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// Copyright 2013 the V8 project authors. All rights reserved.
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are
// met:
//
// * Redistributions of source code must retain the above copyright
// notice, this list of conditions and the following disclaimer.
// * Redistributions in binary form must reproduce the above
// copyright notice, this list of conditions and the following
// disclaimer in the documentation and/or other materials provided
// with the distribution.
// * Neither the name of Google Inc. nor the names of its
// contributors may be used to endorse or promote products derived
// from this software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
#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->IsLeaveInlined()) {
// Never fold simulates from inlined environments into simulates
// in the outer environment.
// (Before each HEnterInlined, there is a non-foldable HSimulate
// anyway, so we get the barrier in the other direction for free.)
// 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->previous()->HasObservableSideEffects() &&
!current_simulate->next()->IsSimulate()) ||
!current_simulate->is_candidate_for_removal()) {
// This simulate is not suitable for folding.
// Fold the ones accumulated so far.
current_simulate->MergeWith(&mergelist);
continue;
} 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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