bool
Loop::hoistInstructions(InstructionQueue &toHoist)
{
// Iterate in post-order (uses before definitions)
for (int32_t i = toHoist.length() - 1; i >= 0; i--) {
MInstruction *ins = toHoist[i];
// Don't hoist MConstantElements, MConstant and MBox
// if it doesn't enable us to hoist one of its uses.
// We want those instructions as close as possible to their use.
if (ins->isConstantElements() || ins->isConstant() || ins->isBox()) {
bool loopInvariantUse = false;
for (MUseDefIterator use(ins); use; use++) {
if (use.def()->isLoopInvariant()) {
loopInvariantUse = true;
break;
}
}
if (!loopInvariantUse)
ins->setNotLoopInvariant();
}
}
// Move all instructions to the preLoop_ block just before the control instruction.
for (size_t i = 0; i < toHoist.length(); i++) {
MInstruction *ins = toHoist[i];
// Loads may have an implicit dependency on either stores (effectful instructions) or
// control instructions so we should never move these.
JS_ASSERT(!ins->isControlInstruction());
JS_ASSERT(!ins->isEffectful());
JS_ASSERT(ins->isMovable());
if (!ins->isLoopInvariant())
continue;
if (checkHotness(ins->block())) {
ins->block()->moveBefore(preLoop_->lastIns(), ins);
ins->setNotLoopInvariant();
}
}
return true;
}
