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[turbofan] don't take hints from deferred blocks

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We should prefer hints from operands in non-deferred blocks, else we
risk sideways moves on the hot path, just to accommodate the register
allocator's choice of register assignment in the deferred block.

BUG=

Review URL: https://codereview.chromium.org/1718223002

Cr-Commit-Position: refs/heads/master@{#34296}
This commit is contained in:
mtrofin 2016-02-25 07:40:46 -08:00 committed by Commit bot
parent c5142d863b
commit ac9f182746
1 changed files with 16 additions and 2 deletions
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18
src/compiler/register-allocator.cc
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@ -2197,8 +2197,22 @@ void LiveRangeBuilder::ProcessPhis(const InstructionBlock* block,
int phi_vreg = phi->virtual_register();
live->Remove(phi_vreg);
InstructionOperand* hint = nullptr;
Instruction* instr = GetLastInstruction(
code(), code()->InstructionBlockAt(block->predecessors()[0]));
const InstructionBlock::Predecessors& predecessors = block->predecessors();
const InstructionBlock* predecessor_block =
code()->InstructionBlockAt(predecessors[0]);
const Instruction* instr = GetLastInstruction(code(), predecessor_block);
if (predecessor_block->IsDeferred()) {
// "Prefer the hint from the first non-deferred predecessor, if any.
for (size_t i = 1; i < predecessors.size(); ++i) {
predecessor_block = code()->InstructionBlockAt(predecessors[i]);
if (!predecessor_block->IsDeferred()) {
instr = GetLastInstruction(code(), predecessor_block);
break;
}
}
}
DCHECK_NOT_NULL(instr);
for (MoveOperands* move : *instr->GetParallelMove(Instruction::END)) {
InstructionOperand& to = move->destination();
if (to.IsUnallocated() &&