bool
UnreachableCodeElimination::removeUnmarkedBlocksAndClearDominators()
{
// Removes blocks that are not marked from the graph. For blocks
// that *are* marked, clears the mark and adjusts the id to its
// new value. Also adds blocks that are immediately reachable
// from an unmarked block to the frontier.
size_t id = marked_;
for (PostorderIterator iter(graph_.poBegin()); iter != graph_.poEnd();) {
if (mir_->shouldCancel("Eliminate Unreachable Code"))
return false;
MBasicBlock *block = *iter;
iter++;
// Unconditionally clear the dominators. It's somewhat complex to
// adjust the values and relatively fast to just recompute.
block->clearDominatorInfo();
if (block->isMarked()) {
block->setId(--id);
for (MPhiIterator iter(block->phisBegin()); iter != block->phisEnd(); iter++)
checkDependencyAndRemoveUsesFromUnmarkedBlocks(*iter);
for (MInstructionIterator iter(block->begin()); iter != block->end(); iter++)
checkDependencyAndRemoveUsesFromUnmarkedBlocks(*iter);
} else {
for (size_t i = 0, c = block->numSuccessors(); i < c; i++) {
MBasicBlock *succ = block->getSuccessor(i);
if (succ->isMarked()) {
// succ is on the frontier of blocks to be removed:
succ->removePredecessor(block);
if (!redundantPhis_) {
for (MPhiIterator iter(succ->phisBegin()); iter != succ->phisEnd(); iter++) {
if (iter->operandIfRedundant()) {
redundantPhis_ = true;
break;
}
}
}
}
}
graph_.removeBlock(block);
}
}
JS_ASSERT(id == 0);
return true;
}
bool
UnreachableCodeElimination::removeUnmarkedBlocksAndClearDominators()
{
// Removes blocks that are not marked from the graph. For blocks
// that *are* marked, clears the mark and adjusts the id to its
// new value. Also adds blocks that are immediately reachable
// from an unmarked block to the frontier.
size_t id = marked_;
for (PostorderIterator iter(graph_.poBegin()); iter != graph_.poEnd();) {
if (mir_->shouldCancel("Eliminate Unreachable Code"))
return false;
MBasicBlock *block = *iter;
iter++;
// Unconditionally clear the dominators. It's somewhat complex to
// adjust the values and relatively fast to just recompute.
block->clearDominatorInfo();
if (block->isMarked()) {
block->setId(--id);
for (MPhiIterator iter(block->phisBegin()); iter != block->phisEnd(); iter++)
checkDependencyAndRemoveUsesFromUnmarkedBlocks(*iter);
for (MInstructionIterator iter(block->begin()); iter != block->end(); iter++)
checkDependencyAndRemoveUsesFromUnmarkedBlocks(*iter);
} else {
if (block->numPredecessors() > 1) {
// If this block had phis, then any reachable
// predecessors need to have the successorWithPhis
// flag cleared.
for (size_t i = 0; i < block->numPredecessors(); i++)
block->getPredecessor(i)->setSuccessorWithPhis(nullptr, 0);
}
if (block->isLoopBackedge()) {
// NB. We have to update the loop header if we
// eliminate the backedge. At first I thought this
// check would be insufficient, because it would be
// possible to have code like this:
//
// while (true) {
// ...;
// if (1 == 1) break;
// }
//
// in which the backedge is removed as part of
// rewriting the condition, but no actual blocks are
// removed. However, in all such cases, the backedge
// would be a critical edge and hence the critical
// edge block is being removed.
block->loopHeaderOfBackedge()->clearLoopHeader();
}
for (size_t i = 0, c = block->numSuccessors(); i < c; i++) {
MBasicBlock *succ = block->getSuccessor(i);
if (succ->isMarked()) {
// succ is on the frontier of blocks to be removed:
succ->removePredecessor(block);
if (!redundantPhis_) {
for (MPhiIterator iter(succ->phisBegin()); iter != succ->phisEnd(); iter++) {
if (iter->operandIfRedundant()) {
redundantPhis_ = true;
break;
}
}
}
}
}
// When we remove a call, we can't leave the corresponding MPassArg
// in the graph. Since lowering will fail. Replace it with the
// argument for the exceptional case when it is kept alive in a
// ResumePoint. DCE will remove the unused MPassArg instruction.
for (MInstructionIterator iter(block->begin()); iter != block->end(); iter++) {
if (iter->isCall()) {
MCall *call = iter->toCall();
for (size_t i = 0; i < call->numStackArgs(); i++) {
JS_ASSERT(call->getArg(i)->isPassArg());
JS_ASSERT(call->getArg(i)->hasOneDefUse());
MPassArg *arg = call->getArg(i)->toPassArg();
arg->replaceAllUsesWith(arg->getArgument());
}
}
}
graph_.removeBlock(block);
}
}
JS_ASSERT(id == 0);
return true;
}
