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// Copyright 2013 the V8 project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "src/hydrogen-uint32-analysis.h"
namespace v8 {
namespace internal {
static bool IsUnsignedLoad(HLoadKeyed* instr) {
switch (instr->elements_kind()) {
case EXTERNAL_UINT8_ELEMENTS:
case EXTERNAL_UINT16_ELEMENTS:
case EXTERNAL_UINT32_ELEMENTS:
case EXTERNAL_UINT8_CLAMPED_ELEMENTS:
case UINT8_ELEMENTS:
case UINT16_ELEMENTS:
case UINT32_ELEMENTS:
case UINT8_CLAMPED_ELEMENTS:
return true;
default:
return false;
}
}
static bool IsUint32Operation(HValue* instr) {
return instr->IsShr() ||
(instr->IsLoadKeyed() && IsUnsignedLoad(HLoadKeyed::cast(instr))) ||
(instr->IsInteger32Constant() && instr->GetInteger32Constant() >= 0);
}
bool HUint32AnalysisPhase::IsSafeUint32Use(HValue* val, HValue* use) {
// Operations that operate on bits are safe.
if (use->IsBitwise() || use->IsShl() || use->IsSar() || use->IsShr()) {
return true;
} else if (use->IsSimulate()) {
// Deoptimization has special support for uint32.
return true;
} else if (use->IsChange()) {
// Conversions have special support for uint32.
// This DCHECK guards that the conversion in question is actually
// implemented. Do not extend the whitelist without adding
// support to LChunkBuilder::DoChange().
DCHECK(HChange::cast(use)->to().IsDouble() ||
HChange::cast(use)->to().IsSmi() ||
HChange::cast(use)->to().IsTagged());
return true;
} else if (use->IsStoreKeyed()) {
HStoreKeyed* store = HStoreKeyed::cast(use);
if (store->is_external()) {
// Storing a value into an external integer array is a bit level
// operation.
if (store->value() == val) {
// Clamping or a conversion to double should have beed inserted.
DCHECK(store->elements_kind() != EXTERNAL_UINT8_CLAMPED_ELEMENTS);
DCHECK(store->elements_kind() != EXTERNAL_FLOAT32_ELEMENTS);
DCHECK(store->elements_kind() != EXTERNAL_FLOAT64_ELEMENTS);
return true;
}
}
} else if (use->IsCompareNumericAndBranch()) {
HCompareNumericAndBranch* c = HCompareNumericAndBranch::cast(use);
return IsUint32Operation(c->left()) && IsUint32Operation(c->right());
}
return false;
}
// Iterate over all uses and verify that they are uint32 safe: either don't
// distinguish between int32 and uint32 due to their bitwise nature or
// have special support for uint32 values.
// Encountered phis are optimistically treated as safe uint32 uses,
// marked with kUint32 flag and collected in the phis_ list. A separate
// pass will be performed later by UnmarkUnsafePhis to clear kUint32 from
// phis that are not actually uint32-safe (it requires fix point iteration).
bool HUint32AnalysisPhase::Uint32UsesAreSafe(HValue* uint32val) {
bool collect_phi_uses = false;
for (HUseIterator it(uint32val->uses()); !it.Done(); it.Advance()) {
HValue* use = it.value();
if (use->IsPhi()) {
if (!use->CheckFlag(HInstruction::kUint32)) {
// There is a phi use of this value from a phi that is not yet
// collected in phis_ array. Separate pass is required.
collect_phi_uses = true;
}
// Optimistically treat phis as uint32 safe.
continue;
}
if (!IsSafeUint32Use(uint32val, use)) {
return false;
}
}
if (collect_phi_uses) {
for (HUseIterator it(uint32val->uses()); !it.Done(); it.Advance()) {
HValue* use = it.value();
// There is a phi use of this value from a phi that is not yet
// collected in phis_ array. Separate pass is required.
if (use->IsPhi() && !use->CheckFlag(HInstruction::kUint32)) {
use->SetFlag(HInstruction::kUint32);
phis_.Add(HPhi::cast(use), zone());
}
}
}
return true;
}
// Check if all operands to the given phi are marked with kUint32 flag.
bool HUint32AnalysisPhase::CheckPhiOperands(HPhi* phi) {
if (!phi->CheckFlag(HInstruction::kUint32)) {
// This phi is not uint32 safe. No need to check operands.
return false;
}
for (int j = 0; j < phi->OperandCount(); j++) {
HValue* operand = phi->OperandAt(j);
if (!operand->CheckFlag(HInstruction::kUint32)) {
// Lazily mark constants that fit into uint32 range with kUint32 flag.
if (operand->IsInteger32Constant() &&
operand->GetInteger32Constant() >= 0) {
operand->SetFlag(HInstruction::kUint32);
continue;
}
// This phi is not safe, some operands are not uint32 values.
return false;
}
}
return true;
}
// Remove kUint32 flag from the phi itself and its operands. If any operand
// was a phi marked with kUint32 place it into a worklist for
// transitive clearing of kUint32 flag.
void HUint32AnalysisPhase::UnmarkPhi(HPhi* phi, ZoneList<HPhi*>* worklist) {
phi->ClearFlag(HInstruction::kUint32);
for (int j = 0; j < phi->OperandCount(); j++) {
HValue* operand = phi->OperandAt(j);
if (operand->CheckFlag(HInstruction::kUint32)) {
operand->ClearFlag(HInstruction::kUint32);
if (operand->IsPhi()) {
worklist->Add(HPhi::cast(operand), zone());
}
}
}
}
void HUint32AnalysisPhase::UnmarkUnsafePhis() {
// No phis were collected. Nothing to do.
if (phis_.length() == 0) return;
// Worklist used to transitively clear kUint32 from phis that
// are used as arguments to other phis.
ZoneList<HPhi*> worklist(phis_.length(), zone());
// Phi can be used as a uint32 value if and only if
// all its operands are uint32 values and all its
// uses are uint32 safe.
// Iterate over collected phis and unmark those that
// are unsafe. When unmarking phi unmark its operands
// and add it to the worklist if it is a phi as well.
// Phis that are still marked as safe are shifted down
// so that all safe phis form a prefix of the phis_ array.
int phi_count = 0;
for (int i = 0; i < phis_.length(); i++) {
HPhi* phi = phis_[i];
if (CheckPhiOperands(phi) && Uint32UsesAreSafe(phi)) {
phis_[phi_count++] = phi;
} else {
UnmarkPhi(phi, &worklist);
}
}
// Now phis array contains only those phis that have safe
// non-phi uses. Start transitively clearing kUint32 flag
// from phi operands of discovered non-safe phis until
// only safe phis are left.
while (!worklist.is_empty()) {
while (!worklist.is_empty()) {
HPhi* phi = worklist.RemoveLast();
UnmarkPhi(phi, &worklist);
}
// Check if any operands to safe phis were unmarked
// turning a safe phi into unsafe. The same value
// can flow into several phis.
int new_phi_count = 0;
for (int i = 0; i < phi_count; i++) {
HPhi* phi = phis_[i];
if (CheckPhiOperands(phi)) {
phis_[new_phi_count++] = phi;
} else {
UnmarkPhi(phi, &worklist);
}
}
phi_count = new_phi_count;
}
}
void HUint32AnalysisPhase::Run() {
if (!graph()->has_uint32_instructions()) return;
ZoneList<HInstruction*>* uint32_instructions = graph()->uint32_instructions();
for (int i = 0; i < uint32_instructions->length(); ++i) {
// Analyze instruction and mark it with kUint32 if all
// its uses are uint32 safe.
HInstruction* current = uint32_instructions->at(i);
if (current->IsLinked() &&
current->representation().IsInteger32() &&
Uint32UsesAreSafe(current)) {
current->SetFlag(HInstruction::kUint32);
}
}
// Some phis might have been optimistically marked with kUint32 flag.
// Remove this flag from those phis that are unsafe and propagate
// this information transitively potentially clearing kUint32 flag
// from some non-phi operations that are used as operands to unsafe phis.
UnmarkUnsafePhis();
}
} } // namespace v8::internal