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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 "hydrogen-removable-simulates.h"
namespace v8 {
namespace internal {
void HMergeRemovableSimulatesPhase::Run() {
ZoneList<HSimulate*> mergelist(2, zone());
for (int i = 0; i < graph()->blocks()->length(); ++i) {
HBasicBlock* block = graph()->blocks()->at(i);
// Make sure the merge list is empty at the start of a block.
ASSERT(mergelist.is_empty());
// Nasty heuristic: Never remove the first simulate in a block. This
// just so happens to have a beneficial effect on register allocation.
bool first = true;
for (HInstructionIterator it(block); !it.Done(); it.Advance()) {
HInstruction* current = it.Current();
if (current->IsEnterInlined()) {
// Ensure there's a non-foldable HSimulate before an HEnterInlined to
// avoid folding across HEnterInlined.
ASSERT(!HSimulate::cast(current->previous())->
is_candidate_for_removal());
}
if (current->IsLeaveInlined()) {
// Never fold simulates from inlined environments into simulates in the
// outer environment. Simply remove all accumulated simulates without
// merging. This is safe because simulates after instructions with side
// effects are never added to the merge list.
while (!mergelist.is_empty()) {
mergelist.RemoveLast()->DeleteAndReplaceWith(NULL);
}
continue;
}
if (current->IsReturn()) {
// Drop mergeable simulates in the list. This is safe because
// simulates after instructions with side effects are never added
// to the merge list.
while (!mergelist.is_empty()) {
mergelist.RemoveLast()->DeleteAndReplaceWith(NULL);
}
continue;
}
// Skip the non-simulates and the first simulate.
if (!current->IsSimulate()) continue;
if (first) {
first = false;
continue;
}
HSimulate* current_simulate = HSimulate::cast(current);
if (!current_simulate->is_candidate_for_removal()) {
current_simulate->MergeWith(&mergelist);
} else if (current_simulate->ast_id().IsNone()) {
ASSERT(current_simulate->next()->IsEnterInlined());
if (!mergelist.is_empty()) {
HSimulate* last = mergelist.RemoveLast();
last->MergeWith(&mergelist);
}
} else if (current_simulate->previous()->HasObservableSideEffects()) {
while (current_simulate->next()->IsSimulate()) {
it.Advance();
HSimulate* next_simulate = HSimulate::cast(it.Current());
if (next_simulate->ast_id().IsNone()) break;
mergelist.Add(current_simulate, zone());
current_simulate = next_simulate;
if (!current_simulate->is_candidate_for_removal()) break;
}
current_simulate->MergeWith(&mergelist);
} else {
// Accumulate this simulate for folding later on.
mergelist.Add(current_simulate, zone());
}
}
if (!mergelist.is_empty()) {
// Merge the accumulated simulates at the end of the block.
HSimulate* last = mergelist.RemoveLast();
last->MergeWith(&mergelist);
}
}
}
} } // namespace v8::internal
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