void
MBasicBlock::flagOperandsOfPrunedBranches(MInstruction* ins)
{
// Find the previous resume point which would be used for bailing out.
MResumePoint* rp = nullptr;
for (MInstructionReverseIterator iter = rbegin(ins); iter != rend(); iter++) {
rp = iter->resumePoint();
if (rp)
break;
}
// If none, take the entry resume point.
if (!rp)
rp = entryResumePoint();
// The only blocks which do not have any entryResumePoint in Ion, are the
// SplitEdge blocks. SplitEdge blocks only have a Goto instruction before
// Range Analysis phase. In adjustInputs, we are manipulating instructions
// which have a TypePolicy. So, as a Goto has no operand and no type
// policy, the entry resume point should exists.
MOZ_ASSERT(rp);
// Flag all operand as being potentially used.
while (rp) {
for (size_t i = 0, end = rp->numOperands(); i < end; i++)
rp->getOperand(i)->setUseRemovedUnchecked();
rp = rp->caller();
}
}
// Instructions are useless if they are unused and have no side effects.
// This pass eliminates useless instructions.
// The graph itself is unchanged.
bool
ion::EliminateDeadCode(MIRGenerator *mir, MIRGraph &graph)
{
// Traverse in postorder so that we hit uses before definitions.
// Traverse instruction list backwards for the same reason.
for (PostorderIterator block = graph.poBegin(); block != graph.poEnd(); block++) {
if (mir->shouldCancel("Eliminate Dead Code (main loop)"))
return false;
// Remove unused instructions.
for (MInstructionReverseIterator inst = block->rbegin(); inst != block->rend(); ) {
if (!inst->isEffectful() && !inst->resumePoint() &&
!inst->hasUses() && !inst->isGuard() &&
!inst->isControlInstruction()) {
inst = block->discardAt(inst);
} else {
inst++;
}
}
}
return true;
}