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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-infer-representation.h"
namespace v8 {
namespace internal {
void HInferRepresentationPhase::AddToWorklist(HValue* current) {
if (current->representation().IsTagged()) return;
if (!current->CheckFlag(HValue::kFlexibleRepresentation)) return;
if (in_worklist_.Contains(current->id())) return;
worklist_.Add(current, zone());
in_worklist_.Add(current->id());
}
void HInferRepresentationPhase::Run() {
// (1) Initialize bit vectors and count real uses. Each phi gets a
// bit-vector of length <number of phis>.
const ZoneList<HPhi*>* phi_list = graph()->phi_list();
int phi_count = phi_list->length();
ZoneList<BitVector*> connected_phis(phi_count, zone());
for (int i = 0; i < phi_count; ++i) {
phi_list->at(i)->InitRealUses(i);
BitVector* connected_set = new(zone()) BitVector(phi_count, zone());
connected_set->Add(i);
connected_phis.Add(connected_set, zone());
}
// (2) Do a fixed point iteration to find the set of connected phis. A
// phi is connected to another phi if its value is used either directly or
// indirectly through a transitive closure of the def-use relation.
bool change = true;
while (change) {
change = false;
// We normally have far more "forward edges" than "backward edges",
// so we terminate faster when we walk backwards.
for (int i = phi_count - 1; i >= 0; --i) {
HPhi* phi = phi_list->at(i);
for (HUseIterator it(phi->uses()); !it.Done(); it.Advance()) {
HValue* use = it.value();
if (use->IsPhi()) {
int id = HPhi::cast(use)->phi_id();
if (connected_phis[i]->UnionIsChanged(*connected_phis[id]))
change = true;
}
}
}
}
// Set truncation flags for groups of connected phis. This is a conservative
// approximation; the flag will be properly re-computed after representations
// have been determined.
if (phi_count > 0) {
BitVector done(phi_count, zone());
for (int i = 0; i < phi_count; ++i) {
if (done.Contains(i)) continue;
// Check if all uses of all connected phis in this group are truncating.
bool all_uses_everywhere_truncating_int32 = true;
bool all_uses_everywhere_truncating_smi = true;
for (BitVector::Iterator it(connected_phis[i]);
!it.Done();
it.Advance()) {
int index = it.Current();
all_uses_everywhere_truncating_int32 &=
phi_list->at(index)->CheckFlag(HInstruction::kTruncatingToInt32);
all_uses_everywhere_truncating_smi &=
phi_list->at(index)->CheckFlag(HInstruction::kTruncatingToSmi);
done.Add(index);
}
if (!all_uses_everywhere_truncating_int32) {
// Clear truncation flag of this group of connected phis.
for (BitVector::Iterator it(connected_phis[i]);
!it.Done();
it.Advance()) {
int index = it.Current();
phi_list->at(index)->ClearFlag(HInstruction::kTruncatingToInt32);
}
}
if (!all_uses_everywhere_truncating_smi) {
// Clear truncation flag of this group of connected phis.
for (BitVector::Iterator it(connected_phis[i]);
!it.Done();
it.Advance()) {
int index = it.Current();
phi_list->at(index)->ClearFlag(HInstruction::kTruncatingToSmi);
}
}
}
}
// Simplify constant phi inputs where possible.
// This step uses kTruncatingToInt32 flags of phis.
for (int i = 0; i < phi_count; ++i) {
phi_list->at(i)->SimplifyConstantInputs();
}
// Use the phi reachability information from step 2 to
// sum up the non-phi use counts of all connected phis.
for (int i = 0; i < phi_count; ++i) {
HPhi* phi = phi_list->at(i);
for (BitVector::Iterator it(connected_phis[i]);
!it.Done();
it.Advance()) {
int index = it.Current();
HPhi* it_use = phi_list->at(index);
if (index != i) phi->AddNonPhiUsesFrom(it_use); // Don't count twice.
}
}
// Initialize work list
for (int i = 0; i < graph()->blocks()->length(); ++i) {
HBasicBlock* block = graph()->blocks()->at(i);
const ZoneList<HPhi*>* phis = block->phis();
for (int j = 0; j < phis->length(); ++j) {
AddToWorklist(phis->at(j));
}
for (HInstructionIterator it(block); !it.Done(); it.Advance()) {
HInstruction* current = it.Current();
AddToWorklist(current);
}
}
// Do a fixed point iteration, trying to improve representations
while (!worklist_.is_empty()) {
HValue* current = worklist_.RemoveLast();
current->InferRepresentation(this);
in_worklist_.Remove(current->id());
}
// Lastly: any instruction that we don't have representation information
// for defaults to Tagged.
for (int i = 0; i < graph()->blocks()->length(); ++i) {
HBasicBlock* block = graph()->blocks()->at(i);
const ZoneList<HPhi*>* phis = block->phis();
for (int j = 0; j < phis->length(); ++j) {
HPhi* phi = phis->at(j);
if (phi->representation().IsNone()) {
phi->ChangeRepresentation(Representation::Tagged());
}
}
for (HInstructionIterator it(block); !it.Done(); it.Advance()) {
HInstruction* current = it.Current();
if (current->representation().IsNone() &&
current->CheckFlag(HInstruction::kFlexibleRepresentation)) {
if (current->CheckFlag(HInstruction::kCannotBeTagged)) {
current->ChangeRepresentation(Representation::Double());
} else {
current->ChangeRepresentation(Representation::Tagged());
}
}
}
}
}
} } // namespace v8::internal
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