bool
Loop::optimize()
{
InstructionQueue invariantInstructions;
InstructionQueue boundsChecks;
IonSpew(IonSpew_LICM, "These instructions are in the loop: ");
while (!worklist_.empty()) {
if (mir->shouldCancel("LICM (worklist)"))
return false;
MInstruction *ins = popFromWorklist();
IonSpewHeader(IonSpew_LICM);
if (IonSpewEnabled(IonSpew_LICM)) {
ins->printName(IonSpewFile);
fprintf(IonSpewFile, " <- ");
ins->printOpcode(IonSpewFile);
fprintf(IonSpewFile, ": ");
}
if (isLoopInvariant(ins)) {
// Flag this instruction as loop invariant.
ins->setLoopInvariant();
if (!invariantInstructions.append(ins))
return false;
// Loop through uses of invariant instruction and add back to work list.
for (MUseDefIterator iter(ins->toDefinition()); iter; iter++) {
MDefinition *consumer = iter.def();
if (consumer->isInWorklist())
continue;
// if the consumer of this invariant instruction is in the
// loop, and it is also worth hoisting, then process it.
if (isInLoop(consumer) && isHoistable(consumer)) {
if (!insertInWorklist(consumer->toInstruction()))
return false;
}
}
if (IonSpewEnabled(IonSpew_LICM))
fprintf(IonSpewFile, " Loop Invariant!\n");
} else if (ins->isBoundsCheck()) {
if (!boundsChecks.append(ins))
return false;
}
}
if (!hoistInstructions(invariantInstructions, boundsChecks))
return false;
return true;
}
bool
Loop::optimize()
{
InstructionQueue invariantInstructions;
IonSpew(IonSpew_LICM, "These instructions are in the loop: ");
while (!worklist_.empty()) {
if (mir->shouldCancel("LICM (worklist)"))
return false;
MInstruction *ins = popFromWorklist();
IonSpewHeader(IonSpew_LICM);
if (IonSpewEnabled(IonSpew_LICM)) {
ins->printName(IonSpewFile);
fprintf(IonSpewFile, " <- ");
ins->printOpcode(IonSpewFile);
fprintf(IonSpewFile, ": ");
}
if (isLoopInvariant(ins)) {
// Flag this instruction as loop invariant.
ins->setLoopInvariant();
if (!invariantInstructions.append(ins))
return false;
if (IonSpewEnabled(IonSpew_LICM))
fprintf(IonSpewFile, " Loop Invariant!\n");
}
}
if (!hoistInstructions(invariantInstructions))
return false;
return true;
}
bool
Loop::hoistInstructions(InstructionQueue &toHoist, InstructionQueue &boundsChecks)
{
// Hoist bounds checks first, so that hoistBoundsCheck can test for
// invariant instructions, but delay actual insertion until the end to
// handle dependencies on loop invariant instructions.
InstructionQueue hoistedChecks;
for (size_t i = 0; i < boundsChecks.length(); i++) {
MBoundsCheck *ins = boundsChecks[i]->toBoundsCheck();
if (isLoopInvariant(ins) || !isInLoop(ins))
continue;
// Try to find a test dominating the bounds check which can be
// transformed into a hoistable check. Stop after the first such check
// which could be transformed (the one which will be the closest to the
// access in the source).
MBasicBlock *block = ins->block();
while (true) {
BranchDirection direction;
MTest *branch = block->immediateDominatorBranch(&direction);
if (branch) {
MInstruction *upper, *lower;
tryHoistBoundsCheck(ins, branch, direction, &upper, &lower);
if (upper && !hoistedChecks.append(upper))
return false;
if (lower && !hoistedChecks.append(lower))
return false;
if (upper || lower) {
ins->block()->discard(ins);
break;
}
}
MBasicBlock *dom = block->immediateDominator();
if (dom == block)
break;
block = dom;
}
}
// 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 (checkHotness(ins->block())) {
ins->block()->moveBefore(preLoop_->lastIns(), ins);
ins->setNotLoopInvariant();
}
}
for (size_t i = 0; i < hoistedChecks.length(); i++) {
MInstruction *ins = hoistedChecks[i];
preLoop_->insertBefore(preLoop_->lastIns(), ins);
}
return true;
}
