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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-representation-changes.h"
namespace v8 {
namespace internal {
void HRepresentationChangesPhase::InsertRepresentationChangeForUse(
HValue* value, HValue* use_value, int use_index, Representation to) {
// Insert the representation change right before its use. For phi-uses we
// insert at the end of the corresponding predecessor.
HInstruction* next = NULL;
if (use_value->IsPhi()) {
next = use_value->block()->predecessors()->at(use_index)->end();
} else {
next = HInstruction::cast(use_value);
}
// For constants we try to make the representation change at compile
// time. When a representation change is not possible without loss of
// information we treat constants like normal instructions and insert the
// change instructions for them.
HInstruction* new_value = NULL;
bool is_truncating_to_smi = use_value->CheckFlag(HValue::kTruncatingToSmi);
bool is_truncating_to_int = use_value->CheckFlag(HValue::kTruncatingToInt32);
if (value->IsConstant()) {
HConstant* constant = HConstant::cast(value);
// Try to create a new copy of the constant with the new representation.
if (is_truncating_to_int && to.IsInteger32()) {
Maybe<HConstant*> res = constant->CopyToTruncatedInt32(graph()->zone());
if (res.has_value) new_value = res.value;
} else {
new_value = constant->CopyToRepresentation(to, graph()->zone());
}
}
if (new_value == NULL) {
new_value = new(graph()->zone()) HChange(
value, to, is_truncating_to_smi, is_truncating_to_int);
if (!use_value->operand_position(use_index).IsUnknown()) {
new_value->set_position(use_value->operand_position(use_index));
} else {
DCHECK(!FLAG_hydrogen_track_positions ||
!graph()->info()->IsOptimizing());
}
}
new_value->InsertBefore(next);
use_value->SetOperandAt(use_index, new_value);
}
static bool IsNonDeoptingIntToSmiChange(HChange* change) {
Representation from_rep = change->from();
Representation to_rep = change->to();
// Flags indicating Uint32 operations are set in a later Hydrogen phase.
DCHECK(!change->CheckFlag(HValue::kUint32));
return from_rep.IsInteger32() && to_rep.IsSmi() && SmiValuesAre32Bits();
}
void HRepresentationChangesPhase::InsertRepresentationChangesForValue(
HValue* value) {
Representation r = value->representation();
if (r.IsNone()) {
#ifdef DEBUG
for (HUseIterator it(value->uses()); !it.Done(); it.Advance()) {
HValue* use_value = it.value();
int use_index = it.index();
Representation req = use_value->RequiredInputRepresentation(use_index);
DCHECK(req.IsNone());
}
#endif
return;
}
if (value->HasNoUses()) {
if (value->IsForceRepresentation()) value->DeleteAndReplaceWith(NULL);
return;
}
for (HUseIterator it(value->uses()); !it.Done(); it.Advance()) {
HValue* use_value = it.value();
int use_index = it.index();
Representation req = use_value->RequiredInputRepresentation(use_index);
if (req.IsNone() || req.Equals(r)) continue;
// If this is an HForceRepresentation instruction, and an HChange has been
// inserted above it, examine the input representation of the HChange. If
// that's int32, and this HForceRepresentation use is int32, and int32 to
// smi changes can't cause deoptimisation, set the input of the use to the
// input of the HChange.
if (value->IsForceRepresentation()) {
HValue* input = HForceRepresentation::cast(value)->value();
if (input->IsChange()) {
HChange* change = HChange::cast(input);
if (change->from().Equals(req) && IsNonDeoptingIntToSmiChange(change)) {
use_value->SetOperandAt(use_index, change->value());
continue;
}
}
}
InsertRepresentationChangeForUse(value, use_value, use_index, req);
}
if (value->HasNoUses()) {
DCHECK(value->IsConstant() || value->IsForceRepresentation());
value->DeleteAndReplaceWith(NULL);
} else {
// The only purpose of a HForceRepresentation is to represent the value
// after the (possible) HChange instruction. We make it disappear.
if (value->IsForceRepresentation()) {
value->DeleteAndReplaceWith(HForceRepresentation::cast(value)->value());
}
}
}
void HRepresentationChangesPhase::Run() {
// Compute truncation flag for phis: Initially assume that all
// int32-phis allow truncation and iteratively remove the ones that
// are used in an operation that does not allow a truncating
// conversion.
ZoneList<HPhi*> int_worklist(8, zone());
ZoneList<HPhi*> smi_worklist(8, zone());
const ZoneList<HPhi*>* phi_list(graph()->phi_list());
for (int i = 0; i < phi_list->length(); i++) {
HPhi* phi = phi_list->at(i);
if (phi->representation().IsInteger32()) {
phi->SetFlag(HValue::kTruncatingToInt32);
} else if (phi->representation().IsSmi()) {
phi->SetFlag(HValue::kTruncatingToSmi);
phi->SetFlag(HValue::kTruncatingToInt32);
}
}
for (int i = 0; i < phi_list->length(); i++) {
HPhi* phi = phi_list->at(i);
HValue* value = NULL;
if (phi->representation().IsSmiOrInteger32() &&
!phi->CheckUsesForFlag(HValue::kTruncatingToInt32, &value)) {
int_worklist.Add(phi, zone());
phi->ClearFlag(HValue::kTruncatingToInt32);
if (FLAG_trace_representation) {
PrintF("#%d Phi is not truncating Int32 because of #%d %s\n",
phi->id(), value->id(), value->Mnemonic());
}
}
if (phi->representation().IsSmi() &&
!phi->CheckUsesForFlag(HValue::kTruncatingToSmi, &value)) {
smi_worklist.Add(phi, zone());
phi->ClearFlag(HValue::kTruncatingToSmi);
if (FLAG_trace_representation) {
PrintF("#%d Phi is not truncating Smi because of #%d %s\n",
phi->id(), value->id(), value->Mnemonic());
}
}
}
while (!int_worklist.is_empty()) {
HPhi* current = int_worklist.RemoveLast();
for (int i = 0; i < current->OperandCount(); ++i) {
HValue* input = current->OperandAt(i);
if (input->IsPhi() &&
input->representation().IsSmiOrInteger32() &&
input->CheckFlag(HValue::kTruncatingToInt32)) {
if (FLAG_trace_representation) {
PrintF("#%d Phi is not truncating Int32 because of #%d %s\n",
input->id(), current->id(), current->Mnemonic());
}
input->ClearFlag(HValue::kTruncatingToInt32);
int_worklist.Add(HPhi::cast(input), zone());
}
}
}
while (!smi_worklist.is_empty()) {
HPhi* current = smi_worklist.RemoveLast();
for (int i = 0; i < current->OperandCount(); ++i) {
HValue* input = current->OperandAt(i);
if (input->IsPhi() &&
input->representation().IsSmi() &&
input->CheckFlag(HValue::kTruncatingToSmi)) {
if (FLAG_trace_representation) {
PrintF("#%d Phi is not truncating Smi because of #%d %s\n",
input->id(), current->id(), current->Mnemonic());
}
input->ClearFlag(HValue::kTruncatingToSmi);
smi_worklist.Add(HPhi::cast(input), zone());
}
}
}
const ZoneList<HBasicBlock*>* blocks(graph()->blocks());
for (int i = 0; i < blocks->length(); ++i) {
// Process phi instructions first.
const HBasicBlock* block(blocks->at(i));
const ZoneList<HPhi*>* phis = block->phis();
for (int j = 0; j < phis->length(); j++) {
InsertRepresentationChangesForValue(phis->at(j));
}
// Process normal instructions.
for (HInstruction* current = block->first(); current != NULL; ) {
HInstruction* next = current->next();
InsertRepresentationChangesForValue(current);
current = next;
}
}
}
} } // namespace v8::internal