {
ResplitPromotableAllocas.insert(OtherAI);
Worklist.insert(OtherAI);
} else if (AllocaInst *OtherAI = dyn_cast<AllocaInst>(
StoreBasePtr->stripInBoundsOffsets())) {
Worklist.insert(OtherAI);
}
// Mark the original store as dead.
DeadInsts.insert(SI);
}
// Save the split loads if there are deferred stores among the users.
if (DeferredStores)
SplitLoadsMap.insert(std::make_pair(LI, std::move(SplitLoads)));
// Mark the original load as dead and kill the original slice.
DeadInsts.insert(LI);
Offsets.S->kill();
}
// Second, we rewrite all of the split stores. At this point, we know that
// all loads from this alloca have been split already. For stores of such
// loads, we can simply look up the pre-existing split loads. For stores of
// other loads, we split those loads first and then write split stores of
// them.
for (StoreInst *SI : Stores) {
auto *LI = cast<LoadInst>(SI->getValueOperand());
IntegerType *Ty = cast<IntegerType>(LI->getType());
uint64_t StoreSize = Ty->getBitWidth() / 8;
assert(StoreSize > 0 && "Cannot have a zero-sized integer store!");
auto &Offsets = SplitOffsetsMap[SI];
assert(StoreSize == Offsets.S->endOffset() - Offsets.S->beginOffset() &&
"Slice size should always match load size exactly!");
uint64_t BaseOffset = Offsets.S->beginOffset();
assert(BaseOffset + StoreSize > BaseOffset &&
"Cannot represent alloca access size using 64-bit integers!");
Value *LoadBasePtr = LI->getPointerOperand();
Instruction *StoreBasePtr = cast<Instruction>(SI->getPointerOperand());
DEBUG(dbgs() << " Splitting store: " << *SI << "\n");
// Check whether we have an already split load.
auto SplitLoadsMapI = SplitLoadsMap.find(LI);
std::vector<LoadInst *> *SplitLoads = nullptr;
if (SplitLoadsMapI != SplitLoadsMap.end()) {
SplitLoads = &SplitLoadsMapI->second;
assert(SplitLoads->size() == Offsets.Splits.size() + 1 &&
"Too few split loads for the number of splits in the store!");
} else {
DEBUG(dbgs() << " of load: " << *LI << "\n");
}
uint64_t PartOffset = 0, PartSize = Offsets.Splits.front();
int Idx = 0, Size = Offsets.Splits.size();
for (;;) {
auto *PartTy = Type::getIntNTy(Ty->getContext(), PartSize * 8);
auto *PartPtrTy = PartTy->getPointerTo(SI->getPointerAddressSpace());
// Either lookup a split load or create one.
LoadInst *PLoad;
if (SplitLoads) {
PLoad = (*SplitLoads)[Idx];
} else {
IRB.SetInsertPoint(LI);
PLoad = IRB.CreateAlignedLoad(
getAdjustedPtr(IRB, DL, LoadBasePtr,
APInt(DL.getPointerSizeInBits(), PartOffset),
PartPtrTy, LoadBasePtr->getName() + "."),
getAdjustedAlignment(LI, PartOffset, DL), /*IsVolatile*/ false,
LI->getName());
}
// And store this partition.
IRB.SetInsertPoint(SI);
StoreInst *PStore = IRB.CreateAlignedStore(
PLoad, getAdjustedPtr(IRB, DL, StoreBasePtr,
APInt(DL.getPointerSizeInBits(), PartOffset),
PartPtrTy, StoreBasePtr->getName() + "."),
getAdjustedAlignment(SI, PartOffset, DL), /*IsVolatile*/ false);
// Now build a new slice for the alloca.
NewSlices.push_back(
Slice(BaseOffset + PartOffset, BaseOffset + PartOffset + PartSize,
&PStore->getOperandUse(PStore->getPointerOperandIndex()),
/*IsSplittable*/ false));
DEBUG(dbgs() << " new slice [" << NewSlices.back().beginOffset()
<< ", " << NewSlices.back().endOffset() << "): " << *PStore
<< "\n");
if (!SplitLoads) {
DEBUG(dbgs() << " of split load: " << *PLoad << "\n");
}
// See if we've finished all the splits.
if (Idx >= Size)
break;
// Setup the next partition.
PartOffset = Offsets.Splits[Idx];
++Idx;
PartSize = (Idx < Size ? Offsets.Splits[Idx] : StoreSize) - PartOffset;
}
// We want to immediately iterate on any allocas impacted by splitting
// this load, which is only relevant if it isn't a load of this alloca and
// thus we didn't already split the loads above. We also have to keep track
// of any promotable allocas we split loads on as they can no longer be
// promoted.
if (!SplitLoads) {
if (AllocaInst *OtherAI = dyn_cast<AllocaInst>(LoadBasePtr)) {
assert(OtherAI != &AI && "We can't re-split our own alloca!");
ResplitPromotableAllocas.insert(OtherAI);
Worklist.insert(OtherAI);
} else if (AllocaInst *OtherAI = dyn_cast<AllocaInst>(
LoadBasePtr->stripInBoundsOffsets())) {
assert(OtherAI != &AI && "We can't re-split our own alloca!");
Worklist.insert(OtherAI);
}
}
// Mark the original store as dead now that we've split it up and kill its
// slice. Note that we leave the original load in place unless this store
// was its only use. It may in turn be split up if it is an alloca load
// for some other alloca, but it may be a normal load. This may introduce
// redundant loads, but where those can be merged the rest of the optimizer
// should handle the merging, and this uncovers SSA splits which is more
// important. In practice, the original loads will almost always be fully
// split and removed eventually, and the splits will be merged by any
// trivial CSE, including instcombine.
if (LI->hasOneUse()) {
assert(*LI->user_begin() == SI && "Single use isn't this store!");
DeadInsts.insert(LI);
}
DeadInsts.insert(SI);
Offsets.S->kill();
}
// Remove the killed slices that have ben pre-split.
AS.erase(std::remove_if(AS.begin(), AS.end(), [](const Slice &S) {
return S.isDead();
}), AS.end());
// Insert our new slices. This will sort and merge them into the sorted
// sequence.
AS.insert(NewSlices);
DEBUG(dbgs() << " Pre-split slices:\n");
#ifndef NDEBUG
for (auto I = AS.begin(), E = AS.end(); I != E; ++I)
DEBUG(AS.print(dbgs(), I, " "));
#endif
// Finally, don't try to promote any allocas that new require re-splitting.
// They have already been added to the worklist above.
PromotableAllocas.erase(
std::remove_if(
PromotableAllocas.begin(), PromotableAllocas.end(),
[&](AllocaInst *AI) { return ResplitPromotableAllocas.count(AI); }),
PromotableAllocas.end());
return true;
}
/// \brief Rewrite an alloca partition's users.
///
/// This routine drives both of the rewriting goals of the SROA pass. It tries
/// to rewrite uses of an alloca partition to be conducive for SSA value
/// promotion. If the partition needs a new, more refined alloca, this will
/// build that new alloca, preserving as much type information as possible, and
/// rewrite the uses of the old alloca to point at the new one and have the
/// appropriate new offsets. It also evaluates how successful the rewrite was
/// at enabling promotion and if it was successful queues the alloca to be
/// promoted.
AllocaInst *SROA::rewritePartition(AllocaInst &AI, AllocaSlices &AS,
Partition &P) {
// Try to compute a friendly type for this partition of the alloca. This
// won't always succeed, in which case we fall back to a legal integer type
// or an i8 array of an appropriate size.
Type *SliceTy = nullptr;
const DataLayout &DL = AI.getModule()->getDataLayout();
if (Type *CommonUseTy = findCommonType(P.begin(), P.end(), P.endOffset()))
if (DL.getTypeAllocSize(CommonUseTy) >= P.size())
SliceTy = CommonUseTy;
if (!SliceTy)
if (Type *TypePartitionTy = getTypePartition(DL, AI.getAllocatedType(),
P.beginOffset(), P.size()))
SliceTy = TypePartitionTy;
if ((!SliceTy || (SliceTy->isArrayTy() &&
SliceTy->getArrayElementType()->isIntegerTy())) &&
DL.isLegalInteger(P.size() * 8))
SliceTy = Type::getIntNTy(*C, P.size() * 8);
if (!SliceTy)
SliceTy = ArrayType::get(Type::getInt8Ty(*C), P.size());
assert(DL.getTypeAllocSize(SliceTy) >= P.size());
bool IsIntegerPromotable = isIntegerWideningViable(P, SliceTy, DL);
VectorType *VecTy =
IsIntegerPromotable ? nullptr : isVectorPromotionViable(P, DL);
if (VecTy)
SliceTy = VecTy;
// Check for the case where we're going to rewrite to a new alloca of the
// exact same type as the original, and with the same access offsets. In that
// case, re-use the existing alloca, but still run through the rewriter to
// perform phi and select speculation.
AllocaInst *NewAI;
if (SliceTy == AI.getAllocatedType()) {
assert(P.beginOffset() == 0 &&
"Non-zero begin offset but same alloca type");
NewAI = &AI;
// FIXME: We should be able to bail at this point with "nothing changed".
// FIXME: We might want to defer PHI speculation until after here.
// FIXME: return nullptr;
} else {
unsigned Alignment = AI.getAlignment();
if (!Alignment) {
// The minimum alignment which users can rely on when the explicit
// alignment is omitted or zero is that required by the ABI for this
// type.
Alignment = DL.getABITypeAlignment(AI.getAllocatedType());
}
Alignment = MinAlign(Alignment, P.beginOffset());
// If we will get at least this much alignment from the type alone, leave
// the alloca's alignment unconstrained.
if (Alignment <= DL.getABITypeAlignment(SliceTy))
Alignment = 0;
NewAI = new AllocaInst(
SliceTy, nullptr, Alignment,
AI.getName() + ".sroa." + Twine(P.begin() - AS.begin()), &AI);
++NumNewAllocas;
}
DEBUG(dbgs() << "Rewriting alloca partition "
<< "[" << P.beginOffset() << "," << P.endOffset()
<< ") to: " << *NewAI << "\n");
// Track the high watermark on the worklist as it is only relevant for
// promoted allocas. We will reset it to this point if the alloca is not in
// fact scheduled for promotion.
unsigned PPWOldSize = PostPromotionWorklist.size();
unsigned NumUses = 0;
SmallPtrSet<PHINode *, 8> PHIUsers;
SmallPtrSet<SelectInst *, 8> SelectUsers;
AllocaSliceRewriter Rewriter(DL, AS, *this, AI, *NewAI, P.beginOffset(),
P.endOffset(), IsIntegerPromotable, VecTy,
PHIUsers, SelectUsers);
bool Promotable = true;
for (Slice *S : P.splitSliceTails()) {
Promotable &= Rewriter.visit(S);
++NumUses;
}
for (Slice &S : P) {
Promotable &= Rewriter.visit(&S);
++NumUses;
}
NumAllocaPartitionUses += NumUses;
MaxUsesPerAllocaPartition =
std::max<unsigned>(NumUses, MaxUsesPerAllocaPartition);
// Now that we've processed all the slices in the new partition, check if any
// PHIs or Selects would block promotion.
for (SmallPtrSetImpl<PHINode *>::iterator I = PHIUsers.begin(),
E = PHIUsers.end();
I != E; ++I)
if (!isSafePHIToSpeculate(**I)) {
Promotable = false;
PHIUsers.clear();
SelectUsers.clear();
break;
}
for (SmallPtrSetImpl<SelectInst *>::iterator I = SelectUsers.begin(),
E = SelectUsers.end();
I != E; ++I)
if (!isSafeSelectToSpeculate(**I)) {
Promotable = false;
PHIUsers.clear();
SelectUsers.clear();
break;
}
if (Promotable) {
if (PHIUsers.empty() && SelectUsers.empty()) {
// Promote the alloca.
PromotableAllocas.push_back(NewAI);
} else {
// If we have either PHIs or Selects to speculate, add them to those
// worklists and re-queue the new alloca so that we promote in on the
// next iteration.
for (PHINode *PHIUser : PHIUsers)
SpeculatablePHIs.insert(PHIUser);
for (SelectInst *SelectUser : SelectUsers)
SpeculatableSelects.insert(SelectUser);
Worklist.insert(NewAI);
}
} else {
// Drop any post-promotion work items if promotion didn't happen.
while (PostPromotionWorklist.size() > PPWOldSize)
PostPromotionWorklist.pop_back();
// We couldn't promote and we didn't create a new partition, nothing
// happened.
if (NewAI == &AI)
return nullptr;
// If we can't promote the alloca, iterate on it to check for new
// refinements exposed by splitting the current alloca. Don't iterate on an
// alloca which didn't actually change and didn't get promoted.
Worklist.insert(NewAI);
}
return NewAI;
}
/// \brief Walks the slices of an alloca and form partitions based on them,
/// rewriting each of their uses.
bool SROA::splitAlloca(AllocaInst &AI, AllocaSlices &AS) {
if (AS.begin() == AS.end())
return false;
unsigned NumPartitions = 0;
bool Changed = false;
const DataLayout &DL = AI.getModule()->getDataLayout();
// First try to pre-split loads and stores.
Changed |= presplitLoadsAndStores(AI, AS);
// Now that we have identified any pre-splitting opportunities, mark any
// splittable (non-whole-alloca) loads and stores as unsplittable. If we fail
// to split these during pre-splitting, we want to force them to be
// rewritten into a partition.
bool IsSorted = true;
for (Slice &S : AS) {
if (!S.isSplittable())
continue;
// FIXME: We currently leave whole-alloca splittable loads and stores. This
// used to be the only splittable loads and stores and we need to be
// confident that the above handling of splittable loads and stores is
// completely sufficient before we forcibly disable the remaining handling.
if (S.beginOffset() == 0 &&
S.endOffset() >= DL.getTypeAllocSize(AI.getAllocatedType()))
continue;
if (isa<LoadInst>(S.getUse()->getUser()) ||
isa<StoreInst>(S.getUse()->getUser())) {
S.makeUnsplittable();
IsSorted = false;
}
}
if (!IsSorted)
std::sort(AS.begin(), AS.end());
/// \brief Describes the allocas introduced by rewritePartition
/// in order to migrate the debug info.
struct Piece {
AllocaInst *Alloca;
uint64_t Offset;
uint64_t Size;
Piece(AllocaInst *AI, uint64_t O, uint64_t S)
: Alloca(AI), Offset(O), Size(S) {}
};
SmallVector<Piece, 4> Pieces;
// Rewrite each partition.
for (auto &P : AS.partitions()) {
if (AllocaInst *NewAI = rewritePartition(AI, AS, P)) {
Changed = true;
if (NewAI != &AI) {
uint64_t SizeOfByte = 8;
uint64_t AllocaSize = DL.getTypeSizeInBits(NewAI->getAllocatedType());
// Don't include any padding.
uint64_t Size = std::min(AllocaSize, P.size() * SizeOfByte);
Pieces.push_back(Piece(NewAI, P.beginOffset() * SizeOfByte, Size));
}
}
++NumPartitions;
}
NumAllocaPartitions += NumPartitions;
MaxPartitionsPerAlloca =
std::max<unsigned>(NumPartitions, MaxPartitionsPerAlloca);
// Migrate debug information from the old alloca to the new alloca(s)
// and the individual partitions.
if (DbgDeclareInst *DbgDecl = FindAllocaDbgDeclare(&AI)) {
auto *Var = DbgDecl->getVariable();
auto *Expr = DbgDecl->getExpression();
DIBuilder DIB(*AI.getModule(), /*AllowUnresolved*/ false);
uint64_t AllocaSize = DL.getTypeSizeInBits(AI.getAllocatedType());
for (auto Piece : Pieces) {
// Create a piece expression describing the new partition or reuse AI's
// expression if there is only one partition.
auto *PieceExpr = Expr;
if (Piece.Size < AllocaSize || Expr->isBitPiece()) {
// If this alloca is already a scalar replacement of a larger aggregate,
// Piece.Offset describes the offset inside the scalar.
uint64_t Offset = Expr->isBitPiece() ? Expr->getBitPieceOffset() : 0;
uint64_t Start = Offset + Piece.Offset;
uint64_t Size = Piece.Size;
if (Expr->isBitPiece()) {
uint64_t AbsEnd = Expr->getBitPieceOffset() + Expr->getBitPieceSize();
if (Start >= AbsEnd)
// No need to describe a SROAed padding.
continue;
Size = std::min(Size, AbsEnd - Start);
}
PieceExpr = DIB.createBitPieceExpression(Start, Size);
} else {
assert(Pieces.size() == 1 &&
"partition is as large as original alloca");
}
// Remove any existing dbg.declare intrinsic describing the same alloca.
if (DbgDeclareInst *OldDDI = FindAllocaDbgDeclare(Piece.Alloca))
OldDDI->eraseFromParent();
DIB.insertDeclare(Piece.Alloca, Var, PieceExpr, DbgDecl->getDebugLoc(),
&AI);
}
}
return Changed;
}
/// \brief Clobber a use with undef, deleting the used value if it becomes dead.
void SROA::clobberUse(Use &U) {
Value *OldV = U;
// Replace the use with an undef value.
U = UndefValue::get(OldV->getType());
// Check for this making an instruction dead. We have to garbage collect
// all the dead instructions to ensure the uses of any alloca end up being
// minimal.
if (Instruction *OldI = dyn_cast<Instruction>(OldV))
if (isInstructionTriviallyDead(OldI)) {
DeadInsts.insert(OldI);
}
}
/// \brief Analyze an alloca for SROA.
///
/// This analyzes the alloca to ensure we can reason about it, builds
/// the slices of the alloca, and then hands it off to be split and
/// rewritten as needed.
bool SROA::runOnAlloca(AllocaInst &AI) {
DEBUG(dbgs() << "SROA alloca: " << AI << "\n");
++NumAllocasAnalyzed;
// Special case dead allocas, as they're trivial.
if (AI.use_empty()) {
AI.eraseFromParent();
return true;
}
const DataLayout &DL = AI.getModule()->getDataLayout();
// Skip alloca forms that this analysis can't handle.
if (AI.isArrayAllocation() || !AI.getAllocatedType()->isSized() ||
DL.getTypeAllocSize(AI.getAllocatedType()) == 0)
return false;
bool Changed = false;
// First, split any FCA loads and stores touching this alloca to promote
// better splitting and promotion opportunities.
AggLoadStoreRewriter AggRewriter;
Changed |= AggRewriter.rewrite(AI);
// Build the slices using a recursive instruction-visiting builder.
AllocaSlices AS(DL, AI);
DEBUG(AS.print(dbgs()));
if (AS.isEscaped())
return Changed;
// Delete all the dead users of this alloca before splitting and rewriting it.
for (Instruction *DeadUser : AS.getDeadUsers()) {
// Free up everything used by this instruction.
for (Use &DeadOp : DeadUser->operands())
clobberUse(DeadOp);
// Now replace the uses of this instruction.
DeadUser->replaceAllUsesWith(UndefValue::get(DeadUser->getType()));
// And mark it for deletion.
DeadInsts.insert(DeadUser);
Changed = true;
}
for (Use *DeadOp : AS.getDeadOperands()) {
clobberUse(*DeadOp);
Changed = true;
}
// No slices to split. Leave the dead alloca for a later pass to clean up.
if (AS.begin() == AS.end())
return Changed;
Changed |= splitAlloca(AI, AS);
DEBUG(dbgs() << " Speculating PHIs\n");
while (!SpeculatablePHIs.empty())
speculatePHINodeLoads(*SpeculatablePHIs.pop_back_val());
DEBUG(dbgs() << " Speculating Selects\n");
while (!SpeculatableSelects.empty())
speculateSelectInstLoads(*SpeculatableSelects.pop_back_val());
return Changed;
}
/// \brief Delete the dead instructions accumulated in this run.
///
/// Recursively deletes the dead instructions we've accumulated. This is done
/// at the very end to maximize locality of the recursive delete and to
/// minimize the problems of invalidated instruction pointers as such pointers
/// are used heavily in the intermediate stages of the algorithm.
///
/// We also record the alloca instructions deleted here so that they aren't
/// subsequently handed to mem2reg to promote.
void SROA::deleteDeadInstructions(
SmallPtrSetImpl<AllocaInst *> &DeletedAllocas) {
while (!DeadInsts.empty()) {
Instruction *I = DeadInsts.pop_back_val();
DEBUG(dbgs() << "Deleting dead instruction: " << *I << "\n");
I->replaceAllUsesWith(UndefValue::get(I->getType()));
for (Use &Operand : I->operands())
if (Instruction *U = dyn_cast<Instruction>(Operand)) {
// Zero out the operand and see if it becomes trivially dead.
Operand = nullptr;
if (isInstructionTriviallyDead(U))
DeadInsts.insert(U);
}
if (AllocaInst *AI = dyn_cast<AllocaInst>(I)) {
DeletedAllocas.insert(AI);
if (DbgDeclareInst *DbgDecl = FindAllocaDbgDeclare(AI))
DbgDecl->eraseFromParent();
}
++NumDeleted;
I->eraseFromParent();
}
}
/// \brief Promote the allocas, using the best available technique.
///
/// This attempts to promote whatever allocas have been identified as viable in
/// the PromotableAllocas list. If that list is empty, there is nothing to do.
/// This function returns whether any promotion occurred.
bool SROA::promoteAllocas(Function &F) {
if (PromotableAllocas.empty())
return false;
NumPromoted += PromotableAllocas.size();
DEBUG(dbgs() << "Promoting allocas with mem2reg...\n");
PromoteMemToReg(PromotableAllocas, *DT, nullptr, AC);
PromotableAllocas.clear();
return true;
}
PreservedAnalyses SROA::runImpl(Function &F, DominatorTree &RunDT,
AssumptionCache &RunAC) {
DEBUG(dbgs() << "SROA function: " << F.getName() << "\n");
C = &F.getContext();
DT = &RunDT;
AC = &RunAC;
BasicBlock &EntryBB = F.getEntryBlock();
for (BasicBlock::iterator I = EntryBB.begin(), E = std::prev(EntryBB.end());
I != E; ++I) {
if (AllocaInst *AI = dyn_cast<AllocaInst>(I))
Worklist.insert(AI);
}
bool Changed = false;
// A set of deleted alloca instruction pointers which should be removed from
// the list of promotable allocas.
SmallPtrSet<AllocaInst *, 4> DeletedAllocas;
do {
while (!Worklist.empty()) {
Changed |= runOnAlloca(*Worklist.pop_back_val());
deleteDeadInstructions(DeletedAllocas);
// Remove the deleted allocas from various lists so that we don't try to
// continue processing them.
if (!DeletedAllocas.empty()) {
auto IsInSet = [&](AllocaInst *AI) { return DeletedAllocas.count(AI); };
Worklist.remove_if(IsInSet);
PostPromotionWorklist.remove_if(IsInSet);
PromotableAllocas.erase(std::remove_if(PromotableAllocas.begin(),
PromotableAllocas.end(),
IsInSet),
PromotableAllocas.end());
DeletedAllocas.clear();
}
}
Changed |= promoteAllocas(F);
Worklist = PostPromotionWorklist;
PostPromotionWorklist.clear();
} while (!Worklist.empty());
if (!Changed)
return PreservedAnalyses::all();
// FIXME: Even when promoting allocas we should preserve some abstract set of
// CFG-specific analyses.
PreservedAnalyses PA;
PA.preserve<GlobalsAA>();
return PA;
}
PreservedAnalyses SROA::run(Function &F, AnalysisManager<Function> &AM) {
return runImpl(F, AM.getResult<DominatorTreeAnalysis>(F),
AM.getResult<AssumptionAnalysis>(F));
}
/// A legacy pass for the legacy pass manager that wraps the \c SROA pass.
///
/// This is in the llvm namespace purely to allow it to be a friend of the \c
/// SROA pass.
class llvm::sroa::SROALegacyPass : public FunctionPass {
/// The SROA implementation.
SROA Impl;
public:
SROALegacyPass() : FunctionPass(ID) {
initializeSROALegacyPassPass(*PassRegistry::getPassRegistry());
}
bool runOnFunction(Function &F) override {
if (skipFunction(F))
return false;
auto PA = Impl.runImpl(
F, getAnalysis<DominatorTreeWrapperPass>().getDomTree(),
getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F));
return !PA.areAllPreserved();
}
void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.addRequired<AssumptionCacheTracker>();
AU.addRequired<DominatorTreeWrapperPass>();
AU.addPreserved<GlobalsAAWrapperPass>();
AU.setPreservesCFG();
}
const char *getPassName() const override { return "SROA"; }
static char ID;
};
char SROALegacyPass::ID = 0;
FunctionPass *llvm::createSROAPass() { return new SROALegacyPass(); }
INITIALIZE_PASS_BEGIN(SROALegacyPass, "sroa",
"Scalar Replacement Of Aggregates", false, false)
INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
INITIALIZE_PASS_END(SROALegacyPass, "sroa", "Scalar Replacement Of Aggregates",
false, false)