//===- RegisterCoalescer.cpp - Generic Register Coalescing Interface -------==//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements the generic RegisterCoalescer interface which
// is used as the common interface used by all clients and
// implementations of register coalescing.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "regalloc"
#include "RegisterCoalescer.h"
#include "llvm/ADT/OwningPtr.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/SmallSet.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/CodeGen/LiveIntervalAnalysis.h"
#include "llvm/CodeGen/LiveRangeEdit.h"
#include "llvm/CodeGen/MachineFrameInfo.h"
#include "llvm/CodeGen/MachineInstr.h"
#include "llvm/CodeGen/MachineLoopInfo.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/CodeGen/Passes.h"
#include "llvm/CodeGen/RegisterClassInfo.h"
#include "llvm/CodeGen/VirtRegMap.h"
#include "llvm/IR/Value.h"
#include "llvm/Pass.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Target/TargetInstrInfo.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/Target/TargetRegisterInfo.h"
#include "llvm/Target/TargetSubtargetInfo.h"
#include <algorithm>
#include <cmath>
using namespace llvm;
STATISTIC(numJoins , "Number of interval joins performed");
STATISTIC(numCrossRCs , "Number of cross class joins performed");
STATISTIC(numCommutes , "Number of instruction commuting performed");
STATISTIC(numExtends , "Number of copies extended");
STATISTIC(NumReMats , "Number of instructions re-materialized");
STATISTIC(NumInflated , "Number of register classes inflated");
STATISTIC(NumLaneConflicts, "Number of dead lane conflicts tested");
STATISTIC(NumLaneResolves, "Number of dead lane conflicts resolved");
static cl::opt<bool>
EnableJoining("join-liveintervals",
cl::desc("Coalesce copies (default=true)"),
cl::init(true));
// Temporary flag to test critical edge unsplitting.
static cl::opt<bool>
EnableJoinSplits("join-splitedges",
cl::desc("Coalesce copies on split edges (default=subtarget)"), cl::Hidden);
// Temporary flag to test global copy optimization.
static cl::opt<cl::boolOrDefault>
EnableGlobalCopies("join-globalcopies",
cl::desc("Coalesce copies that span blocks (default=subtarget)"),
cl::init(cl::BOU_UNSET), cl::Hidden);
static cl::opt<bool>
VerifyCoalescing("verify-coalescing",
cl::desc("Verify machine instrs before and after register coalescing"),
cl::Hidden);
namespace {
class RegisterCoalescer : public MachineFunctionPass,
private LiveRangeEdit::Delegate {
MachineFunction* MF;
MachineRegisterInfo* MRI;
const TargetMachine* TM;
const TargetRegisterInfo* TRI;
const TargetInstrInfo* TII;
LiveIntervals *LIS;
const MachineLoopInfo* Loops;
AliasAnalysis *AA;
RegisterClassInfo RegClassInfo;
/// \brief True if the coalescer should aggressively coalesce global copies
/// in favor of keeping local copies.
bool JoinGlobalCopies;
/// \brief True if the coalescer should aggressively coalesce fall-thru
/// blocks exclusively containing copies.
bool JoinSplitEdges;
/// WorkList - Copy instructions yet to be coalesced.
SmallVector<MachineInstr*, 8> WorkList;
SmallVector<MachineInstr*, 8> LocalWorkList;
/// ErasedInstrs - Set of instruction pointers that have been erased, and
/// that may be present in WorkList.
SmallPtrSet<MachineInstr*, 8> ErasedInstrs;
/// Dead instructions that are about to be deleted.
SmallVector<MachineInstr*, 8> DeadDefs;
/// Virtual registers to be considered for register class inflation.
SmallVector<unsigned, 8> InflateRegs;
/// Recursively eliminate dead defs in DeadDefs.
void eliminateDeadDefs();
/// LiveRangeEdit callback.
void LRE_WillEraseInstruction(MachineInstr *MI);
/// coalesceLocals - coalesce the LocalWorkList.
void coalesceLocals();
/// joinAllIntervals - join compatible live intervals
void joinAllIntervals();
/// copyCoalesceInMBB - Coalesce copies in the specified MBB, putting
/// copies that cannot yet be coalesced into WorkList.
void copyCoalesceInMBB(MachineBasicBlock *MBB);
/// copyCoalesceWorkList - Try to coalesce all copies in CurrList. Return
/// true if any progress was made.
bool copyCoalesceWorkList(MutableArrayRef<MachineInstr*> CurrList);
/// joinCopy - Attempt to join intervals corresponding to SrcReg/DstReg,
/// which are the src/dst of the copy instruction CopyMI. This returns
/// true if the copy was successfully coalesced away. If it is not
/// currently possible to coalesce this interval, but it may be possible if
/// other things get coalesced, then it returns true by reference in
/// 'Again'.
bool joinCopy(MachineInstr *TheCopy, bool &Again);
/// joinIntervals - Attempt to join these two intervals. On failure, this
/// returns false. The output "SrcInt" will not have been modified, so we
/// can use this information below to update aliases.
bool joinIntervals(CoalescerPair &CP);
/// Attempt joining two virtual registers. Return true on success.
bool joinVirtRegs(CoalescerPair &CP);
/// Attempt joining with a reserved physreg.
bool joinReservedPhysReg(CoalescerPair &CP);
/// adjustCopiesBackFrom - We found a non-trivially-coalescable copy. If
/// the source value number is defined by a copy from the destination reg
/// see if we can merge these two destination reg valno# into a single
/// value number, eliminating a copy.
bool adjustCopiesBackFrom(const CoalescerPair &CP, MachineInstr *CopyMI);
/// hasOtherReachingDefs - Return true if there are definitions of IntB
/// other than BValNo val# that can reach uses of AValno val# of IntA.
bool hasOtherReachingDefs(LiveInterval &IntA, LiveInterval &IntB,
VNInfo *AValNo, VNInfo *BValNo);
/// removeCopyByCommutingDef - We found a non-trivially-coalescable copy.
/// If the source value number is defined by a commutable instruction and
/// its other operand is coalesced to the copy dest register, see if we
/// can transform the copy into a noop by commuting the definition.
bool removeCopyByCommutingDef(const CoalescerPair &CP,MachineInstr *CopyMI);
/// reMaterializeTrivialDef - If the source of a copy is defined by a
/// trivial computation, replace the copy by rematerialize the definition.
bool reMaterializeTrivialDef(CoalescerPair &CP, MachineInstr *CopyMI,
bool &IsDefCopy);
/// canJoinPhys - Return true if a physreg copy should be joined.
bool canJoinPhys(const CoalescerPair &CP);
/// updateRegDefsUses - Replace all defs and uses of SrcReg to DstReg and
/// update the subregister number if it is not zero. If DstReg is a
/// physical register and the existing subregister number of the def / use
/// being updated is not zero, make sure to set it to the correct physical
/// subregister.
void updateRegDefsUses(unsigned SrcReg, unsigned DstReg, unsigned SubIdx);
/// eliminateUndefCopy - Handle copies of undef values.
bool eliminateUndefCopy(MachineInstr *CopyMI, const CoalescerPair &CP);
public:
static char ID; // Class identification, replacement for typeinfo
RegisterCoalescer() : MachineFunctionPass(ID) {
initializeRegisterCoalescerPass(*PassRegistry::getPassRegistry());
}
virtual void getAnalysisUsage(AnalysisUsage &AU) const;
virtual void releaseMemory();
/// runOnMachineFunction - pass entry point
virtual bool runOnMachineFunction(MachineFunction&);
/// print - Implement the dump method.
virtual void print(raw_ostream &O, const Module* = 0) const;
};
} /// end anonymous namespace
char &llvm::RegisterCoalescerID = RegisterCoalescer::ID;
INITIALIZE_PASS_BEGIN(RegisterCoalescer, "simple-register-coalescing",
"Simple Register Coalescing", false, false)
INITIALIZE_PASS_DEPENDENCY(LiveIntervals)
INITIALIZE_PASS_DEPENDENCY(SlotIndexes)
INITIALIZE_PASS_DEPENDENCY(MachineLoopInfo)
INITIALIZE_AG_DEPENDENCY(AliasAnalysis)
INITIALIZE_PASS_END(RegisterCoalescer, "simple-register-coalescing",
"Simple Register Coalescing", false, false)
char RegisterCoalescer::ID = 0;
static bool isMoveInstr(const TargetRegisterInfo &tri, const MachineInstr *MI,
unsigned &Src, unsigned &Dst,
unsigned &SrcSub, unsigned &DstSub) {
if (MI->isCopy()) {
Dst = MI->getOperand(0).getReg();
DstSub = MI->getOperand(0).getSubReg();
Src = MI->getOperand(1).getReg();
SrcSub = MI->getOperand(1).getSubReg();
} else if (MI->isSubregToReg()) {
Dst = MI->getOperand(0).getReg();
DstSub = tri.composeSubRegIndices(MI->getOperand(0).getSubReg(),
MI->getOperand(3).getImm());
Src = MI->getOperand(2).getReg();
SrcSub = MI->getOperand(2).getSubReg();
} else
return false;
return true;
}
// Return true if this block should be vacated by the coalescer to eliminate
// branches. The important cases to handle in the coalescer are critical edges
// split during phi elimination which contain only copies. Simple blocks that
// contain non-branches should also be vacated, but this can be handled by an
// earlier pass similar to early if-conversion.
static bool isSplitEdge(const MachineBasicBlock *MBB) {
if (MBB->pred_size() != 1 || MBB->succ_size() != 1)
return false;
for (MachineBasicBlock::const_iterator MII = MBB->begin(), E = MBB->end();
MII != E; ++MII) {
if (!MII->isCopyLike() && !MII->isUnconditionalBranch())
return false;
}
return true;
}
bool CoalescerPair::setRegisters(const MachineInstr *MI) {
SrcReg = DstReg = 0;
SrcIdx = DstIdx = 0;
NewRC = 0;
Flipped = CrossClass = false;
unsigned Src, Dst, SrcSub, DstSub;
if (!isMoveInstr(TRI, MI, Src, Dst, SrcSub, DstSub))
return false;
Partial = SrcSub || DstSub;
// If one register is a physreg, it must be Dst.
if (TargetRegisterInfo::isPhysicalRegister(Src)) {
if (TargetRegisterInfo::isPhysicalRegister(Dst))
return false;
std::swap(Src, Dst);
std::swap(SrcSub, DstSub);
Flipped = true;
}
const MachineRegisterInfo &MRI = MI->getParent()->getParent()->getRegInfo();
if (TargetRegisterInfo::isPhysicalRegister(Dst)) {
// Eliminate DstSub on a physreg.
if (DstSub) {
Dst = TRI.getSubReg(Dst, DstSub);
if (!Dst) return false;
DstSub = 0;
}
// Eliminate SrcSub by picking a corresponding Dst superregister.
if (SrcSub) {
Dst = TRI.getMatchingSuperReg(Dst, SrcSub, MRI.getRegClass(Src));
if (!Dst) return false;
SrcSub = 0;
} else if (!MRI.getRegClass(Src)->contains(Dst)) {
return false;
}
} else {
// Both registers are virtual.
const TargetRegisterClass *SrcRC = MRI.getRegClass(Src);
const TargetRegisterClass *DstRC = MRI.getRegClass(Dst);
// Both registers have subreg indices.
if (SrcSub && DstSub) {
// Copies between different sub-registers are never coalescable.
if (Src == Dst && SrcSub != DstSub)
return false;
NewRC = TRI.getCommonSuperRegClass(SrcRC, SrcSub, DstRC, DstSub,
SrcIdx, DstIdx);
if (!NewRC)
return false;
} else if (DstSub) {
// SrcReg will be merged with a sub-register of DstReg.
SrcIdx = DstSub;
NewRC = TRI.getMatchingSuperRegClass(DstRC, SrcRC, DstSub);
} else if (SrcSub) {
// DstReg will be merged with a sub-register of SrcReg.
DstIdx = SrcSub;
NewRC = TRI.getMatchingSuperRegClass(SrcRC, DstRC, SrcSub);
} else {
// This is a straight copy without sub-registers.
NewRC = TRI.getCommonSubClass(DstRC, SrcRC);
}
// The combined constraint may be impossible to satisfy.
if (!NewRC)
return false;
// Prefer SrcReg to be a sub-register of DstReg.
// FIXME: Coalescer should support subregs symmetrically.
if (DstIdx && !SrcIdx) {
std::swap(Src, Dst);
std::swap(SrcIdx, DstIdx);
Flipped = !Flipped;
}
CrossClass = NewRC != DstRC || NewRC != SrcRC;
}
// Check our invariants
assert(TargetRegisterInfo::isVirtualRegister(Src) && "Src must be virtual");
assert(!(TargetRegisterInfo::isPhysicalRegister(Dst) && DstSub) &&
"Cannot have a physical SubIdx");
SrcReg = Src;
DstReg = Dst;
return true;
}
bool CoalescerPair::flip() {
if (TargetRegisterInfo::isPhysicalRegister(DstReg))
return false;
std::swap(SrcReg, DstReg);
std::swap(SrcIdx, DstIdx);
Flipped = !Flipped;
return true;
}
bool CoalescerPair::isCoalescable(const MachineInstr *MI) const {
if (!MI)
return false;
unsigned Src, Dst, SrcSub, DstSub;
if (!isMoveInstr(TRI, MI, Src, Dst, SrcSub, DstSub))
return false;
// Find the virtual register that is SrcReg.
if (Dst == SrcReg) {
std::swap(Src, Dst);
std::swap(SrcSub, DstSub);
} else if (Src != SrcReg) {
return false;
}
// Now check that Dst matches DstReg.
if (TargetRegisterInfo::isPhysicalRegister(DstReg)) {
if (!TargetRegisterInfo::isPhysicalRegister(Dst))
return false;
assert(!DstIdx && !SrcIdx && "Inconsistent CoalescerPair state.");
// DstSub could be set for a physreg from INSERT_SUBREG.
if (DstSub)
Dst = TRI.getSubReg(Dst, DstSub);
// Full copy of Src.
if (!SrcSub)
return DstReg == Dst;
// This is a partial register copy. Check that the parts match.
return TRI.getSubReg(DstReg, SrcSub) == Dst;
} else {
// DstReg is virtual.
if (DstReg != Dst)
return false;
// Registers match, do the subregisters line up?
return TRI.composeSubRegIndices(SrcIdx, SrcSub) ==
TRI.composeSubRegIndices(DstIdx, DstSub);
}
}
void RegisterCoalescer::getAnalysisUsage(AnalysisUsage &AU) const {
AU.setPreservesCFG();
AU.addRequired<AliasAnalysis>();
AU.addRequired<LiveIntervals>();
AU.addPreserved<LiveIntervals>();
AU.addPreserved<SlotIndexes>();
AU.addRequired<MachineLoopInfo>();
AU.addPreserved<MachineLoopInfo>();
AU.addPreservedID(MachineDominatorsID);
MachineFunctionPass::getAnalysisUsage(AU);
}
void RegisterCoalescer::eliminateDeadDefs() {
SmallVector<LiveInterval*, 8> NewRegs;
LiveRangeEdit(0, NewRegs, *MF, *LIS, 0, this).eliminateDeadDefs(DeadDefs);
}
// Callback from eliminateDeadDefs().
void RegisterCoalescer::LRE_WillEraseInstruction(MachineInstr *MI) {
// MI may be in WorkList. Make sure we don't visit it.
ErasedInstrs.insert(MI);
}
/// adjustCopiesBackFrom - We found a non-trivially-coalescable copy with IntA
/// being the source and IntB being the dest, thus this defines a value number
/// in IntB. If the source value number (in IntA) is defined by a copy from B,
/// see if we can merge these two pieces of B into a single value number,
/// eliminating a copy. For example:
///
/// A3 = B0
/// ...
/// B1 = A3 <- this copy
///
/// In this case, B0 can be extended to where the B1 copy lives, allowing the B1
/// value number to be replaced with B0 (which simplifies the B liveinterval).
///
/// This returns true if an interval was modified.
///
bool RegisterCoalescer::adjustCopiesBackFrom(const CoalescerPair &CP,
MachineInstr *CopyMI) {
assert(!CP.isPartial() && "This doesn't work for partial copies.");
assert(!CP.isPhys() && "This doesn't work for physreg copies.");
LiveInterval &IntA =
LIS->getInterval(CP.isFlipped() ? CP.getDstReg() : CP.getSrcReg());
LiveInterval &IntB =
LIS->getInterval(CP.isFlipped() ? CP.getSrcReg() : CP.getDstReg());
SlotIndex CopyIdx = LIS->getInstructionIndex(CopyMI).getRegSlot();
// BValNo is a value number in B that is defined by a copy from A. 'B3' in
// the example above.
LiveInterval::iterator BLR = IntB.FindLiveRangeContaining(CopyIdx);
if (BLR == IntB.end()) return false;
VNInfo *BValNo = BLR->valno;
// Get the location that B is defined at. Two options: either this value has
// an unknown definition point or it is defined at CopyIdx. If unknown, we
// can't process it.
if (BValNo->def != CopyIdx) return false;
// AValNo is the value number in A that defines the copy, A3 in the example.
SlotIndex CopyUseIdx = CopyIdx.getRegSlot(true);
LiveInterval::iterator ALR = IntA.FindLiveRangeContaining(CopyUseIdx);
// The live range might not exist after fun with physreg coalescing.
if (ALR == IntA.end()) return false;
VNInfo *AValNo = ALR->valno;
// If AValNo is defined as a copy from IntB, we can potentially process this.
// Get the instruction that defines this value number.
MachineInstr *ACopyMI = LIS->getInstructionFromIndex(AValNo->def);
// Don't allow any partial copies, even if isCoalescable() allows them.
if (!CP.isCoalescable(ACopyMI) || !ACopyMI->isFullCopy())
return false;
// Get the LiveRange in IntB that this value number starts with.
LiveInterval::iterator ValLR =
IntB.FindLiveRangeContaining(AValNo->def.getPrevSlot());
if (ValLR == IntB.end())
return false;
// Make sure that the end of the live range is inside the same block as
// CopyMI.
MachineInstr *ValLREndInst =
LIS->getInstructionFromIndex(ValLR->end.getPrevSlot());
if (!ValLREndInst || ValLREndInst->getParent() != CopyMI->getParent())
return false;
// Okay, we now know that ValLR ends in the same block that the CopyMI
// live-range starts. If there are no intervening live ranges between them in
// IntB, we can merge them.
if (ValLR+1 != BLR) return false;
DEBUG(dbgs() << "Extending: " << PrintReg(IntB.reg, TRI));
SlotIndex FillerStart = ValLR->end, FillerEnd = BLR->start;
// We are about to delete CopyMI, so need to remove it as the 'instruction
// that defines this value #'. Update the valnum with the new defining
// instruction #.
BValNo->def = FillerStart;
// Okay, we can merge them. We need to insert a new liverange:
// [ValLR.end, BLR.begin) of either value number, then we merge the
// two value numbers.
IntB.addRange(LiveRange(FillerStart, FillerEnd, BValNo));
// Okay, merge "B1" into the same value number as "B0".
if (BValNo != ValLR->valno)
IntB.MergeValueNumberInto(BValNo, ValLR->valno);
DEBUG(dbgs() << " result = " << IntB << '\n');
// If the source instruction was killing the source register before the
// merge, unset the isKill marker given the live range has been extended.
int UIdx = ValLREndInst->findRegisterUseOperandIdx(IntB.reg, true);
if (UIdx != -1) {
ValLREndInst->getOperand(UIdx).setIsKill(false);
}
// Rewrite the copy. If the copy instruction was killing the destination
// register before the merge, find the last use and trim the live range. That
// will also add the isKill marker.
CopyMI->substituteRegister(IntA.reg, IntB.reg, 0, *TRI);
if (ALR->end == CopyIdx)
LIS->shrinkToUses(&IntA);
++numExtends;
return true;
}
/// hasOtherReachingDefs - Return true if there are definitions of IntB
/// other than BValNo val# that can reach uses of AValno val# of IntA.
bool RegisterCoalescer::hasOtherReachingDefs(LiveInterval &IntA,
LiveInterval &IntB,
VNInfo *AValNo,
VNInfo *BValNo) {
// If AValNo has PHI kills, conservatively assume that IntB defs can reach
// the PHI values.
if (LIS->hasPHIKill(IntA, AValNo))
return true;
for (LiveInterval::iterator AI = IntA.begin(), AE = IntA.end();
AI != AE; ++AI) {
if (AI->valno != AValNo) continue;
LiveInterval::Ranges::iterator BI =
std::upper_bound(IntB.ranges.begin(), IntB.ranges.end(), AI->start);
if (BI != IntB.ranges.begin())
--BI;
for (; BI != IntB.ranges.end() && AI->end >= BI->start; ++BI) {
if (BI->valno == BValNo)
continue;
if (BI->start <= AI->start && BI->end > AI->start)
return true;
if (BI->start > AI->start && BI->start < AI->end)
return true;
}
}
return false;
}
/// removeCopyByCommutingDef - We found a non-trivially-coalescable copy with
/// IntA being the source and IntB being the dest, thus this defines a value
/// number in IntB. If the source value number (in IntA) is defined by a
/// commutable instruction and its other operand is coalesced to the copy dest
/// register, see if we can transform the copy into a noop by commuting the
/// definition. For example,
///
/// A3 = op A2 B0<kill>
/// ...
/// B1 = A3 <- this copy
/// ...
/// = op A3 <- more uses
///
/// ==>
///
/// B2 = op B0 A2<kill>
/// ...
/// B1 = B2 <- now an identify copy
/// ...
/// = op B2 <- more uses
///
/// This returns true if an interval was modified.
///
bool RegisterCoalescer::removeCopyByCommutingDef(const CoalescerPair &CP,
MachineInstr *CopyMI) {
assert (!CP.isPhys());
SlotIndex CopyIdx = LIS->getInstructionIndex(CopyMI).getRegSlot();
LiveInterval &IntA =
LIS->getInterval(CP.isFlipped() ? CP.getDstReg() : CP.getSrcReg());
LiveInterval &IntB =
LIS->getInterval(CP.isFlipped() ? CP.getSrcReg() : CP.getDstReg());
// BValNo is a value number in B that is defined by a copy from A. 'B3' in
// the example above.
VNInfo *BValNo = IntB.getVNInfoAt(CopyIdx);
if (!BValNo || BValNo->def != CopyIdx)
return false;
assert(BValNo->def == CopyIdx && "Copy doesn't define the value?");
// AValNo is the value number in A that defines the copy, A3 in the example.
VNInfo *AValNo = IntA.getVNInfoAt(CopyIdx.getRegSlot(true));
assert(AValNo && "COPY source not live");
if (AValNo->isPHIDef() || AValNo->isUnused())
return false;
MachineInstr *DefMI = LIS->getInstructionFromIndex(AValNo->def);
if (!DefMI)
return false;
if (!DefMI->isCommutable())
return false;
// If DefMI is a two-address instruction then commuting it will change the
// destination register.
int DefIdx = DefMI->findRegisterDefOperandIdx(IntA.reg);
assert(DefIdx != -1);
unsigned UseOpIdx;
if (!DefMI->isRegTiedToUseOperand(DefIdx, &UseOpIdx))
return false;
unsigned Op1, Op2, NewDstIdx;
if (!TII->findCommutedOpIndices(DefMI, Op1, Op2))
return false;
if (Op1 == UseOpIdx)
NewDstIdx = Op2;
else if (Op2 == UseOpIdx)
NewDstIdx = Op1;
else
return false;
MachineOperand &NewDstMO = DefMI->getOperand(NewDstIdx);
unsigned NewReg = NewDstMO.getReg();
if (NewReg != IntB.reg || !LiveRangeQuery(IntB, AValNo->def).isKill())
return false;
// Make sure there are no other definitions of IntB that would reach the
// uses which the new definition can reach.
if (hasOtherReachingDefs(IntA, IntB, AValNo, BValNo))
return false;
// If some of the uses of IntA.reg is already coalesced away, return false.
// It's not possible to determine whether it's safe to perform the coalescing.
for (MachineRegisterInfo::use_nodbg_iterator UI =
MRI->use_nodbg_begin(IntA.reg),
UE = MRI->use_nodbg_end(); UI != UE; ++UI) {
MachineInstr *UseMI = &*UI;
SlotIndex UseIdx = LIS->getInstructionIndex(UseMI);
LiveInterval::iterator ULR = IntA.FindLiveRangeContaining(UseIdx);
if (ULR == IntA.end() || ULR->valno != AValNo)
continue;
// If this use is tied to a def, we can't rewrite the register.
if (UseMI->isRegTiedToDefOperand(UI.getOperandNo()))
return false;
}
DEBUG(dbgs() << "\tremoveCopyByCommutingDef: " << AValNo->def << '\t'
<< *DefMI);
// At this point we have decided that it is legal to do this
// transformation. Start by commuting the instruction.
MachineBasicBlock *MBB = DefMI->getParent();
MachineInstr *NewMI = TII->commuteInstruction(DefMI);
if (!NewMI)
return false;
if (TargetRegisterInfo::isVirtualRegister(IntA.reg) &&
TargetRegisterInfo::isVirtualRegister(IntB.reg) &&
!MRI->constrainRegClass(IntB.reg, MRI->getRegClass(IntA.reg)))
return false;
if (NewMI != DefMI) {
LIS->ReplaceMachineInstrInMaps(DefMI, NewMI);
MachineBasicBlock::iterator Pos = DefMI;
MBB->insert(Pos, NewMI);
MBB->erase(DefMI);
}
unsigned OpIdx = NewMI->findRegisterUseOperandIdx(IntA.reg, false);
NewMI->getOperand(OpIdx).setIsKill();
// If ALR and BLR overlaps and end of BLR extends beyond end of ALR, e.g.
// A = or A, B
// ...
// B = A
// ...
// C = A<kill>
// ...
// = B
// Update uses of IntA of the specific Val# with IntB.
for (MachineRegisterInfo::use_iterator UI = MRI->use_begin(IntA.reg),
UE = MRI->use_end(); UI != UE;) {
MachineOperand &UseMO = UI.getOperand();
MachineInstr *UseMI = &*UI;
++UI;
if (UseMI->isDebugValue()) {
// FIXME These don't have an instruction index. Not clear we have enough
// info to decide whether to do this replacement or not. For now do it.
UseMO.setReg(NewReg);
continue;
}
SlotIndex UseIdx = LIS->getInstructionIndex(UseMI).getRegSlot(true);
LiveInterval::iterator ULR = IntA.FindLiveRangeContaining(UseIdx);
if (ULR == IntA.end() || ULR->valno != AValNo)
continue;
// Kill flags are no longer accurate. They are recomputed after RA.
UseMO.setIsKill(false);
if (TargetRegisterInfo::isPhysicalRegister(NewReg))
UseMO.substPhysReg(NewReg, *TRI);
else
UseMO.setReg(NewReg);
if (UseMI == CopyMI)
continue;
if (!UseMI->isCopy())
continue;
if (UseMI->getOperand(0).getReg() != IntB.reg ||
UseMI->getOperand(0).getSubReg())
continue;
// This copy will become a noop. If it's defining a new val#, merge it into
// BValNo.
SlotIndex DefIdx = UseIdx.getRegSlot();
VNInfo *DVNI = IntB.getVNInfoAt(DefIdx);
if (!DVNI)
continue;
DEBUG(dbgs() << "\t\tnoop: " << DefIdx << '\t' << *UseMI);
assert(DVNI->def == DefIdx);
BValNo = IntB.MergeValueNumberInto(BValNo, DVNI);
ErasedInstrs.insert(UseMI);
LIS->RemoveMachineInstrFromMaps(UseMI);
UseMI->eraseFromParent();
}
// Extend BValNo by merging in IntA live ranges of AValNo. Val# definition
// is updated.
VNInfo *ValNo = BValNo;
ValNo->def = AValNo->def;
for (LiveInterval::iterator AI = IntA.begin(), AE = IntA.end();
AI != AE; ++AI) {
if (AI->valno != AValNo) continue;
IntB.addRange(LiveRange(AI->start, AI->end, ValNo));
}
DEBUG(dbgs() << "\t\textended: " << IntB << '\n');
IntA.removeValNo(AValNo);
DEBUG(dbgs() << "\t\ttrimmed: " << IntA << '\n');
++numCommutes;
return true;
}
/// reMaterializeTrivialDef - If the source of a copy is defined by a trivial
/// computation, replace the copy by rematerialize the definition.
bool RegisterCoalescer::reMaterializeTrivialDef(CoalescerPair &CP,
MachineInstr *CopyMI,
bool &IsDefCopy) {
IsDefCopy = false;
unsigned SrcReg = CP.isFlipped() ? CP.getDstReg() : CP.getSrcReg();
unsigned SrcIdx = CP.isFlipped() ? CP.getDstIdx() : CP.getSrcIdx();
unsigned DstReg = CP.isFlipped() ? CP.getSrcReg() : CP.getDstReg();
unsigned DstIdx = CP.isFlipped() ? CP.getSrcIdx() : CP.getDstIdx();
if (TargetRegisterInfo::isPhysicalRegister(SrcReg))
return false;
LiveInterval &SrcInt = LIS->getInterval(SrcReg);
SlotIndex CopyIdx = LIS->getInstructionIndex(CopyMI);
VNInfo *ValNo = LiveRangeQuery(SrcInt, CopyIdx).valueIn();
assert(ValNo && "CopyMI input register not live");
if (ValNo->isPHIDef() || ValNo->isUnused())
return false;
MachineInstr *DefMI = LIS->getInstructionFromIndex(ValNo->def);
if (!DefMI)
return false;
if (DefMI->isCopyLike()) {
IsDefCopy = true;
return false;
}
if (!DefMI->isAsCheapAsAMove())
return false;
if (!TII->isTriviallyReMaterializable(DefMI, AA))
return false;
bool SawStore = false;
if (!DefMI->isSafeToMove(TII, AA, SawStore))
return false;
const MCInstrDesc &MCID = DefMI->getDesc();
if (MCID.getNumDefs() != 1)
return false;
// Only support subregister destinations when the def is read-undef.
MachineOperand &DstOperand = CopyMI->getOperand(0);
unsigned CopyDstReg = DstOperand.getReg();
if (DstOperand.getSubReg() && !DstOperand.isUndef())
return false;
const TargetRegisterClass *DefRC = TII->getRegClass(MCID, 0, TRI, *MF);
if (!DefMI->isImplicitDef()) {
if (TargetRegisterInfo::isPhysicalRegister(DstReg)) {
unsigned NewDstReg = DstReg;
unsigned NewDstIdx = TRI->composeSubRegIndices(CP.getSrcIdx(),
DefMI->getOperand(0).getSubReg());
if (NewDstIdx)
NewDstReg = TRI->getSubReg(DstReg, NewDstIdx);
// Finally, make sure that the physical subregister that will be
// constructed later is permitted for the instruction.
if (!DefRC->contains(NewDstReg))
return false;
} else {
// Theoretically, some stack frame reference could exist. Just make sure
// it hasn't actually happened.
assert(TargetRegisterInfo::isVirtualRegister(DstReg) &&
"Only expect to deal with virtual or physical registers");
}
}
MachineBasicBlock *MBB = CopyMI->getParent();
MachineBasicBlock::iterator MII =
llvm::next(MachineBasicBlock::iterator(CopyMI));
TII->reMaterialize(*MBB, MII, DstReg, SrcIdx, DefMI, *TRI);
MachineInstr *NewMI = prior(MII);
LIS->ReplaceMachineInstrInMaps(CopyMI, NewMI);
CopyMI->eraseFromParent();
ErasedInstrs.insert(CopyMI);
// NewMI may have dead implicit defs (E.g. EFLAGS for MOV<bits>r0 on X86).
// We need to remember these so we can add intervals once we insert
// NewMI into SlotIndexes.
SmallVector<unsigned, 4> NewMIImplDefs;
for (unsigned i = NewMI->getDesc().getNumOperands(),
e = NewMI->getNumOperands(); i != e; ++i) {
MachineOperand &MO = NewMI->getOperand(i);
if (MO.isReg()) {
assert(MO.isDef() && MO.isImplicit() && MO.isDead() &&
TargetRegisterInfo::isPhysicalRegister(MO.getReg()));
NewMIImplDefs.push_back(MO.getReg());
}
}
if (TargetRegisterInfo::isVirtualRegister(DstReg)) {
unsigned NewIdx = NewMI->getOperand(0).getSubReg();
const TargetRegisterClass *RCForInst;
if (NewIdx)
RCForInst = TRI->getMatchingSuperRegClass(MRI->getRegClass(DstReg), DefRC,
NewIdx);
if (MRI->constrainRegClass(DstReg, DefRC)) {
// The materialized instruction is quite capable of setting DstReg
// directly, but it may still have a now-trivial subregister index which
// we should clear.
NewMI->getOperand(0).setSubReg(0);
} else if (NewIdx && RCForInst) {
// The subreg index on NewMI is essential; we still have to make sure
// DstReg:idx is in a class that NewMI can use.
MRI->constrainRegClass(DstReg, RCForInst);
} else {
// DstReg is actually incompatible with NewMI, we have to move to a
// super-reg's class. This could come from a sequence like:
// GR32 = MOV32r0
// GR8 = COPY GR32:sub_8
MRI->setRegClass(DstReg, CP.getNewRC());
updateRegDefsUses(DstReg, DstReg, DstIdx);
NewMI->getOperand(0).setSubReg(
TRI->composeSubRegIndices(SrcIdx, DefMI->getOperand(0).getSubReg()));
}
} else if (NewMI->getOperand(0).getReg() != CopyDstReg) {
// The New instruction may be defining a sub-register of what's actually
// been asked for. If so it must implicitly define the whole thing.
assert(TargetRegisterInfo::isPhysicalRegister(DstReg) &&
"Only expect virtual or physical registers in remat");
NewMI->getOperand(0).setIsDead(true);
NewMI->addOperand(MachineOperand::CreateReg(CopyDstReg,
true /*IsDef*/,
true /*IsImp*/,
false /*IsKill*/));
}
if (NewMI->getOperand(0).getSubReg())
NewMI->getOperand(0).setIsUndef();
// CopyMI may have implicit operands, transfer them over to the newly
// rematerialized instruction. And update implicit def interval valnos.
for (unsigned i = CopyMI->getDesc().getNumOperands(),
e = CopyMI->getNumOperands(); i != e; ++i) {
MachineOperand &MO = CopyMI->getOperand(i);
if (MO.isReg()) {
assert(MO.isImplicit() && "No explicit operands after implict operands.");
// Discard VReg implicit defs.
if (TargetRegisterInfo::isPhysicalRegister(MO.getReg())) {
NewMI->addOperand(MO);
}
}
}
SlotIndex NewMIIdx = LIS->getInstructionIndex(NewMI);
for (unsigned i = 0, e = NewMIImplDefs.size(); i != e; ++i) {
unsigned Reg = NewMIImplDefs[i];
for (MCRegUnitIterator Units(Reg, TRI); Units.isValid(); ++Units)
if (LiveInterval *LI = LIS->getCachedRegUnit(*Units))
LI->createDeadDef(NewMIIdx.getRegSlot(), LIS->getVNInfoAllocator());
}
DEBUG(dbgs() << "Remat: " << *NewMI);
++NumReMats;
// The source interval can become smaller because we removed a use.
LIS->shrinkToUses(&SrcInt, &DeadDefs);
if (!DeadDefs.empty())
eliminateDeadDefs();
return true;
}
/// eliminateUndefCopy - ProcessImpicitDefs may leave some copies of <undef>
/// values, it only removes local variables. When we have a copy like:
///
/// %vreg1 = COPY %vreg2<undef>
///
/// We delete the copy and remove the corresponding value number from %vreg1.
/// Any uses of that value number are marked as <undef>.
bool RegisterCoalescer::eliminateUndefCopy(MachineInstr *CopyMI,
const CoalescerPair &CP) {
SlotIndex Idx = LIS->getInstructionIndex(CopyMI);
LiveInterval *SrcInt = &LIS->getInterval(CP.getSrcReg());
if (SrcInt->liveAt(Idx))
return false;
LiveInterval *DstInt = &LIS->getInterval(CP.getDstReg());
if (DstInt->liveAt(Idx))
return false;
// No intervals are live-in to CopyMI - it is undef.
if (CP.isFlipped())
DstInt = SrcInt;
SrcInt = 0;
VNInfo *DeadVNI = DstInt->getVNInfoAt(Idx.getRegSlot());
assert(DeadVNI && "No value defined in DstInt");
DstInt->removeValNo(DeadVNI);
// Find new undef uses.
for (MachineRegisterInfo::reg_nodbg_iterator
I = MRI->reg_nodbg_begin(DstInt->reg), E = MRI->reg_nodbg_end();
I != E; ++I) {
MachineOperand &MO = I.getOperand();
if (MO.isDef() || MO.isUndef())
continue;
MachineInstr *MI = MO.getParent();
SlotIndex Idx = LIS->getInstructionIndex(MI);
if (DstInt->liveAt(Idx))
continue;
MO.setIsUndef(true);
DEBUG(dbgs() << "\tnew undef: " << Idx << '\t' << *MI);
}
return true;
}
/// updateRegDefsUses - Replace all defs and uses of SrcReg to DstReg and
/// update the subregister number if it is not zero. If DstReg is a
/// physical register and the existing subregister number of the def / use
/// being updated is not zero, make sure to set it to the correct physical
/// subregister.
void RegisterCoalescer::updateRegDefsUses(unsigned SrcReg,
unsigned DstReg,
unsigned SubIdx) {
bool DstIsPhys = TargetRegisterInfo::isPhysicalRegister(DstReg);
LiveInterval *DstInt = DstIsPhys ? 0 : &LIS->getInterval(DstReg);
SmallPtrSet<MachineInstr*, 8> Visited;
for (MachineRegisterInfo::reg_iterator I = MRI->reg_begin(SrcReg);
MachineInstr *UseMI = I.skipInstruction();) {
// Each instruction can only be rewritten once because sub-register
// composition is not always idempotent. When SrcReg != DstReg, rewriting
// the UseMI operands removes them from the SrcReg use-def chain, but when
// SrcReg is DstReg we could encounter UseMI twice if it has multiple
// operands mentioning the virtual register.
if (SrcReg == DstReg && !Visited.insert(UseMI))
continue;
SmallVector<unsigned,8> Ops;
bool Reads, Writes;
tie(Reads, Writes) = UseMI->readsWritesVirtualRegister(SrcReg, &Ops);
// If SrcReg wasn't read, it may still be the case that DstReg is live-in
// because SrcReg is a sub-register.
if (DstInt && !Reads && SubIdx)
Reads = DstInt->liveAt(LIS->getInstructionIndex(UseMI));
// Replace SrcReg with DstReg in all UseMI operands.
for (unsigned i = 0, e = Ops.size(); i != e; ++i) {
MachineOperand &MO = UseMI->getOperand(Ops[i]);
// Adjust <undef> flags in case of sub-register joins. We don't want to
// turn a full def into a read-modify-write sub-register def and vice
// versa.
if (SubIdx && MO.isDef())
MO.setIsUndef(!Reads);
if (DstIsPhys)
MO.substPhysReg(DstReg, *TRI);
else
MO.substVirtReg(DstReg, SubIdx, *TRI);
}
DEBUG({
dbgs() << "\t\tupdated: ";
if (!UseMI->isDebugValue())
dbgs() << LIS->getInstructionIndex(UseMI) << "\t";
dbgs() << *UseMI;
});
}
}
/// canJoinPhys - Return true if a copy involving a physreg should be joined.
bool RegisterCoalescer::canJoinPhys(const CoalescerPair &CP) {
/// Always join simple intervals that are defined by a single copy from a
/// reserved register. This doesn't increase register pressure, so it is
/// always beneficial.
if (!MRI->isReserved(CP.getDstReg())) {
DEBUG(dbgs() << "\tCan only merge into reserved registers.\n");
return false;
}
LiveInterval &JoinVInt = LIS->getInterval(CP.getSrcReg());
if (CP.isFlipped() && JoinVInt.containsOneValue())
return true;
DEBUG(dbgs() << "\tCannot join defs into reserved register.\n");
return false;
}
/// joinCopy - Attempt to join intervals corresponding to SrcReg/DstReg,
/// which are the src/dst of the copy instruction CopyMI. This returns true
/// if the copy was successfully coalesced away. If it is not currently
/// possible to coalesce this interval, but it may be possible if other
/// things get coalesced, then it returns true by reference in 'Again'.
bool RegisterCoalescer::joinCopy(MachineInstr *CopyMI, bool &Again) {
Again = false;
DEBUG(dbgs() << LIS->getInstructionIndex(CopyMI) << '\t' << *CopyMI);
CoalescerPair CP(*TRI);
if (!CP.setRegisters(CopyMI)) {
DEBUG(dbgs() << "\tNot coalescable.\n");
return false;
}
// Dead code elimination. This really should be handled by MachineDCE, but
// sometimes dead copies slip through, and we can't generate invalid live
// ranges.
if (!CP.isPhys() && CopyMI->allDefsAreDead()) {
DEBUG(dbgs() << "\tCopy is dead.\n");
DeadDefs.push_back(CopyMI);
eliminateDeadDefs();
return true;
}
// Eliminate undefs.
if (!CP.isPhys() && eliminateUndefCopy(CopyMI, CP)) {
DEBUG(dbgs() << "\tEliminated copy of <undef> value.\n");
LIS->RemoveMachineInstrFromMaps(CopyMI);
CopyMI->eraseFromParent();
return false; // Not coalescable.
}
// Coalesced copies are normally removed immediately, but transformations
// like removeCopyByCommutingDef() can inadvertently create identity copies.
// When that happens, just join the values and remove the copy.
if (CP.getSrcReg() == CP.getDstReg()) {
LiveInterval &LI = LIS->getInterval(CP.getSrcReg());
DEBUG(dbgs() << "\tCopy already coalesced: " << LI << '\n');
LiveRangeQuery LRQ(LI, LIS->getInstructionIndex(CopyMI));
if (VNInfo *DefVNI = LRQ.valueDefined()) {
VNInfo *ReadVNI = LRQ.valueIn();
assert(ReadVNI && "No value before copy and no <undef> flag.");
assert(ReadVNI != DefVNI && "Cannot read and define the same value.");
LI.MergeValueNumberInto(DefVNI, ReadVNI);
DEBUG(dbgs() << "\tMerged values: " << LI << '\n');
}
LIS->RemoveMachineInstrFromMaps(CopyMI);
CopyMI->eraseFromParent();
return true;
}
// Enforce policies.
if (CP.isPhys()) {
DEBUG(dbgs() << "\tConsidering merging " << PrintReg(CP.getSrcReg(), TRI)
<< " with " << PrintReg(CP.getDstReg(), TRI, CP.getSrcIdx())
<< '\n');
if (!canJoinPhys(CP)) {
// Before giving up coalescing, if definition of source is defined by
// trivial computation, try rematerializing it.
bool IsDefCopy;
if (reMaterializeTrivialDef(CP, CopyMI, IsDefCopy))
return true;
if (IsDefCopy)
Again = true; // May be possible to coalesce later.
return false;
}
} else {
DEBUG({
dbgs() << "\tConsidering merging to " << CP.getNewRC()->getName()
<< " with ";
if (CP.getDstIdx() && CP.getSrcIdx())
dbgs() << PrintReg(CP.getDstReg()) << " in "
<< TRI->getSubRegIndexName(CP.getDstIdx()) << " and "
<< PrintReg(CP.getSrcReg()) << " in "
<< TRI->getSubRegIndexName(CP.getSrcIdx()) << '\n';
else
dbgs() << PrintReg(CP.getSrcReg(), TRI) << " in "
<< PrintReg(CP.getDstReg(), TRI, CP.getSrcIdx()) << '\n';
});
// When possible, let DstReg be the larger interval.
if (!CP.isPartial() && LIS->getInterval(CP.getSrcReg()).ranges.size() >
LIS->getInterval(CP.getDstReg()).ranges.size())
CP.flip();
}
// Okay, attempt to join these two intervals. On failure, this returns false.
// Otherwise, if one of the intervals being joined is a physreg, this method
// always canonicalizes DstInt to be it. The output "SrcInt" will not have
// been modified, so we can use this information below to update aliases.
if (!joinIntervals(CP)) {
// Coalescing failed.
// If definition of source is defined by trivial computation, try
// rematerializing it.
bool IsDefCopy;
if (reMaterializeTrivialDef(CP, CopyMI, IsDefCopy))
return true;
// If we can eliminate the copy without merging the live ranges, do so now.
if (!CP.isPartial() && !CP.isPhys()) {
if (adjustCopiesBackFrom(CP, CopyMI) ||
removeCopyByCommutingDef(CP, CopyMI)) {
LIS->RemoveMachineInstrFromMaps(CopyMI);
CopyMI->eraseFromParent();
DEBUG(dbgs() << "\tTrivial!\n");
return true;
}
}
// Otherwise, we are unable to join the intervals.
DEBUG(dbgs() << "\tInterference!\n");
Again = true; // May be possible to coalesce later.
return false;
}
// Coalescing to a virtual register that is of a sub-register class of the
// other. Make sure the resulting register is set to the right register class.
if (CP.isCrossClass()) {
++numCrossRCs;
MRI->setRegClass(CP.getDstReg(), CP.getNewRC());
}
// Removing sub-register copies can ease the register class constraints.
// Make sure we attempt to inflate the register class of DstReg.
if (!CP.isPhys() && RegClassInfo.isProperSubClass(CP.getNewRC()))
InflateRegs.push_back(CP.getDstReg());
// CopyMI has been erased by joinIntervals at this point. Remove it from
// ErasedInstrs since copyCoalesceWorkList() won't add a successful join back
// to the work list. This keeps ErasedInstrs from growing needlessly.
ErasedInstrs.erase(CopyMI);
// Rewrite all SrcReg operands to DstReg.
// Also update DstReg operands to include DstIdx if it is set.
if (CP.getDstIdx())
updateRegDefsUses(CP.getDstReg(), CP.getDstReg(), CP.getDstIdx());
updateRegDefsUses(CP.getSrcReg(), CP.getDstReg(), CP.getSrcIdx());
// SrcReg is guaranteed to be the register whose live interval that is
// being merged.
LIS->removeInterval(CP.getSrcReg());
// Update regalloc hint.
TRI->UpdateRegAllocHint(CP.getSrcReg(), CP.getDstReg(), *MF);
DEBUG({
dbgs() << "\tJoined. Result = " << PrintReg(CP.getDstReg(), TRI);
if (!CP.isPhys())
dbgs() << LIS->getInterval(CP.getDstReg());
dbgs() << '\n';
});
++numJoins;
return true;
}
/// Attempt joining with a reserved physreg.
bool RegisterCoalescer::joinReservedPhysReg(CoalescerPair &CP) {
assert(CP.isPhys() && "Must be a physreg copy");
assert(MRI->isReserved(CP.getDstReg()) && "Not a reserved register");
LiveInterval &RHS = LIS->getInterval(CP.getSrcReg());
DEBUG(dbgs() << "\t\tRHS = " << PrintReg(CP.getSrcReg()) << ' ' << RHS
<< '\n');
assert(CP.isFlipped() && RHS.containsOneValue() &&
"Invalid join with reserved register");
// Optimization for reserved registers like ESP. We can only merge with a
// reserved physreg if RHS has a single value that is a copy of CP.DstReg().
// The live range of the reserved register will look like a set of dead defs
// - we don't properly track the live range of reserved registers.
// Deny any overlapping intervals. This depends on all the reserved
// register live ranges to look like dead defs.
for (MCRegUnitIterator UI(CP.getDstReg(), TRI); UI.isValid(); ++UI)
if (RHS.overlaps(LIS->getRegUnit(*UI))) {
DEBUG(dbgs() << "\t\tInterference: " << PrintRegUnit(*UI, TRI) << '\n');
return false;
}
// Skip any value computations, we are not adding new values to the
// reserved register. Also skip merging the live ranges, the reserved
// register live range doesn't need to be accurate as long as all the
// defs are there.
// Delete the identity copy.
MachineInstr *CopyMI = MRI->getVRegDef(RHS.reg);
LIS->RemoveMachineInstrFromMaps(CopyMI);
CopyMI->eraseFromParent();
// We don't track kills for reserved registers.
MRI->clearKillFlags(CP.getSrcReg());
return true;
}
//===----------------------------------------------------------------------===//
// Interference checking and interval joining
//===----------------------------------------------------------------------===//
//
// In the easiest case, the two live ranges being joined are disjoint, and
// there is no interference to consider. It is quite common, though, to have
// overlapping live ranges, and we need to check if the interference can be
// resolved.
//
// The live range of a single SSA value forms a sub-tree of the dominator tree.
// This means that two SSA values overlap if and only if the def of one value
// is contained in the live range of the other value. As a special case, the
// overlapping values can be defined at the same index.
//
// The interference from an overlapping def can be resolved in these cases:
//
// 1. Coalescable copies. The value is defined by a copy that would become an
// identity copy after joining SrcReg and DstReg. The copy instruction will
// be removed, and the value will be merged with the source value.
//
// There can be several copies back and forth, causing many values to be
// merged into one. We compute a list of ultimate values in the joined live
// range as well as a mappings from the old value numbers.
//
// 2. IMPLICIT_DEF. This instruction is only inserted to ensure all PHI
// predecessors have a live out value. It doesn't cause real interference,
// and can be merged into the value it overlaps. Like a coalescable copy, it
// can be erased after joining.
//
// 3. Copy of external value. The overlapping def may be a copy of a value that
// is already in the other register. This is like a coalescable copy, but
// the live range of the source register must be trimmed after erasing the
// copy instruction:
//
// %src = COPY %ext
// %dst = COPY %ext <-- Remove this COPY, trim the live range of %ext.
//
// 4. Clobbering undefined lanes. Vector registers are sometimes built by
// defining one lane at a time:
//
// %dst:ssub0<def,read-undef> = FOO
// %src = BAR
// %dst:ssub1<def> = COPY %src
//
// The live range of %src overlaps the %dst value defined by FOO, but
// merging %src into %dst:ssub1 is only going to clobber the ssub1 lane
// which was undef anyway.
//
// The value mapping is more complicated in this case. The final live range
// will have different value numbers for both FOO and BAR, but there is no
// simple mapping from old to new values. It may even be necessary to add
// new PHI values.
//
// 5. Clobbering dead lanes. A def may clobber a lane of a vector register that
// is live, but never read. This can happen because we don't compute
// individual live ranges per lane.
//
// %dst<def> = FOO
// %src = BAR
// %dst:ssub1<def> = COPY %src
//
// This kind of interference is only resolved locally. If the clobbered
// lane value escapes the block, the join is aborted.
namespace {
/// Track information about values in a single virtual register about to be
/// joined. Objects of this class are always created in pairs - one for each
/// side of the CoalescerPair.
class JoinVals {
LiveInterval &LI;
// Location of this register in the final joined register.
// Either CP.DstIdx or CP.SrcIdx.
unsigned SubIdx;
// Values that will be present in the final live range.
SmallVectorImpl<VNInfo*> &NewVNInfo;
const CoalescerPair &CP;
LiveIntervals *LIS;
SlotIndexes *Indexes;
const TargetRegisterInfo *TRI;
// Value number assignments. Maps value numbers in LI to entries in NewVNInfo.
// This is suitable for passing to LiveInterval::join().
SmallVector<int, 8> Assignments;
// Conflict resolution for overlapping values.
enum ConflictResolution {
// No overlap, simply keep this value.
CR_Keep,
// Merge this value into OtherVNI and erase the defining instruction.
// Used for IMPLICIT_DEF, coalescable copies, and copies from external
// values.
CR_Erase,
// Merge this value into OtherVNI but keep the defining instruction.
// This is for the special case where OtherVNI is defined by the same
// instruction.
CR_Merge,
// Keep this value, and have it replace OtherVNI where possible. This
// complicates value mapping since OtherVNI maps to two different values
// before and after this def.
// Used when clobbering undefined or dead lanes.
CR_Replace,
// Unresolved conflict. Visit later when all values have been mapped.
CR_Unresolved,
// Unresolvable conflict. Abort the join.
CR_Impossible
};
// Per-value info for LI. The lane bit masks are all relative to the final
// joined register, so they can be compared directly between SrcReg and
// DstReg.
struct Val {
ConflictResolution Resolution;
// Lanes written by this def, 0 for unanalyzed values.
unsigned WriteLanes;
// Lanes with defined values in this register. Other lanes are undef and
// safe to clobber.
unsigned ValidLanes;
// Value in LI being redefined by this def.
VNInfo *RedefVNI;
// Value in the other live range that overlaps this def, if any.
VNInfo *OtherVNI;
// Is this value an IMPLICIT_DEF that can be erased?
//
// IMPLICIT_DEF values should only exist at the end of a basic block that
// is a predecessor to a phi-value. These IMPLICIT_DEF instructions can be
// safely erased if they are overlapping a live value in the other live
// interval.
//
// Weird control flow graphs and incomplete PHI handling in
// ProcessImplicitDefs can very rarely create IMPLICIT_DEF values with
// longer live ranges. Such IMPLICIT_DEF values should be treated like
// normal values.
bool ErasableImplicitDef;
// True when the live range of this value will be pruned because of an
// overlapping CR_Replace value in the other live range.
bool Pruned;
// True once Pruned above has been computed.
bool PrunedComputed;
Val() : Resolution(CR_Keep), WriteLanes(0), ValidLanes(0),
RedefVNI(0), OtherVNI(0), ErasableImplicitDef(false),
Pruned(false), PrunedComputed(false) {}
bool isAnalyzed() const { return WriteLanes != 0; }
};
// One entry per value number in LI.
SmallVector<Val, 8> Vals;
unsigned computeWriteLanes(const MachineInstr *DefMI, bool &Redef);
VNInfo *stripCopies(VNInfo *VNI);
ConflictResolution analyzeValue(unsigned ValNo, JoinVals &Other);
void computeAssignment(unsigned ValNo, JoinVals &Other);
bool taintExtent(unsigned, unsigned, JoinVals&,
SmallVectorImpl<std::pair<SlotIndex, unsigned> >&);
bool usesLanes(MachineInstr *MI, unsigned, unsigned, unsigned);
bool isPrunedValue(unsigned ValNo, JoinVals &Other);
public:
JoinVals(LiveInterval &li, unsigned subIdx,
SmallVectorImpl<VNInfo*> &newVNInfo,
const CoalescerPair &cp,
LiveIntervals *lis,
const TargetRegisterInfo *tri)
: LI(li), SubIdx(subIdx), NewVNInfo(newVNInfo), CP(cp), LIS(lis),
Indexes(LIS->getSlotIndexes()), TRI(tri),
Assignments(LI.getNumValNums(), -1), Vals(LI.getNumValNums())
{}
/// Analyze defs in LI and compute a value mapping in NewVNInfo.
/// Returns false if any conflicts were impossible to resolve.
bool mapValues(JoinVals &Other);
/// Try to resolve conflicts that require all values to be mapped.
/// Returns false if any conflicts were impossible to resolve.
bool resolveConflicts(JoinVals &Other);
/// Prune the live range of values in Other.LI where they would conflict with
/// CR_Replace values in LI. Collect end points for restoring the live range
/// after joining.
void pruneValues(JoinVals &Other, SmallVectorImpl<SlotIndex> &EndPoints);
/// Erase any machine instructions that have been coalesced away.
/// Add erased instructions to ErasedInstrs.
/// Add foreign virtual registers to ShrinkRegs if their live range ended at
/// the erased instrs.
void eraseInstrs(SmallPtrSet<MachineInstr*, 8> &ErasedInstrs,
SmallVectorImpl<unsigned> &ShrinkRegs);
/// Get the value assignments suitable for passing to LiveInterval::join.
const int *getAssignments() const { return Assignments.data(); }
};
} // end anonymous namespace
/// Compute the bitmask of lanes actually written by DefMI.
/// Set Redef if there are any partial register definitions that depend on the
/// previous value of the register.
unsigned JoinVals::computeWriteLanes(const MachineInstr *DefMI, bool &Redef) {
unsigned L = 0;
for (ConstMIOperands MO(DefMI); MO.isValid(); ++MO) {
if (!MO->isReg() || MO->getReg() != LI.reg || !MO->isDef())
continue;
L |= TRI->getSubRegIndexLaneMask(
TRI->composeSubRegIndices(SubIdx, MO->getSubReg()));
if (MO->readsReg())
Redef = true;
}
return L;
}
/// Find the ultimate value that VNI was copied from.
VNInfo *JoinVals::stripCopies(VNInfo *VNI) {
while (!VNI->isPHIDef()) {
MachineInstr *MI = Indexes->getInstructionFromIndex(VNI->def);
assert(MI && "No defining instruction");
if (!MI->isFullCopy())
break;
unsigned Reg = MI->getOperand(1).getReg();
if (!TargetRegisterInfo::isVirtualRegister(Reg))
break;
LiveRangeQuery LRQ(LIS->getInterval(Reg), VNI->def);
if (!LRQ.valueIn())
break;
VNI = LRQ.valueIn();
}
return VNI;
}
/// Analyze ValNo in this live range, and set all fields of Vals[ValNo].
/// Return a conflict resolution when possible, but leave the hard cases as
/// CR_Unresolved.
/// Recursively calls computeAssignment() on this and Other, guaranteeing that
/// both OtherVNI and RedefVNI have been analyzed and mapped before returning.
/// The recursion always goes upwards in the dominator tree, making loops
/// impossible.
JoinVals::ConflictResolution
JoinVals::analyzeValue(unsigned ValNo, JoinVals &Other) {
Val &V = Vals[ValNo];
assert(!V.isAnalyzed() && "Value has already been analyzed!");
VNInfo *VNI = LI.getValNumInfo(ValNo);
if (VNI->isUnused()) {
V.WriteLanes = ~0u;
return CR_Keep;
}
// Get the instruction defining this value, compute the lanes written.
const MachineInstr *DefMI = 0;
if (VNI->isPHIDef()) {
// Conservatively assume that all lanes in a PHI are valid.
V.ValidLanes = V.WriteLanes = TRI->getSubRegIndexLaneMask(SubIdx);
} else {
DefMI = Indexes->getInstructionFromIndex(VNI->def);
bool Redef = false;
V.ValidLanes = V.WriteLanes = computeWriteLanes(DefMI, Redef);
// If this is a read-modify-write instruction, there may be more valid
// lanes than the ones written by this instruction.
// This only covers partial redef operands. DefMI may have normal use
// operands reading the register. They don't contribute valid lanes.
//
// This adds ssub1 to the set of valid lanes in %src:
//
// %src:ssub1<def> = FOO
//
// This leaves only ssub1 valid, making any other lanes undef:
//
// %src:ssub1<def,read-undef> = FOO %src:ssub2
//
// The <read-undef> flag on the def operand means that old lane values are
// not important.
if (Redef) {
V.RedefVNI = LiveRangeQuery(LI, VNI->def).valueIn();
assert(V.RedefVNI && "Instruction is reading nonexistent value");
computeAssignment(V.RedefVNI->id, Other);
V.ValidLanes |= Vals[V.RedefVNI->id].ValidLanes;
}
// An IMPLICIT_DEF writes undef values.
if (DefMI->isImplicitDef()) {
// We normally expect IMPLICIT_DEF values to be live only until the end
// of their block. If the value is really live longer and gets pruned in
// another block, this flag is cleared again.
V.ErasableImplicitDef = true;
V.ValidLanes &= ~V.WriteLanes;
}
}
// Find the value in Other that overlaps VNI->def, if any.
LiveRangeQuery OtherLRQ(Other.LI, VNI->def);
// It is possible that both values are defined by the same instruction, or
// the values are PHIs defined in the same block. When that happens, the two
// values should be merged into one, but not into any preceding value.
// The first value defined or visited gets CR_Keep, the other gets CR_Merge.
if (VNInfo *OtherVNI = OtherLRQ.valueDefined()) {
assert(SlotIndex::isSameInstr(VNI->def, OtherVNI->def) && "Broken LRQ");
// One value stays, the other is merged. Keep the earlier one, or the first
// one we see.
if (OtherVNI->def < VNI->def)
Other.computeAssignment(OtherVNI->id, *this);
else if (VNI->def < OtherVNI->def && OtherLRQ.valueIn()) {
// This is an early-clobber def overlapping a live-in value in the other
// register. Not mergeable.
V.OtherVNI = OtherLRQ.valueIn();
return CR_Impossible;
}
V.OtherVNI = OtherVNI;
Val &OtherV = Other.Vals[OtherVNI->id];
// Keep this value, check for conflicts when analyzing OtherVNI.
if (!OtherV.isAnalyzed())
return CR_Keep;
// Both sides have been analyzed now.
// Allow overlapping PHI values. Any real interference would show up in a
// predecessor, the PHI itself can't introduce any conflicts.
if (VNI->isPHIDef())
return CR_Merge;
if (V.ValidLanes & OtherV.ValidLanes)
// Overlapping lanes can't be resolved.
return CR_Impossible;
else
return CR_Merge;
}
// No simultaneous def. Is Other live at the def?
V.OtherVNI = OtherLRQ.valueIn();
if (!V.OtherVNI)
// No overlap, no conflict.
return CR_Keep;
assert(!SlotIndex::isSameInstr(VNI->def, V.OtherVNI->def) && "Broken LRQ");
// We have overlapping values, or possibly a kill of Other.
// Recursively compute assignments up the dominator tree.
Other.computeAssignment(V.OtherVNI->id, *this);
Val &OtherV = Other.Vals[V.OtherVNI->id];
// Check if OtherV is an IMPLICIT_DEF that extends beyond its basic block.
// This shouldn't normally happen, but ProcessImplicitDefs can leave such
// IMPLICIT_DEF instructions behind, and there is nothing wrong with it
// technically.
//
// WHen it happens, treat that IMPLICIT_DEF as a normal value, and don't try
// to erase the IMPLICIT_DEF instruction.
if (OtherV.ErasableImplicitDef && DefMI &&
DefMI->getParent() != Indexes->getMBBFromIndex(V.OtherVNI->def)) {
DEBUG(dbgs() << "IMPLICIT_DEF defined at " << V.OtherVNI->def
<< " extends into BB#" << DefMI->getParent()->getNumber()
<< ", keeping it.\n");
OtherV.ErasableImplicitDef = false;
}
// Allow overlapping PHI values. Any real interference would show up in a
// predecessor, the PHI itself can't introduce any conflicts.
if (VNI->isPHIDef())
return CR_Replace;
// Check for simple erasable conflicts.
if (DefMI->isImplicitDef())
return CR_Erase;
// Include the non-conflict where DefMI is a coalescable copy that kills
// OtherVNI. We still want the copy erased and value numbers merged.
if (CP.isCoalescable(DefMI)) {
// Some of the lanes copied from OtherVNI may be undef, making them undef
// here too.
V.ValidLanes &= ~V.WriteLanes | OtherV.ValidLanes;
return CR_Erase;
}
// This may not be a real conflict if DefMI simply kills Other and defines
// VNI.
if (OtherLRQ.isKill() && OtherLRQ.endPoint() <= VNI->def)
return CR_Keep;
// Handle the case where VNI and OtherVNI can be proven to be identical:
//
// %other = COPY %ext
// %this = COPY %ext <-- Erase this copy
//
if (DefMI->isFullCopy() && !CP.isPartial() &&
stripCopies(VNI) == stripCopies(V.OtherVNI))
return CR_Erase;
// If the lanes written by this instruction were all undef in OtherVNI, it is
// still safe to join the live ranges. This can't be done with a simple value
// mapping, though - OtherVNI will map to multiple values:
//
// 1 %dst:ssub0 = FOO <-- OtherVNI
// 2 %src = BAR <-- VNI
// 3 %dst:ssub1 = COPY %src<kill> <-- Eliminate this copy.
// 4 BAZ %dst<kill>
// 5 QUUX %src<kill>
//
// Here OtherVNI will map to itself in [1;2), but to VNI in [2;5). CR_Replace
// handles this complex value mapping.
if ((V.WriteLanes & OtherV.ValidLanes) == 0)
return CR_Replace;
// If the other live range is killed by DefMI and the live ranges are still
// overlapping, it must be because we're looking at an early clobber def:
//
// %dst<def,early-clobber> = ASM %src<kill>
//
// In this case, it is illegal to merge the two live ranges since the early
// clobber def would clobber %src before it was read.
if (OtherLRQ.isKill()) {
// This case where the def doesn't overlap the kill is handled above.
assert(VNI->def.isEarlyClobber() &&
"Only early clobber defs can overlap a kill");
return CR_Impossible;
}
// VNI is clobbering live lanes in OtherVNI, but there is still the
// possibility that no instructions actually read the clobbered lanes.
// If we're clobbering all the lanes in OtherVNI, at least one must be read.
// Otherwise Other.LI wouldn't be live here.
if ((TRI->getSubRegIndexLaneMask(Other.SubIdx) & ~V.WriteLanes) == 0)
return CR_Impossible;
// We need to verify that no instructions are reading the clobbered lanes. To
// save compile time, we'll only check that locally. Don't allow the tainted
// value to escape the basic block.
MachineBasicBlock *MBB = Indexes->getMBBFromIndex(VNI->def);
if (OtherLRQ.endPoint() >= Indexes->getMBBEndIdx(MBB))
return CR_Impossible;
// There are still some things that could go wrong besides clobbered lanes
// being read, for example OtherVNI may be only partially redefined in MBB,
// and some clobbered lanes could escape the block. Save this analysis for
// resolveConflicts() when all values have been mapped. We need to know
// RedefVNI and WriteLanes for any later defs in MBB, and we can't compute
// that now - the recursive analyzeValue() calls must go upwards in the
// dominator tree.
return CR_Unresolved;
}
/// Compute the value assignment for ValNo in LI.
/// This may be called recursively by analyzeValue(), but never for a ValNo on
/// the stack.
void JoinVals::computeAssignment(unsigned ValNo, JoinVals &Other) {
Val &V = Vals[ValNo];
if (V.isAnalyzed()) {
// Recursion should always move up the dominator tree, so ValNo is not
// supposed to reappear before it has been assigned.
assert(Assignments[ValNo] != -1 && "Bad recursion?");
return;
}
switch ((V.Resolution = analyzeValue(ValNo, Other))) {
case CR_Erase:
case CR_Merge:
// Merge this ValNo into OtherVNI.
assert(V.OtherVNI && "OtherVNI not assigned, can't merge.");
assert(Other.Vals[V.OtherVNI->id].isAnalyzed() && "Missing recursion");
Assignments[ValNo] = Other.Assignments[V.OtherVNI->id];
DEBUG(dbgs() << "\t\tmerge " << PrintReg(LI.reg) << ':' << ValNo << '@'
<< LI.getValNumInfo(ValNo)->def << " into "
<< PrintReg(Other.LI.reg) << ':' << V.OtherVNI->id << '@'
<< V.OtherVNI->def << " --> @"
<< NewVNInfo[Assignments[ValNo]]->def << '\n');
break;
case CR_Replace:
case CR_Unresolved:
// The other value is going to be pruned if this join is successful.
assert(V.OtherVNI && "OtherVNI not assigned, can't prune");
Other.Vals[V.OtherVNI->id].Pruned = true;
// Fall through.
default:
// This value number needs to go in the final joined live range.
Assignments[ValNo] = NewVNInfo.size();
NewVNInfo.push_back(LI.getValNumInfo(ValNo));
break;
}
}
bool JoinVals::mapValues(JoinVals &Other) {
for (unsigned i = 0, e = LI.getNumValNums(); i != e; ++i) {
computeAssignment(i, Other);
if (Vals[i].Resolution == CR_Impossible) {
DEBUG(dbgs() << "\t\tinterference at " << PrintReg(LI.reg) << ':' << i
<< '@' << LI.getValNumInfo(i)->def << '\n');
return false;
}
}
return true;
}
/// Assuming ValNo is going to clobber some valid lanes in Other.LI, compute
/// the extent of the tainted lanes in the block.
///
/// Multiple values in Other.LI can be affected since partial redefinitions can
/// preserve previously tainted lanes.
///
/// 1 %dst = VLOAD <-- Define all lanes in %dst
/// 2 %src = FOO <-- ValNo to be joined with %dst:ssub0
/// 3 %dst:ssub1 = BAR <-- Partial redef doesn't clear taint in ssub0
/// 4 %dst:ssub0 = COPY %src <-- Conflict resolved, ssub0 wasn't read
///
/// For each ValNo in Other that is affected, add an (EndIndex, TaintedLanes)
/// entry to TaintedVals.
///
/// Returns false if the tainted lanes extend beyond the basic block.
bool JoinVals::
taintExtent(unsigned ValNo, unsigned TaintedLanes, JoinVals &Other,
SmallVectorImpl<std::pair<SlotIndex, unsigned> > &TaintExtent) {
VNInfo *VNI = LI.getValNumInfo(ValNo);
MachineBasicBlock *MBB = Indexes->getMBBFromIndex(VNI->def);
SlotIndex MBBEnd = Indexes->getMBBEndIdx(MBB);
// Scan Other.LI from VNI.def to MBBEnd.
LiveInterval::iterator OtherI = Other.LI.find(VNI->def);
assert(OtherI != Other.LI.end() && "No conflict?");
do {
// OtherI is pointing to a tainted value. Abort the join if the tainted
// lanes escape the block.
SlotIndex End = OtherI->end;
if (End >= MBBEnd) {
DEBUG(dbgs() << "\t\ttaints global " << PrintReg(Other.LI.reg) << ':'
<< OtherI->valno->id << '@' << OtherI->start << '\n');
return false;
}
DEBUG(dbgs() << "\t\ttaints local " << PrintReg(Other.LI.reg) << ':'
<< OtherI->valno->id << '@' << OtherI->start
<< " to " << End << '\n');
// A dead def is not a problem.
if (End.isDead())
break;
TaintExtent.push_back(std::make_pair(End, TaintedLanes));
// Check for another def in the MBB.
if (++OtherI == Other.LI.end() || OtherI->start >= MBBEnd)
break;
// Lanes written by the new def are no longer tainted.
const Val &OV = Other.Vals[OtherI->valno->id];
TaintedLanes &= ~OV.WriteLanes;
if (!OV.RedefVNI)
break;
} while (TaintedLanes);
return true;
}
/// Return true if MI uses any of the given Lanes from Reg.
/// This does not include partial redefinitions of Reg.
bool JoinVals::usesLanes(MachineInstr *MI, unsigned Reg, unsigned SubIdx,
unsigned Lanes) {
if (MI->isDebugValue())
return false;
for (ConstMIOperands MO(MI); MO.isValid(); ++MO) {
if (!MO->isReg() || MO->isDef() || MO->getReg() != Reg)
continue;
if (!MO->readsReg())
continue;
if (Lanes & TRI->getSubRegIndexLaneMask(
TRI->composeSubRegIndices(SubIdx, MO->getSubReg())))
return true;
}
return false;
}
bool JoinVals::resolveConflicts(JoinVals &Other) {
for (unsigned i = 0, e = LI.getNumValNums(); i != e; ++i) {
Val &V = Vals[i];
assert (V.Resolution != CR_Impossible && "Unresolvable conflict");
if (V.Resolution != CR_Unresolved)
continue;
DEBUG(dbgs() << "\t\tconflict at " << PrintReg(LI.reg) << ':' << i
<< '@' << LI.getValNumInfo(i)->def << '\n');
++NumLaneConflicts;
assert(V.OtherVNI && "Inconsistent conflict resolution.");
VNInfo *VNI = LI.getValNumInfo(i);
const Val &OtherV = Other.Vals[V.OtherVNI->id];
// VNI is known to clobber some lanes in OtherVNI. If we go ahead with the
// join, those lanes will be tainted with a wrong value. Get the extent of
// the tainted lanes.
unsigned TaintedLanes = V.WriteLanes & OtherV.ValidLanes;
SmallVector<std::pair<SlotIndex, unsigned>, 8> TaintExtent;
if (!taintExtent(i, TaintedLanes, Other, TaintExtent))
// Tainted lanes would extend beyond the basic block.
return false;
assert(!TaintExtent.empty() && "There should be at least one conflict.");
// Now look at the instructions from VNI->def to TaintExtent (inclusive).
MachineBasicBlock *MBB = Indexes->getMBBFromIndex(VNI->def);
MachineBasicBlock::iterator MI = MBB->begin();
if (!VNI->isPHIDef()) {
MI = Indexes->getInstructionFromIndex(VNI->def);
// No need to check the instruction defining VNI for reads.
++MI;
}
assert(!SlotIndex::isSameInstr(VNI->def, TaintExtent.front().first) &&
"Interference ends on VNI->def. Should have been handled earlier");
MachineInstr *LastMI =
Indexes->getInstructionFromIndex(TaintExtent.front().first);
assert(LastMI && "Range must end at a proper instruction");
unsigned TaintNum = 0;
for(;;) {
assert(MI != MBB->end() && "Bad LastMI");
if (usesLanes(MI, Other.LI.reg, Other.SubIdx, TaintedLanes)) {
DEBUG(dbgs() << "\t\ttainted lanes used by: " << *MI);
return false;
}
// LastMI is the last instruction to use the current value.
if (&*MI == LastMI) {
if (++TaintNum == TaintExtent.size())
break;
LastMI = Indexes->getInstructionFromIndex(TaintExtent[TaintNum].first);
assert(LastMI && "Range must end at a proper instruction");
TaintedLanes = TaintExtent[TaintNum].second;
}
++MI;
}
// The tainted lanes are unused.
V.Resolution = CR_Replace;
++NumLaneResolves;
}
return true;
}
// Determine if ValNo is a copy of a value number in LI or Other.LI that will
// be pruned:
//
// %dst = COPY %src
// %src = COPY %dst <-- This value to be pruned.
// %dst = COPY %src <-- This value is a copy of a pruned value.
//
bool JoinVals::isPrunedValue(unsigned ValNo, JoinVals &Other) {
Val &V = Vals[ValNo];
if (V.Pruned || V.PrunedComputed)
return V.Pruned;
if (V.Resolution != CR_Erase && V.Resolution != CR_Merge)
return V.Pruned;
// Follow copies up the dominator tree and check if any intermediate value
// has been pruned.
V.PrunedComputed = true;
V.Pruned = Other.isPrunedValue(V.OtherVNI->id, *this);
return V.Pruned;
}
void JoinVals::pruneValues(JoinVals &Other,
SmallVectorImpl<SlotIndex> &EndPoints) {
for (unsigned i = 0, e = LI.getNumValNums(); i != e; ++i) {
SlotIndex Def = LI.getValNumInfo(i)->def;
switch (Vals[i].Resolution) {
case CR_Keep:
break;
case CR_Replace: {
// This value takes precedence over the value in Other.LI.
LIS->pruneValue(&Other.LI, Def, &EndPoints);
// Check if we're replacing an IMPLICIT_DEF value. The IMPLICIT_DEF
// instructions are only inserted to provide a live-out value for PHI
// predecessors, so the instruction should simply go away once its value
// has been replaced.
Val &OtherV = Other.Vals[Vals[i].OtherVNI->id];
bool EraseImpDef = OtherV.ErasableImplicitDef &&
OtherV.Resolution == CR_Keep;
if (!Def.isBlock()) {
// Remove <def,read-undef> flags. This def is now a partial redef.
// Also remove <def,dead> flags since the joined live range will
// continue past this instruction.
for (MIOperands MO(Indexes->getInstructionFromIndex(Def));
MO.isValid(); ++MO)
if (MO->isReg() && MO->isDef() && MO->getReg() == LI.reg) {
MO->setIsUndef(EraseImpDef);
MO->setIsDead(false);
}
// This value will reach instructions below, but we need to make sure
// the live range also reaches the instruction at Def.
if (!EraseImpDef)
EndPoints.push_back(Def);
}
DEBUG(dbgs() << "\t\tpruned " << PrintReg(Other.LI.reg) << " at " << Def
<< ": " << Other.LI << '\n');
break;
}
case CR_Erase:
case CR_Merge:
if (isPrunedValue(i, Other)) {
// This value is ultimately a copy of a pruned value in LI or Other.LI.
// We can no longer trust the value mapping computed by
// computeAssignment(), the value that was originally copied could have
// been replaced.
LIS->pruneValue(&LI, Def, &EndPoints);
DEBUG(dbgs() << "\t\tpruned all of " << PrintReg(LI.reg) << " at "
<< Def << ": " << LI << '\n');
}
break;
case CR_Unresolved:
case CR_Impossible:
llvm_unreachable("Unresolved conflicts");
}
}
}
void JoinVals::eraseInstrs(SmallPtrSet<MachineInstr*, 8> &ErasedInstrs,
SmallVectorImpl<unsigned> &ShrinkRegs) {
for (unsigned i = 0, e = LI.getNumValNums(); i != e; ++i) {
// Get the def location before markUnused() below invalidates it.
SlotIndex Def = LI.getValNumInfo(i)->def;
switch (Vals[i].Resolution) {
case CR_Keep:
// If an IMPLICIT_DEF value is pruned, it doesn't serve a purpose any
// longer. The IMPLICIT_DEF instructions are only inserted by
// PHIElimination to guarantee that all PHI predecessors have a value.
if (!Vals[i].ErasableImplicitDef || !Vals[i].Pruned)
break;
// Remove value number i from LI. Note that this VNInfo is still present
// in NewVNInfo, so it will appear as an unused value number in the final
// joined interval.
LI.getValNumInfo(i)->markUnused();
LI.removeValNo(LI.getValNumInfo(i));
DEBUG(dbgs() << "\t\tremoved " << i << '@' << Def << ": " << LI << '\n');
// FALL THROUGH.
case CR_Erase: {
MachineInstr *MI = Indexes->getInstructionFromIndex(Def);
assert(MI && "No instruction to erase");
if (MI->isCopy()) {
unsigned Reg = MI->getOperand(1).getReg();
if (TargetRegisterInfo::isVirtualRegister(Reg) &&
Reg != CP.getSrcReg() && Reg != CP.getDstReg())
ShrinkRegs.push_back(Reg);
}
ErasedInstrs.insert(MI);
DEBUG(dbgs() << "\t\terased:\t" << Def << '\t' << *MI);
LIS->RemoveMachineInstrFromMaps(MI);
MI->eraseFromParent();
break;
}
default:
break;
}
}
}
bool RegisterCoalescer::joinVirtRegs(CoalescerPair &CP) {
SmallVector<VNInfo*, 16> NewVNInfo;
LiveInterval &RHS = LIS->getInterval(CP.getSrcReg());
LiveInterval &LHS = LIS->getInterval(CP.getDstReg());
JoinVals RHSVals(RHS, CP.getSrcIdx(), NewVNInfo, CP, LIS, TRI);
JoinVals LHSVals(LHS, CP.getDstIdx(), NewVNInfo, CP, LIS, TRI);
DEBUG(dbgs() << "\t\tRHS = " << PrintReg(CP.getSrcReg()) << ' ' << RHS
<< "\n\t\tLHS = " << PrintReg(CP.getDstReg()) << ' ' << LHS
<< '\n');
// First compute NewVNInfo and the simple value mappings.
// Detect impossible conflicts early.
if (!LHSVals.mapValues(RHSVals) || !RHSVals.mapValues(LHSVals))
return false;
// Some conflicts can only be resolved after all values have been mapped.
if (!LHSVals.resolveConflicts(RHSVals) || !RHSVals.resolveConflicts(LHSVals))
return false;
// All clear, the live ranges can be merged.
// The merging algorithm in LiveInterval::join() can't handle conflicting
// value mappings, so we need to remove any live ranges that overlap a
// CR_Replace resolution. Collect a set of end points that can be used to
// restore the live range after joining.
SmallVector<SlotIndex, 8> EndPoints;
LHSVals.pruneValues(RHSVals, EndPoints);
RHSVals.pruneValues(LHSVals, EndPoints);
// Erase COPY and IMPLICIT_DEF instructions. This may cause some external
// registers to require trimming.
SmallVector<unsigned, 8> ShrinkRegs;
LHSVals.eraseInstrs(ErasedInstrs, ShrinkRegs);
RHSVals.eraseInstrs(ErasedInstrs, ShrinkRegs);
while (!ShrinkRegs.empty())
LIS->shrinkToUses(&LIS->getInterval(ShrinkRegs.pop_back_val()));
// Join RHS into LHS.
LHS.join(RHS, LHSVals.getAssignments(), RHSVals.getAssignments(), NewVNInfo,
MRI);
// Kill flags are going to be wrong if the live ranges were overlapping.
// Eventually, we should simply clear all kill flags when computing live
// ranges. They are reinserted after register allocation.
MRI->clearKillFlags(LHS.reg);
MRI->clearKillFlags(RHS.reg);
if (EndPoints.empty())
return true;
// Recompute the parts of the live range we had to remove because of
// CR_Replace conflicts.
DEBUG(dbgs() << "\t\trestoring liveness to " << EndPoints.size()
<< " points: " << LHS << '\n');
LIS->extendToIndices(&LHS, EndPoints);
return true;
}
/// joinIntervals - Attempt to join these two intervals. On failure, this
/// returns false.
bool RegisterCoalescer::joinIntervals(CoalescerPair &CP) {
return CP.isPhys() ? joinReservedPhysReg(CP) : joinVirtRegs(CP);
}
namespace {
// Information concerning MBB coalescing priority.
struct MBBPriorityInfo {
MachineBasicBlock *MBB;
unsigned Depth;
bool IsSplit;
MBBPriorityInfo(MachineBasicBlock *mbb, unsigned depth, bool issplit)
: MBB(mbb), Depth(depth), IsSplit(issplit) {}
};
}
// C-style comparator that sorts first based on the loop depth of the basic
// block (the unsigned), and then on the MBB number.
//
// EnableGlobalCopies assumes that the primary sort key is loop depth.
static int compareMBBPriority(const void *L, const void *R) {
const MBBPriorityInfo *LHS = static_cast<const MBBPriorityInfo*>(L);
const MBBPriorityInfo *RHS = static_cast<const MBBPriorityInfo*>(R);
// Deeper loops first
if (LHS->Depth != RHS->Depth)
return LHS->Depth > RHS->Depth ? -1 : 1;
// Try to unsplit critical edges next.
if (LHS->IsSplit != RHS->IsSplit)
return LHS->IsSplit ? -1 : 1;
// Prefer blocks that are more connected in the CFG. This takes care of
// the most difficult copies first while intervals are short.
unsigned cl = LHS->MBB->pred_size() + LHS->MBB->succ_size();
unsigned cr = RHS->MBB->pred_size() + RHS->MBB->succ_size();
if (cl != cr)
return cl > cr ? -1 : 1;
// As a last resort, sort by block number.
return LHS->MBB->getNumber() < RHS->MBB->getNumber() ? -1 : 1;
}
/// \returns true if the given copy uses or defines a local live range.
static bool isLocalCopy(MachineInstr *Copy, const LiveIntervals *LIS) {
if (!Copy->isCopy())
return false;
if (Copy->getOperand(1).isUndef())
return false;
unsigned SrcReg = Copy->getOperand(1).getReg();
unsigned DstReg = Copy->getOperand(0).getReg();
if (TargetRegisterInfo::isPhysicalRegister(SrcReg)
|| TargetRegisterInfo::isPhysicalRegister(DstReg))
return false;
return LIS->intervalIsInOneMBB(LIS->getInterval(SrcReg))
|| LIS->intervalIsInOneMBB(LIS->getInterval(DstReg));
}
// Try joining WorkList copies starting from index From.
// Null out any successful joins.
bool RegisterCoalescer::
copyCoalesceWorkList(MutableArrayRef<MachineInstr*> CurrList) {
bool Progress = false;
for (unsigned i = 0, e = CurrList.size(); i != e; ++i) {
if (!CurrList[i])
continue;
// Skip instruction pointers that have already been erased, for example by
// dead code elimination.
if (ErasedInstrs.erase(CurrList[i])) {
CurrList[i] = 0;
continue;
}
bool Again = false;
bool Success = joinCopy(CurrList[i], Again);
Progress |= Success;
if (Success || !Again)
CurrList[i] = 0;
}
return Progress;
}
void
RegisterCoalescer::copyCoalesceInMBB(MachineBasicBlock *MBB) {
DEBUG(dbgs() << MBB->getName() << ":\n");
// Collect all copy-like instructions in MBB. Don't start coalescing anything
// yet, it might invalidate the iterator.
const unsigned PrevSize = WorkList.size();
if (JoinGlobalCopies) {
// Coalesce copies bottom-up to coalesce local defs before local uses. They
// are not inherently easier to resolve, but slightly preferable until we
// have local live range splitting. In particular this is required by
// cmp+jmp macro fusion.
for (MachineBasicBlock::iterator MII = MBB->begin(), E = MBB->end();
MII != E; ++MII) {
if (!MII->isCopyLike())
continue;
if (isLocalCopy(&(*MII), LIS))
LocalWorkList.push_back(&(*MII));
else
WorkList.push_back(&(*MII));
}
}
else {
for (MachineBasicBlock::iterator MII = MBB->begin(), E = MBB->end();
MII != E; ++MII)
if (MII->isCopyLike())
WorkList.push_back(MII);
}
// Try coalescing the collected copies immediately, and remove the nulls.
// This prevents the WorkList from getting too large since most copies are
// joinable on the first attempt.
MutableArrayRef<MachineInstr*>
CurrList(WorkList.begin() + PrevSize, WorkList.end());
if (copyCoalesceWorkList(CurrList))
WorkList.erase(std::remove(WorkList.begin() + PrevSize, WorkList.end(),
(MachineInstr*)0), WorkList.end());
}
void RegisterCoalescer::coalesceLocals() {
copyCoalesceWorkList(LocalWorkList);
for (unsigned j = 0, je = LocalWorkList.size(); j != je; ++j) {
if (LocalWorkList[j])
WorkList.push_back(LocalWorkList[j]);
}
LocalWorkList.clear();
}
void RegisterCoalescer::joinAllIntervals() {
DEBUG(dbgs() << "********** JOINING INTERVALS ***********\n");
assert(WorkList.empty() && LocalWorkList.empty() && "Old data still around.");
std::vector<MBBPriorityInfo> MBBs;
MBBs.reserve(MF->size());
for (MachineFunction::iterator I = MF->begin(), E = MF->end();I != E;++I){
MachineBasicBlock *MBB = I;
MBBs.push_back(MBBPriorityInfo(MBB, Loops->getLoopDepth(MBB),
JoinSplitEdges && isSplitEdge(MBB)));
}
array_pod_sort(MBBs.begin(), MBBs.end(), compareMBBPriority);
// Coalesce intervals in MBB priority order.
unsigned CurrDepth = UINT_MAX;
for (unsigned i = 0, e = MBBs.size(); i != e; ++i) {
// Try coalescing the collected local copies for deeper loops.
if (JoinGlobalCopies && MBBs[i].Depth < CurrDepth) {
coalesceLocals();
CurrDepth = MBBs[i].Depth;
}
copyCoalesceInMBB(MBBs[i].MBB);
}
coalesceLocals();
// Joining intervals can allow other intervals to be joined. Iteratively join
// until we make no progress.
while (copyCoalesceWorkList(WorkList))
/* empty */ ;
}
void RegisterCoalescer::releaseMemory() {
ErasedInstrs.clear();
WorkList.clear();
DeadDefs.clear();
InflateRegs.clear();
}
bool RegisterCoalescer::runOnMachineFunction(MachineFunction &fn) {
MF = &fn;
MRI = &fn.getRegInfo();
TM = &fn.getTarget();
TRI = TM->getRegisterInfo();
TII = TM->getInstrInfo();
LIS = &getAnalysis<LiveIntervals>();
AA = &getAnalysis<AliasAnalysis>();
Loops = &getAnalysis<MachineLoopInfo>();
const TargetSubtargetInfo &ST = TM->getSubtarget<TargetSubtargetInfo>();
if (EnableGlobalCopies == cl::BOU_UNSET)
JoinGlobalCopies = ST.enableMachineScheduler();
else
JoinGlobalCopies = (EnableGlobalCopies == cl::BOU_TRUE);
// The MachineScheduler does not currently require JoinSplitEdges. This will
// either be enabled unconditionally or replaced by a more general live range
// splitting optimization.
JoinSplitEdges = EnableJoinSplits;
DEBUG(dbgs() << "********** SIMPLE REGISTER COALESCING **********\n"
<< "********** Function: " << MF->getName() << '\n');
if (VerifyCoalescing)
MF->verify(this, "Before register coalescing");
RegClassInfo.runOnMachineFunction(fn);
// Join (coalesce) intervals if requested.
if (EnableJoining)
joinAllIntervals();
// After deleting a lot of copies, register classes may be less constrained.
// Removing sub-register operands may allow GR32_ABCD -> GR32 and DPR_VFP2 ->
// DPR inflation.
array_pod_sort(InflateRegs.begin(), InflateRegs.end());
InflateRegs.erase(std::unique(InflateRegs.begin(), InflateRegs.end()),
InflateRegs.end());
DEBUG(dbgs() << "Trying to inflate " << InflateRegs.size() << " regs.\n");
for (unsigned i = 0, e = InflateRegs.size(); i != e; ++i) {
unsigned Reg = InflateRegs[i];
if (MRI->reg_nodbg_empty(Reg))
continue;
if (MRI->recomputeRegClass(Reg, *TM)) {
DEBUG(dbgs() << PrintReg(Reg) << " inflated to "
<< MRI->getRegClass(Reg)->getName() << '\n');
++NumInflated;
}
}
DEBUG(dump());
if (VerifyCoalescing)
MF->verify(this, "After register coalescing");
return true;
}
/// print - Implement the dump method.
void RegisterCoalescer::print(raw_ostream &O, const Module* m) const {
LIS->print(O, m);
}