/*
* Copyright (C) 2016 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#include "loop_optimization.h"
#include "arch/instruction_set.h"
#include "arch/arm/instruction_set_features_arm.h"
#include "arch/arm64/instruction_set_features_arm64.h"
#include "arch/mips/instruction_set_features_mips.h"
#include "arch/mips64/instruction_set_features_mips64.h"
#include "arch/x86/instruction_set_features_x86.h"
#include "arch/x86_64/instruction_set_features_x86_64.h"
#include "driver/compiler_driver.h"
#include "linear_order.h"
namespace art {
// Enables vectorization (SIMDization) in the loop optimizer.
static constexpr bool kEnableVectorization = true;
// Remove the instruction from the graph. A bit more elaborate than the usual
// instruction removal, since there may be a cycle in the use structure.
static void RemoveFromCycle(HInstruction* instruction) {
instruction->RemoveAsUserOfAllInputs();
instruction->RemoveEnvironmentUsers();
instruction->GetBlock()->RemoveInstructionOrPhi(instruction, /*ensure_safety=*/ false);
}
// Detect a goto block and sets succ to the single successor.
static bool IsGotoBlock(HBasicBlock* block, /*out*/ HBasicBlock** succ) {
if (block->GetPredecessors().size() == 1 &&
block->GetSuccessors().size() == 1 &&
block->IsSingleGoto()) {
*succ = block->GetSingleSuccessor();
return true;
}
return false;
}
// Detect an early exit loop.
static bool IsEarlyExit(HLoopInformation* loop_info) {
HBlocksInLoopReversePostOrderIterator it_loop(*loop_info);
for (it_loop.Advance(); !it_loop.Done(); it_loop.Advance()) {
for (HBasicBlock* successor : it_loop.Current()->GetSuccessors()) {
if (!loop_info->Contains(*successor)) {
return true;
}
}
}
return false;
}
// Detect a sign extension from the given type. Returns the promoted operand on success.
static bool IsSignExtensionAndGet(HInstruction* instruction,
Primitive::Type type,
/*out*/ HInstruction** operand) {
// Accept any already wider constant that would be handled properly by sign
// extension when represented in the *width* of the given narrower data type
// (the fact that char normally zero extends does not matter here).
int64_t value = 0;
if (IsInt64AndGet(instruction, &value)) {
switch (type) {
case Primitive::kPrimByte:
if (std::numeric_limits<int8_t>::min() <= value &&
std::numeric_limits<int8_t>::max() >= value) {
*operand = instruction;
return true;
}
return false;
case Primitive::kPrimChar:
case Primitive::kPrimShort:
if (std::numeric_limits<int16_t>::min() <= value &&
std::numeric_limits<int16_t>::max() <= value) {
*operand = instruction;
return true;
}
return false;
default:
return false;
}
}
// An implicit widening conversion of a signed integer to an integral type sign-extends
// the two's-complement representation of the integer value to fill the wider format.
if (instruction->GetType() == type && (instruction->IsArrayGet() ||
instruction->IsStaticFieldGet() ||
instruction->IsInstanceFieldGet())) {
switch (type) {
case Primitive::kPrimByte:
case Primitive::kPrimShort:
*operand = instruction;
return true;
default:
return false;
}
}
// TODO: perhaps explicit conversions later too?
// (this may return something different from instruction)
return false;
}
// Detect a zero extension from the given type. Returns the promoted operand on success.
static bool IsZeroExtensionAndGet(HInstruction* instruction,
Primitive::Type type,
/*out*/ HInstruction** operand) {
// Accept any already wider constant that would be handled properly by zero
// extension when represented in the *width* of the given narrower data type
// (the fact that byte/short normally sign extend does not matter here).
int64_t value = 0;
if (IsInt64AndGet(instruction, &value)) {
switch (type) {
case Primitive::kPrimByte:
if (std::numeric_limits<uint8_t>::min() <= value &&
std::numeric_limits<uint8_t>::max() >= value) {
*operand = instruction;
return true;
}
return false;
case Primitive::kPrimChar:
case Primitive::kPrimShort:
if (std::numeric_limits<uint16_t>::min() <= value &&
std::numeric_limits<uint16_t>::max() <= value) {
*operand = instruction;
return true;
}
return false;
default:
return false;
}
}
// An implicit widening conversion of a char to an integral type zero-extends
// the representation of the char value to fill the wider format.
if (instruction->GetType() == type && (instruction->IsArrayGet() ||
instruction->IsStaticFieldGet() ||
instruction->IsInstanceFieldGet())) {
if (type == Primitive::kPrimChar) {
*operand = instruction;
return true;
}
}
// A sign (or zero) extension followed by an explicit removal of just the
// higher sign bits is equivalent to a zero extension of the underlying operand.
if (instruction->IsAnd()) {
int64_t mask = 0;
HInstruction* a = instruction->InputAt(0);
HInstruction* b = instruction->InputAt(1);
// In (a & b) find (mask & b) or (a & mask) with sign or zero extension on the non-mask.
if ((IsInt64AndGet(a, /*out*/ &mask) && (IsSignExtensionAndGet(b, type, /*out*/ operand) ||
IsZeroExtensionAndGet(b, type, /*out*/ operand))) ||
(IsInt64AndGet(b, /*out*/ &mask) && (IsSignExtensionAndGet(a, type, /*out*/ operand) ||
IsZeroExtensionAndGet(a, type, /*out*/ operand)))) {
switch ((*operand)->GetType()) {
case Primitive::kPrimByte: return mask == std::numeric_limits<uint8_t>::max();
case Primitive::kPrimChar:
case Primitive::kPrimShort: return mask == std::numeric_limits<uint16_t>::max();
default: return false;
}
}
}
// TODO: perhaps explicit conversions later too?
return false;
}
// Test vector restrictions.
static bool HasVectorRestrictions(uint64_t restrictions, uint64_t tested) {
return (restrictions & tested) != 0;
}
// Insert an instruction.
static HInstruction* Insert(HBasicBlock* block, HInstruction* instruction) {
DCHECK(block != nullptr);
DCHECK(instruction != nullptr);
block->InsertInstructionBefore(instruction, block->GetLastInstruction());
return instruction;
}
//
// Class methods.
//
HLoopOptimization::HLoopOptimization(HGraph* graph,
CompilerDriver* compiler_driver,
HInductionVarAnalysis* induction_analysis)
: HOptimization(graph, kLoopOptimizationPassName),
compiler_driver_(compiler_driver),
induction_range_(induction_analysis),
loop_allocator_(nullptr),
global_allocator_(graph_->GetArena()),
top_loop_(nullptr),
last_loop_(nullptr),
iset_(nullptr),
induction_simplication_count_(0),
simplified_(false),
vector_length_(0),
vector_refs_(nullptr),
vector_map_(nullptr) {
}
void HLoopOptimization::Run() {
// Skip if there is no loop or the graph has try-catch/irreducible loops.
// TODO: make this less of a sledgehammer.
if (!graph_->HasLoops() || graph_->HasTryCatch() || graph_->HasIrreducibleLoops()) {
return;
}
// Phase-local allocator that draws from the global pool. Since the allocator
// itself resides on the stack, it is destructed on exiting Run(), which
// implies its underlying memory is released immediately.
ArenaAllocator allocator(global_allocator_->GetArenaPool());
loop_allocator_ = &allocator;
// Perform loop optimizations.
LocalRun();
if (top_loop_ == nullptr) {
graph_->SetHasLoops(false); // no more loops
}
// Detach.
loop_allocator_ = nullptr;
last_loop_ = top_loop_ = nullptr;
}
void HLoopOptimization::LocalRun() {
// Build the linear order using the phase-local allocator. This step enables building
// a loop hierarchy that properly reflects the outer-inner and previous-next relation.
ArenaVector<HBasicBlock*> linear_order(loop_allocator_->Adapter(kArenaAllocLinearOrder));
LinearizeGraph(graph_, loop_allocator_, &linear_order);
// Build the loop hierarchy.
for (HBasicBlock* block : linear_order) {
if (block->IsLoopHeader()) {
AddLoop(block->GetLoopInformation());
}
}
// Traverse the loop hierarchy inner-to-outer and optimize. Traversal can use
// temporary data structures using the phase-local allocator. All new HIR
// should use the global allocator.
if (top_loop_ != nullptr) {
ArenaSet<HInstruction*> iset(loop_allocator_->Adapter(kArenaAllocLoopOptimization));
ArenaSet<ArrayReference> refs(loop_allocator_->Adapter(kArenaAllocLoopOptimization));
ArenaSafeMap<HInstruction*, HInstruction*> map(
std::less<HInstruction*>(), loop_allocator_->Adapter(kArenaAllocLoopOptimization));
// Attach.
iset_ = &iset;
vector_refs_ = &refs;
vector_map_ = ↦
// Traverse.
TraverseLoopsInnerToOuter(top_loop_);
// Detach.
iset_ = nullptr;
vector_refs_ = nullptr;
vector_map_ = nullptr;
}
}
void HLoopOptimization::AddLoop(HLoopInformation* loop_info) {
DCHECK(loop_info != nullptr);
LoopNode* node = new (loop_allocator_) LoopNode(loop_info);
if (last_loop_ == nullptr) {
// First loop.
DCHECK(top_loop_ == nullptr);
last_loop_ = top_loop_ = node;
} else if (loop_info->IsIn(*last_loop_->loop_info)) {
// Inner loop.
node->outer = last_loop_;
DCHECK(last_loop_->inner == nullptr);
last_loop_ = last_loop_->inner = node;
} else {
// Subsequent loop.
while (last_loop_->outer != nullptr && !loop_info->IsIn(*last_loop_->outer->loop_info)) {
last_loop_ = last_loop_->outer;
}
node->outer = last_loop_->outer;
node->previous = last_loop_;
DCHECK(last_loop_->next == nullptr);
last_loop_ = last_loop_->next = node;
}
}
void HLoopOptimization::RemoveLoop(LoopNode* node) {
DCHECK(node != nullptr);
DCHECK(node->inner == nullptr);
if (node->previous != nullptr) {
// Within sequence.
node->previous->next = node->next;
if (node->next != nullptr) {
node->next->previous = node->previous;
}
} else {
// First of sequence.
if (node->outer != nullptr) {
node->outer->inner = node->next;
} else {
top_loop_ = node->next;
}
if (node->next != nullptr) {
node->next->outer = node->outer;
node->next->previous = nullptr;
}
}
}
void HLoopOptimization::TraverseLoopsInnerToOuter(LoopNode* node) {
for ( ; node != nullptr; node = node->next) {
// Visit inner loops first.
uint32_t current_induction_simplification_count = induction_simplication_count_;
if (node->inner != nullptr) {
TraverseLoopsInnerToOuter(node->inner);
}
// Recompute induction information of this loop if the induction
// of any inner loop has been simplified.
if (current_induction_simplification_count != induction_simplication_count_) {
induction_range_.ReVisit(node->loop_info);
}
// Repeat simplifications in the loop-body until no more changes occur.
// Note that since each simplification consists of eliminating code (without
// introducing new code), this process is always finite.
do {
simplified_ = false;
SimplifyInduction(node);
SimplifyBlocks(node);
} while (simplified_);
// Optimize inner loop.
if (node->inner == nullptr) {
OptimizeInnerLoop(node);
}
}
}
//
// Optimization.
//
bool HLoopOptimization::CanRemoveCycle() {
for (HInstruction* i : *iset_) {
// We can never remove instructions that have environment
// uses when we compile 'debuggable'.
if (i->HasEnvironmentUses() && graph_->IsDebuggable()) {
return false;
}
// A deoptimization should never have an environment input removed.
for (const HUseListNode<HEnvironment*>& use : i->GetEnvUses()) {
if (use.GetUser()->GetHolder()->IsDeoptimize()) {
return false;
}
}
}
return true;
}
void HLoopOptimization::SimplifyInduction(LoopNode* node) {
HBasicBlock* header = node->loop_info->GetHeader();
HBasicBlock* preheader = node->loop_info->GetPreHeader();
// Scan the phis in the header to find opportunities to simplify an induction
// cycle that is only used outside the loop. Replace these uses, if any, with
// the last value and remove the induction cycle.
// Examples: for (int i = 0; x != null; i++) { .... no i .... }
// for (int i = 0; i < 10; i++, k++) { .... no k .... } return k;
for (HInstructionIterator it(header->GetPhis()); !it.Done(); it.Advance()) {
HPhi* phi = it.Current()->AsPhi();
iset_->clear(); // prepare phi induction
if (TrySetPhiInduction(phi, /*restrict_uses*/ true) &&
TryAssignLastValue(node->loop_info, phi, preheader, /*collect_loop_uses*/ false)) {
// Note that it's ok to have replaced uses after the loop with the last value, without
// being able to remove the cycle. Environment uses (which are the reason we may not be
// able to remove the cycle) within the loop will still hold the right value.
if (CanRemoveCycle()) {
for (HInstruction* i : *iset_) {
RemoveFromCycle(i);
}
simplified_ = true;
}
}
}
}
void HLoopOptimization::SimplifyBlocks(LoopNode* node) {
// Iterate over all basic blocks in the loop-body.
for (HBlocksInLoopIterator it(*node->loop_info); !it.Done(); it.Advance()) {
HBasicBlock* block = it.Current();
// Remove dead instructions from the loop-body.
RemoveDeadInstructions(block->GetPhis());
RemoveDeadInstructions(block->GetInstructions());
// Remove trivial control flow blocks from the loop-body.
if (block->GetPredecessors().size() == 1 &&
block->GetSuccessors().size() == 1 &&
block->GetSingleSuccessor()->GetPredecessors().size() == 1) {
simplified_ = true;
block->MergeWith(block->GetSingleSuccessor());
} else if (block->GetSuccessors().size() == 2) {
// Trivial if block can be bypassed to either branch.
HBasicBlock* succ0 = block->GetSuccessors()[0];
HBasicBlock* succ1 = block->GetSuccessors()[1];
HBasicBlock* meet0 = nullptr;
HBasicBlock* meet1 = nullptr;
if (succ0 != succ1 &&
IsGotoBlock(succ0, &meet0) &&
IsGotoBlock(succ1, &meet1) &&
meet0 == meet1 && // meets again
meet0 != block && // no self-loop
meet0->GetPhis().IsEmpty()) { // not used for merging
simplified_ = true;
succ0->DisconnectAndDelete();
if (block->Dominates(meet0)) {
block->RemoveDominatedBlock(meet0);
succ1->AddDominatedBlock(meet0);
meet0->SetDominator(succ1);
}
}
}
}
}
void HLoopOptimization::OptimizeInnerLoop(LoopNode* node) {
HBasicBlock* header = node->loop_info->GetHeader();
HBasicBlock* preheader = node->loop_info->GetPreHeader();
// Ensure loop header logic is finite.
int64_t trip_count = 0;
if (!induction_range_.IsFinite(node->loop_info, &trip_count)) {
return;
}
// Ensure there is only a single loop-body (besides the header).
HBasicBlock* body = nullptr;
for (HBlocksInLoopIterator it(*node->loop_info); !it.Done(); it.Advance()) {
if (it.Current() != header) {
if (body != nullptr) {
return;
}
body = it.Current();
}
}
// Ensure there is only a single exit point.
if (header->GetSuccessors().size() != 2) {
return;
}
HBasicBlock* exit = (header->GetSuccessors()[0] == body)
? header->GetSuccessors()[1]
: header->GetSuccessors()[0];
// Ensure exit can only be reached by exiting loop.
if (exit->GetPredecessors().size() != 1) {
return;
}
// Detect either an empty loop (no side effects other than plain iteration) or
// a trivial loop (just iterating once). Replace subsequent index uses, if any,
// with the last value and remove the loop, possibly after unrolling its body.
HInstruction* phi = header->GetFirstPhi();
iset_->clear(); // prepare phi induction
if (TrySetSimpleLoopHeader(header)) {
bool is_empty = IsEmptyBody(body);
if ((is_empty || trip_count == 1) &&
TryAssignLastValue(node->loop_info, phi, preheader, /*collect_loop_uses*/ true)) {
if (!is_empty) {
// Unroll the loop-body, which sees initial value of the index.
phi->ReplaceWith(phi->InputAt(0));
preheader->MergeInstructionsWith(body);
}
body->DisconnectAndDelete();
exit->RemovePredecessor(header);
header->RemoveSuccessor(exit);
header->RemoveDominatedBlock(exit);
header->DisconnectAndDelete();
preheader->AddSuccessor(exit);
preheader->AddInstruction(new (global_allocator_) HGoto());
preheader->AddDominatedBlock(exit);
exit->SetDominator(preheader);
RemoveLoop(node); // update hierarchy
return;
}
}
// Vectorize loop, if possible and valid.
if (kEnableVectorization) {
iset_->clear(); // prepare phi induction
if (TrySetSimpleLoopHeader(header) &&
CanVectorize(node, body, trip_count) &&
TryAssignLastValue(node->loop_info, phi, preheader, /*collect_loop_uses*/ true)) {
Vectorize(node, body, exit, trip_count);
graph_->SetHasSIMD(true); // flag SIMD usage
return;
}
}
}
//
// Loop vectorization. The implementation is based on the book by Aart J.C. Bik:
// "The Software Vectorization Handbook. Applying Multimedia Extensions for Maximum Performance."
// Intel Press, June, 2004 (http://www.aartbik.com/).
//
bool HLoopOptimization::CanVectorize(LoopNode* node, HBasicBlock* block, int64_t trip_count) {
// Reset vector bookkeeping.
vector_length_ = 0;
vector_refs_->clear();
vector_runtime_test_a_ =
vector_runtime_test_b_= nullptr;
// Phis in the loop-body prevent vectorization.
if (!block->GetPhis().IsEmpty()) {
return false;
}
// Scan the loop-body, starting a right-hand-side tree traversal at each left-hand-side
// occurrence, which allows passing down attributes down the use tree.
for (HInstructionIterator it(block->GetInstructions()); !it.Done(); it.Advance()) {
if (!VectorizeDef(node, it.Current(), /*generate_code*/ false)) {
return false; // failure to vectorize a left-hand-side
}
}
// Heuristics. Does vectorization seem profitable?
// TODO: refine
if (vector_length_ == 0) {
return false; // nothing found
} else if (0 < trip_count && trip_count < vector_length_) {
return false; // insufficient iterations
}
// Data dependence analysis. Find each pair of references with same type, where
// at least one is a write. Each such pair denotes a possible data dependence.
// This analysis exploits the property that differently typed arrays cannot be
// aliased, as well as the property that references either point to the same
// array or to two completely disjoint arrays, i.e., no partial aliasing.
// Other than a few simply heuristics, no detailed subscript analysis is done.
for (auto i = vector_refs_->begin(); i != vector_refs_->end(); ++i) {
for (auto j = i; ++j != vector_refs_->end(); ) {
if (i->type == j->type && (i->lhs || j->lhs)) {
// Found same-typed a[i+x] vs. b[i+y], where at least one is a write.
HInstruction* a = i->base;
HInstruction* b = j->base;
HInstruction* x = i->offset;
HInstruction* y = j->offset;
if (a == b) {
// Found a[i+x] vs. a[i+y]. Accept if x == y (loop-independent data dependence).
// Conservatively assume a loop-carried data dependence otherwise, and reject.
if (x != y) {
return false;
}
} else {
// Found a[i+x] vs. b[i+y]. Accept if x == y (at worst loop-independent data dependence).
// Conservatively assume a potential loop-carried data dependence otherwise, avoided by
// generating an explicit a != b disambiguation runtime test on the two references.
if (x != y) {
// For now, we reject after one test to avoid excessive overhead.
if (vector_runtime_test_a_ != nullptr) {
return false;
}
vector_runtime_test_a_ = a;
vector_runtime_test_b_ = b;
}
}
}
}
}
// Success!
return true;
}
void HLoopOptimization::Vectorize(LoopNode* node,
HBasicBlock* block,
HBasicBlock* exit,
int64_t trip_count) {
Primitive::Type induc_type = Primitive::kPrimInt;
HBasicBlock* header = node->loop_info->GetHeader();
HBasicBlock* preheader = node->loop_info->GetPreHeader();
// A cleanup is needed for any unknown trip count or for a known trip count
// with remainder iterations after vectorization.
bool needs_cleanup = trip_count == 0 || (trip_count % vector_length_) != 0;
// Adjust vector bookkeeping.
iset_->clear(); // prepare phi induction
bool is_simple_loop_header = TrySetSimpleLoopHeader(header); // fills iset_
DCHECK(is_simple_loop_header);
// Generate preheader:
// stc = <trip-count>;
// vtc = stc - stc % VL;
HInstruction* stc = induction_range_.GenerateTripCount(node->loop_info, graph_, preheader);
HInstruction* vtc = stc;
if (needs_cleanup) {
DCHECK(IsPowerOfTwo(vector_length_));
HInstruction* rem = Insert(
preheader, new (global_allocator_) HAnd(induc_type,
stc,
graph_->GetIntConstant(vector_length_ - 1)));
vtc = Insert(preheader, new (global_allocator_) HSub(induc_type, stc, rem));
}
// Generate runtime disambiguation test:
// vtc = a != b ? vtc : 0;
if (vector_runtime_test_a_ != nullptr) {
HInstruction* rt = Insert(
preheader,
new (global_allocator_) HNotEqual(vector_runtime_test_a_, vector_runtime_test_b_));
vtc = Insert(preheader,
new (global_allocator_) HSelect(rt, vtc, graph_->GetIntConstant(0), kNoDexPc));
needs_cleanup = true;
}
// Generate vector loop:
// for (i = 0; i < vtc; i += VL)
// <vectorized-loop-body>
vector_mode_ = kVector;
GenerateNewLoop(node,
block,
graph_->TransformLoopForVectorization(header, block, exit),
graph_->GetIntConstant(0),
vtc,
graph_->GetIntConstant(vector_length_));
HLoopInformation* vloop = vector_header_->GetLoopInformation();
// Generate cleanup loop, if needed:
// for ( ; i < stc; i += 1)
// <loop-body>
if (needs_cleanup) {
vector_mode_ = kSequential;
GenerateNewLoop(node,
block,
graph_->TransformLoopForVectorization(vector_header_, vector_body_, exit),
vector_phi_,
stc,
graph_->GetIntConstant(1));
}
// Remove the original loop by disconnecting the body block
// and removing all instructions from the header.
block->DisconnectAndDelete();
while (!header->GetFirstInstruction()->IsGoto()) {
header->RemoveInstruction(header->GetFirstInstruction());
}
// Update loop hierarchy: the old header now resides in the
// same outer loop as the old preheader.
header->SetLoopInformation(preheader->GetLoopInformation()); // outward
node->loop_info = vloop;
}
void HLoopOptimization::GenerateNewLoop(LoopNode* node,
HBasicBlock* block,
HBasicBlock* new_preheader,
HInstruction* lo,
HInstruction* hi,
HInstruction* step) {
Primitive::Type induc_type = Primitive::kPrimInt;
// Prepare new loop.
vector_map_->clear();
vector_preheader_ = new_preheader,
vector_header_ = vector_preheader_->GetSingleSuccessor();
vector_body_ = vector_header_->GetSuccessors()[1];
vector_phi_ = new (global_allocator_) HPhi(global_allocator_,
kNoRegNumber,
0,
HPhi::ToPhiType(induc_type));
// Generate header and prepare body.
// for (i = lo; i < hi; i += step)
// <loop-body>
HInstruction* cond = new (global_allocator_) HAboveOrEqual(vector_phi_, hi);
vector_header_->AddPhi(vector_phi_);
vector_header_->AddInstruction(cond);
vector_header_->AddInstruction(new (global_allocator_) HIf(cond));
for (HInstructionIterator it(block->GetInstructions()); !it.Done(); it.Advance()) {
bool vectorized_def = VectorizeDef(node, it.Current(), /*generate_code*/ true);
DCHECK(vectorized_def);
}
// Generate body from the instruction map, but in original program order.
HEnvironment* env = vector_header_->GetFirstInstruction()->GetEnvironment();
for (HInstructionIterator it(block->GetInstructions()); !it.Done(); it.Advance()) {
auto i = vector_map_->find(it.Current());
if (i != vector_map_->end() && !i->second->IsInBlock()) {
Insert(vector_body_, i->second);
// Deal with instructions that need an environment, such as the scalar intrinsics.
if (i->second->NeedsEnvironment()) {
i->second->CopyEnvironmentFromWithLoopPhiAdjustment(env, vector_header_);
}
}
}
// Finalize increment and phi.
HInstruction* inc = new (global_allocator_) HAdd(induc_type, vector_phi_, step);
vector_phi_->AddInput(lo);
vector_phi_->AddInput(Insert(vector_body_, inc));
}
// TODO: accept reductions at left-hand-side, mixed-type store idioms, etc.
bool HLoopOptimization::VectorizeDef(LoopNode* node,
HInstruction* instruction,
bool generate_code) {
// Accept a left-hand-side array base[index] for
// (1) supported vector type,
// (2) loop-invariant base,
// (3) unit stride index,
// (4) vectorizable right-hand-side value.
uint64_t restrictions = kNone;
if (instruction->IsArraySet()) {
Primitive::Type type = instruction->AsArraySet()->GetComponentType();
HInstruction* base = instruction->InputAt(0);
HInstruction* index = instruction->InputAt(1);
HInstruction* value = instruction->InputAt(2);
HInstruction* offset = nullptr;
if (TrySetVectorType(type, &restrictions) &&
node->loop_info->IsDefinedOutOfTheLoop(base) &&
induction_range_.IsUnitStride(instruction, index, &offset) &&
VectorizeUse(node, value, generate_code, type, restrictions)) {
if (generate_code) {
GenerateVecSub(index, offset);
GenerateVecMem(instruction, vector_map_->Get(index), vector_map_->Get(value), type);
} else {
vector_refs_->insert(ArrayReference(base, offset, type, /*lhs*/ true));
}
return true;
}
return false;
}
// Branch back okay.
if (instruction->IsGoto()) {
return true;
}
// Otherwise accept only expressions with no effects outside the immediate loop-body.
// Note that actual uses are inspected during right-hand-side tree traversal.
return !IsUsedOutsideLoop(node->loop_info, instruction) && !instruction->DoesAnyWrite();
}
// TODO: more operations and intrinsics, detect saturation arithmetic, etc.
bool HLoopOptimization::VectorizeUse(LoopNode* node,
HInstruction* instruction,
bool generate_code,
Primitive::Type type,
uint64_t restrictions) {
// Accept anything for which code has already been generated.
if (generate_code) {
if (vector_map_->find(instruction) != vector_map_->end()) {
return true;
}
}
// Continue the right-hand-side tree traversal, passing in proper
// types and vector restrictions along the way. During code generation,
// all new nodes are drawn from the global allocator.
if (node->loop_info->IsDefinedOutOfTheLoop(instruction)) {
// Accept invariant use, using scalar expansion.
if (generate_code) {
GenerateVecInv(instruction, type);
}
return true;
} else if (instruction->IsArrayGet()) {
// Strings are different, with a different offset to the actual data
// and some compressed to save memory. For now, all cases are rejected
// to avoid the complexity.
if (instruction->AsArrayGet()->IsStringCharAt()) {
return false;
}
// Accept a right-hand-side array base[index] for
// (1) exact matching vector type,
// (2) loop-invariant base,
// (3) unit stride index,
// (4) vectorizable right-hand-side value.
HInstruction* base = instruction->InputAt(0);
HInstruction* index = instruction->InputAt(1);
HInstruction* offset = nullptr;
if (type == instruction->GetType() &&
node->loop_info->IsDefinedOutOfTheLoop(base) &&
induction_range_.IsUnitStride(instruction, index, &offset)) {
if (generate_code) {
GenerateVecSub(index, offset);
GenerateVecMem(instruction, vector_map_->Get(index), nullptr, type);
} else {
vector_refs_->insert(ArrayReference(base, offset, type, /*lhs*/ false));
}
return true;
}
} else if (instruction->IsTypeConversion()) {
// Accept particular type conversions.
HTypeConversion* conversion = instruction->AsTypeConversion();
HInstruction* opa = conversion->InputAt(0);
Primitive::Type from = conversion->GetInputType();
Primitive::Type to = conversion->GetResultType();
if ((to == Primitive::kPrimByte ||
to == Primitive::kPrimChar ||
to == Primitive::kPrimShort) && from == Primitive::kPrimInt) {
// Accept a "narrowing" type conversion from a "wider" computation for
// (1) conversion into final required type,
// (2) vectorizable operand,
// (3) "wider" operations cannot bring in higher order bits.
if (to == type && VectorizeUse(node, opa, generate_code, type, restrictions | kNoHiBits)) {
if (generate_code) {
if (vector_mode_ == kVector) {
vector_map_->Put(instruction, vector_map_->Get(opa)); // operand pass-through
} else {
GenerateVecOp(instruction, vector_map_->Get(opa), nullptr, type);
}
}
return true;
}
} else if (to == Primitive::kPrimFloat && from == Primitive::kPrimInt) {
DCHECK_EQ(to, type);
// Accept int to float conversion for
// (1) supported int,
// (2) vectorizable operand.
if (TrySetVectorType(from, &restrictions) &&
VectorizeUse(node, opa, generate_code, from, restrictions)) {
if (generate_code) {
GenerateVecOp(instruction, vector_map_->Get(opa), nullptr, type);
}
return true;
}
}
return false;
} else if (instruction->IsNeg() || instruction->IsNot() || instruction->IsBooleanNot()) {
// Accept unary operator for vectorizable operand.
HInstruction* opa = instruction->InputAt(0);
if (VectorizeUse(node, opa, generate_code, type, restrictions)) {
if (generate_code) {
GenerateVecOp(instruction, vector_map_->Get(opa), nullptr, type);
}
return true;
}
} else if (instruction->IsAdd() || instruction->IsSub() ||
instruction->IsMul() || instruction->IsDiv() ||
instruction->IsAnd() || instruction->IsOr() || instruction->IsXor()) {
// Deal with vector restrictions.
if ((instruction->IsMul() && HasVectorRestrictions(restrictions, kNoMul)) ||
(instruction->IsDiv() && HasVectorRestrictions(restrictions, kNoDiv))) {
return false;
}
// Accept binary operator for vectorizable operands.
HInstruction* opa = instruction->InputAt(0);
HInstruction* opb = instruction->InputAt(1);
if (VectorizeUse(node, opa, generate_code, type, restrictions) &&
VectorizeUse(node, opb, generate_code, type, restrictions)) {
if (generate_code) {
GenerateVecOp(instruction, vector_map_->Get(opa), vector_map_->Get(opb), type);
}
return true;
}
} else if (instruction->IsShl() || instruction->IsShr() || instruction->IsUShr()) {
// Recognize vectorization idioms.
if (VectorizeHalvingAddIdiom(node, instruction, generate_code, type, restrictions)) {
return true;
}
// Deal with vector restrictions.
if ((HasVectorRestrictions(restrictions, kNoShift)) ||
(instruction->IsShr() && HasVectorRestrictions(restrictions, kNoShr))) {
return false; // unsupported instruction
} else if ((instruction->IsShr() || instruction->IsUShr()) &&
HasVectorRestrictions(restrictions, kNoHiBits)) {
return false; // hibits may impact lobits; TODO: we can do better!
}
// Accept shift operator for vectorizable/invariant operands.
// TODO: accept symbolic, albeit loop invariant shift factors.
HInstruction* opa = instruction->InputAt(0);
HInstruction* opb = instruction->InputAt(1);
int64_t value = 0;
if (VectorizeUse(node, opa, generate_code, type, restrictions) && IsInt64AndGet(opb, &value)) {
// Make sure shift distance only looks at lower bits, as defined for sequential shifts.
int64_t mask = (instruction->GetType() == Primitive::kPrimLong)
? kMaxLongShiftDistance
: kMaxIntShiftDistance;
int64_t distance = value & mask;
// Restrict shift distance to packed data type width.
int64_t max_distance = Primitive::ComponentSize(type) * 8;
if (0 <= distance && distance < max_distance) {
if (generate_code) {
HInstruction* s = graph_->GetIntConstant(distance);
GenerateVecOp(instruction, vector_map_->Get(opa), s, type);
}
return true;
}
}
} else if (instruction->IsInvokeStaticOrDirect()) {
// Accept particular intrinsics.
HInvokeStaticOrDirect* invoke = instruction->AsInvokeStaticOrDirect();
switch (invoke->GetIntrinsic()) {
case Intrinsics::kMathAbsInt:
case Intrinsics::kMathAbsLong:
case Intrinsics::kMathAbsFloat:
case Intrinsics::kMathAbsDouble: {
// Deal with vector restrictions.
if (HasVectorRestrictions(restrictions, kNoAbs) ||
HasVectorRestrictions(restrictions, kNoHiBits)) {
// TODO: we can do better for some hibits cases.
return false;
}
// Accept ABS(x) for vectorizable operand.
HInstruction* opa = instruction->InputAt(0);
if (VectorizeUse(node, opa, generate_code, type, restrictions)) {
if (generate_code) {
GenerateVecOp(instruction, vector_map_->Get(opa), nullptr, type);
}
return true;
}
return false;
}
default:
return false;
} // switch
}
return false;
}
bool HLoopOptimization::TrySetVectorType(Primitive::Type type, uint64_t* restrictions) {
const InstructionSetFeatures* features = compiler_driver_->GetInstructionSetFeatures();
switch (compiler_driver_->GetInstructionSet()) {
case kArm:
case kThumb2:
return false;
case kArm64:
// Allow vectorization for all ARM devices, because Android assumes that
// ARMv8 AArch64 always supports advanced SIMD.
switch (type) {
case Primitive::kPrimBoolean:
case Primitive::kPrimByte:
*restrictions |= kNoDiv | kNoAbs;
return TrySetVectorLength(16);
case Primitive::kPrimChar:
case Primitive::kPrimShort:
*restrictions |= kNoDiv | kNoAbs;
return TrySetVectorLength(8);
case Primitive::kPrimInt:
*restrictions |= kNoDiv;
return TrySetVectorLength(4);
case Primitive::kPrimLong:
*restrictions |= kNoDiv | kNoMul;
return TrySetVectorLength(2);
case Primitive::kPrimFloat:
return TrySetVectorLength(4);
case Primitive::kPrimDouble:
return TrySetVectorLength(2);
default:
return false;
}
case kX86:
case kX86_64:
// Allow vectorization for SSE4-enabled X86 devices only (128-bit vectors).
if (features->AsX86InstructionSetFeatures()->HasSSE4_1()) {
switch (type) {
case Primitive::kPrimBoolean:
case Primitive::kPrimByte:
*restrictions |= kNoMul | kNoDiv | kNoShift | kNoAbs | kNoSignedHAdd | kNoUnroundedHAdd;
return TrySetVectorLength(16);
case Primitive::kPrimChar:
case Primitive::kPrimShort:
*restrictions |= kNoDiv | kNoAbs | kNoSignedHAdd | kNoUnroundedHAdd;
return TrySetVectorLength(8);
case Primitive::kPrimInt:
*restrictions |= kNoDiv;
return TrySetVectorLength(4);
case Primitive::kPrimLong:
*restrictions |= kNoMul | kNoDiv | kNoShr | kNoAbs;
return TrySetVectorLength(2);
case Primitive::kPrimFloat:
return TrySetVectorLength(4);
case Primitive::kPrimDouble:
return TrySetVectorLength(2);
default:
break;
} // switch type
}
return false;
case kMips:
case kMips64:
// TODO: implement MIPS SIMD.
return false;
default:
return false;
} // switch instruction set
}
bool HLoopOptimization::TrySetVectorLength(uint32_t length) {
DCHECK(IsPowerOfTwo(length) && length >= 2u);
// First time set?
if (vector_length_ == 0) {
vector_length_ = length;
}
// Different types are acceptable within a loop-body, as long as all the corresponding vector
// lengths match exactly to obtain a uniform traversal through the vector iteration space
// (idiomatic exceptions to this rule can be handled by further unrolling sub-expressions).
return vector_length_ == length;
}
void HLoopOptimization::GenerateVecInv(HInstruction* org, Primitive::Type type) {
if (vector_map_->find(org) == vector_map_->end()) {
// In scalar code, just use a self pass-through for scalar invariants
// (viz. expression remains itself).
if (vector_mode_ == kSequential) {
vector_map_->Put(org, org);
return;
}
// In vector code, explicit scalar expansion is needed.
HInstruction* vector = new (global_allocator_) HVecReplicateScalar(
global_allocator_, org, type, vector_length_);
vector_map_->Put(org, Insert(vector_preheader_, vector));
}
}
void HLoopOptimization::GenerateVecSub(HInstruction* org, HInstruction* offset) {
if (vector_map_->find(org) == vector_map_->end()) {
HInstruction* subscript = vector_phi_;
if (offset != nullptr) {
subscript = new (global_allocator_) HAdd(Primitive::kPrimInt, subscript, offset);
if (org->IsPhi()) {
Insert(vector_body_, subscript); // lacks layout placeholder
}
}
vector_map_->Put(org, subscript);
}
}
void HLoopOptimization::GenerateVecMem(HInstruction* org,
HInstruction* opa,
HInstruction* opb,
Primitive::Type type) {
HInstruction* vector = nullptr;
if (vector_mode_ == kVector) {
// Vector store or load.
if (opb != nullptr) {
vector = new (global_allocator_) HVecStore(
global_allocator_, org->InputAt(0), opa, opb, type, vector_length_);
} else {
bool is_string_char_at = org->AsArrayGet()->IsStringCharAt();
vector = new (global_allocator_) HVecLoad(
global_allocator_, org->InputAt(0), opa, type, vector_length_, is_string_char_at);
}
} else {
// Scalar store or load.
DCHECK(vector_mode_ == kSequential);
if (opb != nullptr) {
vector = new (global_allocator_) HArraySet(org->InputAt(0), opa, opb, type, kNoDexPc);
} else {
bool is_string_char_at = org->AsArrayGet()->IsStringCharAt();
vector = new (global_allocator_) HArrayGet(
org->InputAt(0), opa, type, kNoDexPc, is_string_char_at);
}
}
vector_map_->Put(org, vector);
}
#define GENERATE_VEC(x, y) \
if (vector_mode_ == kVector) { \
vector = (x); \
} else { \
DCHECK(vector_mode_ == kSequential); \
vector = (y); \
} \
break;
void HLoopOptimization::GenerateVecOp(HInstruction* org,
HInstruction* opa,
HInstruction* opb,
Primitive::Type type) {
if (vector_mode_ == kSequential) {
// Scalar code follows implicit integral promotion.
if (type == Primitive::kPrimBoolean ||
type == Primitive::kPrimByte ||
type == Primitive::kPrimChar ||
type == Primitive::kPrimShort) {
type = Primitive::kPrimInt;
}
}
HInstruction* vector = nullptr;
switch (org->GetKind()) {
case HInstruction::kNeg:
DCHECK(opb == nullptr);
GENERATE_VEC(
new (global_allocator_) HVecNeg(global_allocator_, opa, type, vector_length_),
new (global_allocator_) HNeg(type, opa));
case HInstruction::kNot:
DCHECK(opb == nullptr);
GENERATE_VEC(
new (global_allocator_) HVecNot(global_allocator_, opa, type, vector_length_),
new (global_allocator_) HNot(type, opa));
case HInstruction::kBooleanNot:
DCHECK(opb == nullptr);
GENERATE_VEC(
new (global_allocator_) HVecNot(global_allocator_, opa, type, vector_length_),
new (global_allocator_) HBooleanNot(opa));
case HInstruction::kTypeConversion:
DCHECK(opb == nullptr);
GENERATE_VEC(
new (global_allocator_) HVecCnv(global_allocator_, opa, type, vector_length_),
new (global_allocator_) HTypeConversion(type, opa, kNoDexPc));
case HInstruction::kAdd:
GENERATE_VEC(
new (global_allocator_) HVecAdd(global_allocator_, opa, opb, type, vector_length_),
new (global_allocator_) HAdd(type, opa, opb));
case HInstruction::kSub:
GENERATE_VEC(
new (global_allocator_) HVecSub(global_allocator_, opa, opb, type, vector_length_),
new (global_allocator_) HSub(type, opa, opb));
case HInstruction::kMul:
GENERATE_VEC(
new (global_allocator_) HVecMul(global_allocator_, opa, opb, type, vector_length_),
new (global_allocator_) HMul(type, opa, opb));
case HInstruction::kDiv:
GENERATE_VEC(
new (global_allocator_) HVecDiv(global_allocator_, opa, opb, type, vector_length_),
new (global_allocator_) HDiv(type, opa, opb, kNoDexPc));
case HInstruction::kAnd:
GENERATE_VEC(
new (global_allocator_) HVecAnd(global_allocator_, opa, opb, type, vector_length_),
new (global_allocator_) HAnd(type, opa, opb));
case HInstruction::kOr:
GENERATE_VEC(
new (global_allocator_) HVecOr(global_allocator_, opa, opb, type, vector_length_),
new (global_allocator_) HOr(type, opa, opb));
case HInstruction::kXor:
GENERATE_VEC(
new (global_allocator_) HVecXor(global_allocator_, opa, opb, type, vector_length_),
new (global_allocator_) HXor(type, opa, opb));
case HInstruction::kShl:
GENERATE_VEC(
new (global_allocator_) HVecShl(global_allocator_, opa, opb, type, vector_length_),
new (global_allocator_) HShl(type, opa, opb));
case HInstruction::kShr:
GENERATE_VEC(
new (global_allocator_) HVecShr(global_allocator_, opa, opb, type, vector_length_),
new (global_allocator_) HShr(type, opa, opb));
case HInstruction::kUShr:
GENERATE_VEC(
new (global_allocator_) HVecUShr(global_allocator_, opa, opb, type, vector_length_),
new (global_allocator_) HUShr(type, opa, opb));
case HInstruction::kInvokeStaticOrDirect: {
HInvokeStaticOrDirect* invoke = org->AsInvokeStaticOrDirect();
if (vector_mode_ == kVector) {
switch (invoke->GetIntrinsic()) {
case Intrinsics::kMathAbsInt:
case Intrinsics::kMathAbsLong:
case Intrinsics::kMathAbsFloat:
case Intrinsics::kMathAbsDouble:
DCHECK(opb == nullptr);
vector = new (global_allocator_) HVecAbs(global_allocator_, opa, type, vector_length_);
break;
default:
LOG(FATAL) << "Unsupported SIMD intrinsic";
UNREACHABLE();
} // switch invoke
} else {
// In scalar code, simply clone the method invoke, and replace its operands with the
// corresponding new scalar instructions in the loop. The instruction will get an
// environment while being inserted from the instruction map in original program order.
DCHECK(vector_mode_ == kSequential);
HInvokeStaticOrDirect* new_invoke = new (global_allocator_) HInvokeStaticOrDirect(
global_allocator_,
invoke->GetNumberOfArguments(),
invoke->GetType(),
invoke->GetDexPc(),
invoke->GetDexMethodIndex(),
invoke->GetResolvedMethod(),
invoke->GetDispatchInfo(),
invoke->GetInvokeType(),
invoke->GetTargetMethod(),
invoke->GetClinitCheckRequirement());
HInputsRef inputs = invoke->GetInputs();
for (size_t index = 0; index < inputs.size(); ++index) {
new_invoke->SetArgumentAt(index, vector_map_->Get(inputs[index]));
}
new_invoke->SetIntrinsic(invoke->GetIntrinsic(),
kNeedsEnvironmentOrCache,
kNoSideEffects,
kNoThrow);
vector = new_invoke;
}
break;
}
default:
break;
} // switch
CHECK(vector != nullptr) << "Unsupported SIMD operator";
vector_map_->Put(org, vector);
}
#undef GENERATE_VEC
//
// Vectorization idioms.
//
// Method recognizes the following idioms:
// rounding halving add (a + b + 1) >> 1 for unsigned/signed operands a, b
// regular halving add (a + b) >> 1 for unsigned/signed operands a, b
// Provided that the operands are promoted to a wider form to do the arithmetic and
// then cast back to narrower form, the idioms can be mapped into efficient SIMD
// implementation that operates directly in narrower form (plus one extra bit).
// TODO: current version recognizes implicit byte/short/char widening only;
// explicit widening from int to long could be added later.
bool HLoopOptimization::VectorizeHalvingAddIdiom(LoopNode* node,
HInstruction* instruction,
bool generate_code,
Primitive::Type type,
uint64_t restrictions) {
// Test for top level arithmetic shift right x >> 1 or logical shift right x >>> 1
// (note whether the sign bit in higher precision is shifted in has no effect
// on the narrow precision computed by the idiom).
int64_t value = 0;
if ((instruction->IsShr() ||
instruction->IsUShr()) &&
IsInt64AndGet(instruction->InputAt(1), &value) && value == 1) {
//
// TODO: make following code less sensitive to associativity and commutativity differences.
//
HInstruction* x = instruction->InputAt(0);
// Test for an optional rounding part (x + 1) >> 1.
bool is_rounded = false;
if (x->IsAdd() && IsInt64AndGet(x->InputAt(1), &value) && value == 1) {
x = x->InputAt(0);
is_rounded = true;
}
// Test for a core addition (a + b) >> 1 (possibly rounded), either unsigned or signed.
if (x->IsAdd()) {
HInstruction* a = x->InputAt(0);
HInstruction* b = x->InputAt(1);
HInstruction* r = nullptr;
HInstruction* s = nullptr;
bool is_unsigned = false;
if (IsZeroExtensionAndGet(a, type, &r) && IsZeroExtensionAndGet(b, type, &s)) {
is_unsigned = true;
} else if (IsSignExtensionAndGet(a, type, &r) && IsSignExtensionAndGet(b, type, &s)) {
is_unsigned = false;
} else {
return false;
}
// Deal with vector restrictions.
if ((!is_unsigned && HasVectorRestrictions(restrictions, kNoSignedHAdd)) ||
(!is_rounded && HasVectorRestrictions(restrictions, kNoUnroundedHAdd))) {
return false;
}
// Accept recognized halving add for vectorizable operands. Vectorized code uses the
// shorthand idiomatic operation. Sequential code uses the original scalar expressions.
DCHECK(r != nullptr && s != nullptr);
if (VectorizeUse(node, r, generate_code, type, restrictions) &&
VectorizeUse(node, s, generate_code, type, restrictions)) {
if (generate_code) {
if (vector_mode_ == kVector) {
vector_map_->Put(instruction, new (global_allocator_) HVecHalvingAdd(
global_allocator_,
vector_map_->Get(r),
vector_map_->Get(s),
type,
vector_length_,
is_unsigned,
is_rounded));
} else {
VectorizeUse(node, instruction->InputAt(0), generate_code, type, restrictions);
VectorizeUse(node, instruction->InputAt(1), generate_code, type, restrictions);
GenerateVecOp(instruction,
vector_map_->Get(instruction->InputAt(0)),
vector_map_->Get(instruction->InputAt(1)),
type);
}
}
return true;
}
}
}
return false;
}
//
// Helpers.
//
bool HLoopOptimization::TrySetPhiInduction(HPhi* phi, bool restrict_uses) {
DCHECK(iset_->empty());
ArenaSet<HInstruction*>* set = induction_range_.LookupCycle(phi);
if (set != nullptr) {
for (HInstruction* i : *set) {
// Check that, other than instructions that are no longer in the graph (removed earlier)
// each instruction is removable and, when restrict uses are requested, other than for phi,
// all uses are contained within the cycle.
if (!i->IsInBlock()) {
continue;
} else if (!i->IsRemovable()) {
return false;
} else if (i != phi && restrict_uses) {
for (const HUseListNode<HInstruction*>& use : i->GetUses()) {
if (set->find(use.GetUser()) == set->end()) {
return false;
}
}
}
iset_->insert(i); // copy
}
return true;
}
return false;
}
// Find: phi: Phi(init, addsub)
// s: SuspendCheck
// c: Condition(phi, bound)
// i: If(c)
// TODO: Find a less pattern matching approach?
bool HLoopOptimization::TrySetSimpleLoopHeader(HBasicBlock* block) {
DCHECK(iset_->empty());
HInstruction* phi = block->GetFirstPhi();
if (phi != nullptr &&
phi->GetNext() == nullptr &&
TrySetPhiInduction(phi->AsPhi(), /*restrict_uses*/ false)) {
HInstruction* s = block->GetFirstInstruction();
if (s != nullptr && s->IsSuspendCheck()) {
HInstruction* c = s->GetNext();
if (c != nullptr &&
c->IsCondition() &&
c->GetUses().HasExactlyOneElement() && // only used for termination
!c->HasEnvironmentUses()) { // unlikely, but not impossible
HInstruction* i = c->GetNext();
if (i != nullptr && i->IsIf() && i->InputAt(0) == c) {
iset_->insert(c);
iset_->insert(s);
return true;
}
}
}
}
return false;
}
bool HLoopOptimization::IsEmptyBody(HBasicBlock* block) {
if (!block->GetPhis().IsEmpty()) {
return false;
}
for (HInstructionIterator it(block->GetInstructions()); !it.Done(); it.Advance()) {
HInstruction* instruction = it.Current();
if (!instruction->IsGoto() && iset_->find(instruction) == iset_->end()) {
return false;
}
}
return true;
}
bool HLoopOptimization::IsUsedOutsideLoop(HLoopInformation* loop_info,
HInstruction* instruction) {
for (const HUseListNode<HInstruction*>& use : instruction->GetUses()) {
if (use.GetUser()->GetBlock()->GetLoopInformation() != loop_info) {
return true;
}
}
return false;
}
bool HLoopOptimization::IsOnlyUsedAfterLoop(HLoopInformation* loop_info,
HInstruction* instruction,
bool collect_loop_uses,
/*out*/ int32_t* use_count) {
for (const HUseListNode<HInstruction*>& use : instruction->GetUses()) {
HInstruction* user = use.GetUser();
if (iset_->find(user) == iset_->end()) { // not excluded?
HLoopInformation* other_loop_info = user->GetBlock()->GetLoopInformation();
if (other_loop_info != nullptr && other_loop_info->IsIn(*loop_info)) {
// If collect_loop_uses is set, simply keep adding those uses to the set.
// Otherwise, reject uses inside the loop that were not already in the set.
if (collect_loop_uses) {
iset_->insert(user);
continue;
}
return false;
}
++*use_count;
}
}
return true;
}
bool HLoopOptimization::TryReplaceWithLastValue(HLoopInformation* loop_info,
HInstruction* instruction,
HBasicBlock* block) {
// Try to replace outside uses with the last value.
if (induction_range_.CanGenerateLastValue(instruction)) {
HInstruction* replacement = induction_range_.GenerateLastValue(instruction, graph_, block);
const HUseList<HInstruction*>& uses = instruction->GetUses();
for (auto it = uses.begin(), end = uses.end(); it != end;) {
HInstruction* user = it->GetUser();
size_t index = it->GetIndex();
++it; // increment before replacing
if (iset_->find(user) == iset_->end()) { // not excluded?
if (kIsDebugBuild) {
// We have checked earlier in 'IsOnlyUsedAfterLoop' that the use is after the loop.
HLoopInformation* other_loop_info = user->GetBlock()->GetLoopInformation();
CHECK(other_loop_info == nullptr || !other_loop_info->IsIn(*loop_info));
}
user->ReplaceInput(replacement, index);
induction_range_.Replace(user, instruction, replacement); // update induction
}
}
const HUseList<HEnvironment*>& env_uses = instruction->GetEnvUses();
for (auto it = env_uses.begin(), end = env_uses.end(); it != end;) {
HEnvironment* user = it->GetUser();
size_t index = it->GetIndex();
++it; // increment before replacing
if (iset_->find(user->GetHolder()) == iset_->end()) { // not excluded?
HLoopInformation* other_loop_info = user->GetHolder()->GetBlock()->GetLoopInformation();
// Only update environment uses after the loop.
if (other_loop_info == nullptr || !other_loop_info->IsIn(*loop_info)) {
user->RemoveAsUserOfInput(index);
user->SetRawEnvAt(index, replacement);
replacement->AddEnvUseAt(user, index);
}
}
}
induction_simplication_count_++;
return true;
}
return false;
}
bool HLoopOptimization::TryAssignLastValue(HLoopInformation* loop_info,
HInstruction* instruction,
HBasicBlock* block,
bool collect_loop_uses) {
// Assigning the last value is always successful if there are no uses.
// Otherwise, it succeeds in a no early-exit loop by generating the
// proper last value assignment.
int32_t use_count = 0;
return IsOnlyUsedAfterLoop(loop_info, instruction, collect_loop_uses, &use_count) &&
(use_count == 0 ||
(!IsEarlyExit(loop_info) && TryReplaceWithLastValue(loop_info, instruction, block)));
}
void HLoopOptimization::RemoveDeadInstructions(const HInstructionList& list) {
for (HBackwardInstructionIterator i(list); !i.Done(); i.Advance()) {
HInstruction* instruction = i.Current();
if (instruction->IsDeadAndRemovable()) {
simplified_ = true;
instruction->GetBlock()->RemoveInstructionOrPhi(instruction);
}
}
}
} // namespace art