// Remove the CFG edge between |pred| and |block|, after releasing the phi
// operands on that edge and discarding any definitions consequently made dead.
bool
ValueNumberer::removePredecessorAndDoDCE(MBasicBlock *block, MBasicBlock *pred)
{
MOZ_ASSERT(!block->isMarked(),
"Block marked unreachable should have predecessors removed already");
// Before removing the predecessor edge, scan the phi operands for that edge
// for dead code before they get removed.
if (!block->phisEmpty()) {
uint32_t index = pred->positionInPhiSuccessor();
for (MPhiIterator iter(block->phisBegin()), end(block->phisEnd()); iter != end; ++iter) {
MPhi *phi = *iter;
MOZ_ASSERT(!values_.has(phi), "Visited phi in block having predecessor removed");
MDefinition *op = phi->getOperand(index);
if (op == phi)
continue;
// Set the operand to the phi itself rather than just releasing it
// because removePredecessor expects to have something to release.
phi->replaceOperand(index, phi);
if (!handleUseReleased(op, DontSetUseRemoved) || !processDeadDefs())
return false;
}
}
block->removePredecessor(pred);
return true;
}
// Remove the CFG edge between |pred| and |block|, after releasing the phi
// operands on that edge and discarding any definitions consequently made dead.
bool
ValueNumberer::removePredecessorAndDoDCE(MBasicBlock* block, MBasicBlock* pred, size_t predIndex)
{
MOZ_ASSERT(!block->isMarked(),
"Block marked unreachable should have predecessors removed already");
// Before removing the predecessor edge, scan the phi operands for that edge
// for dead code before they get removed.
MOZ_ASSERT(nextDef_ == nullptr);
for (MPhiIterator iter(block->phisBegin()), end(block->phisEnd()); iter != end; ) {
MPhi* phi = *iter++;
MOZ_ASSERT(!values_.has(phi), "Visited phi in block having predecessor removed");
MDefinition* op = phi->getOperand(predIndex);
phi->removeOperand(predIndex);
nextDef_ = iter != end ? *iter : nullptr;
if (!handleUseReleased(op, DontSetUseRemoved) || !processDeadDefs())
return false;
// If |nextDef_| became dead while we had it pinned, advance the iterator
// and discard it now.
while (nextDef_ && !nextDef_->hasUses()) {
phi = nextDef_->toPhi();
iter++;
nextDef_ = iter != end ? *iter : nullptr;
discardDefsRecursively(phi);
}
}
nextDef_ = nullptr;
block->removePredecessorWithoutPhiOperands(pred, predIndex);
return true;
}
void
MBasicBlock::inheritPhis(MBasicBlock *header)
{
MResumePoint *headerRp = header->entryResumePoint();
size_t stackDepth = headerRp->numOperands();
for (size_t slot = 0; slot < stackDepth; slot++) {
MDefinition *exitDef = getSlot(slot);
MDefinition *loopDef = headerRp->getOperand(slot);
if (!loopDef->isPhi()) {
MOZ_ASSERT(loopDef->block()->id() < header->id());
MOZ_ASSERT(loopDef == exitDef);
continue;
}
// Phis are allocated by NewPendingLoopHeader.
MPhi *phi = loopDef->toPhi();
MOZ_ASSERT(phi->numOperands() == 2);
// The entry definition is always the leftmost input to the phi.
MDefinition *entryDef = phi->getOperand(0);
if (entryDef != exitDef)
continue;
// If the entryDef is the same as exitDef, then we must propagate the
// phi down to this successor. This chance was missed as part of
// setBackedge() because exits are not captured in resume points.
setSlot(slot, phi);
}
}
// Remove the CFG edge between |pred| and |block|, after releasing the phi
// operands on that edge and discarding any definitions consequently made dead.
bool
ValueNumberer::removePredecessorAndDoDCE(MBasicBlock *block, MBasicBlock *pred, size_t predIndex)
{
MOZ_ASSERT(!block->isMarked(),
"Block marked unreachable should have predecessors removed already");
// Before removing the predecessor edge, scan the phi operands for that edge
// for dead code before they get removed.
MOZ_ASSERT(nextDef_ == nullptr);
for (MPhiIterator iter(block->phisBegin()), end(block->phisEnd()); iter != end; ) {
MPhi *phi = *iter++;
MOZ_ASSERT(!values_.has(phi), "Visited phi in block having predecessor removed");
MDefinition *op = phi->getOperand(predIndex);
phi->removeOperand(predIndex);
nextDef_ = *iter;
if (!handleUseReleased(op, DontSetUseRemoved) || !processDeadDefs())
return false;
}
nextDef_ = nullptr;
block->removePredecessorWithoutPhiOperands(pred, predIndex);
return true;
}
// Determine whether the possible value of start (a phi node within the loop)
// can become smaller than an initial value at loop entry.
bool
Loop::nonDecreasing(MDefinition *initial, MDefinition *start)
{
MDefinitionVector worklist;
MDefinitionVector seen;
if (!worklist.append(start))
return false;
while (!worklist.empty()) {
MDefinition *def = worklist.popCopy();
bool duplicate = false;
for (size_t i = 0; i < seen.length() && !duplicate; i++) {
if (seen[i] == def)
duplicate = true;
}
if (duplicate)
continue;
if (!seen.append(def))
return false;
if (def->type() != MIRType_Int32)
return false;
if (!isInLoop(def)) {
if (def != initial)
return false;
continue;
}
if (def->isPhi()) {
MPhi *phi = def->toPhi();
for (size_t i = 0; i < phi->numOperands(); i++) {
if (!worklist.append(phi->getOperand(i)))
return false;
}
continue;
}
if (def->isAdd()) {
if (def->toAdd()->specialization() != MIRType_Int32)
return false;
MDefinition *lhs = def->toAdd()->getOperand(0);
MDefinition *rhs = def->toAdd()->getOperand(1);
if (!rhs->isConstant())
return false;
Value v = rhs->toConstant()->value();
if (!v.isInt32() || v.toInt32() < 0)
return false;
if (!worklist.append(lhs))
return false;
continue;
}
return false;
}
return true;
}
AbortReason
MBasicBlock::setBackedge(MBasicBlock *pred)
{
// Predecessors must be finished, and at the correct stack depth.
JS_ASSERT(lastIns_);
JS_ASSERT(pred->lastIns_);
JS_ASSERT(pred->stackDepth() == entryResumePoint()->stackDepth());
// We must be a pending loop header
JS_ASSERT(kind_ == PENDING_LOOP_HEADER);
bool hadTypeChange = false;
// Add exit definitions to each corresponding phi at the entry.
for (MPhiIterator phi = phisBegin(); phi != phisEnd(); phi++) {
MPhi *entryDef = *phi;
MDefinition *exitDef = pred->slots_[entryDef->slot()];
// Assert that we already placed phis for each slot.
JS_ASSERT(entryDef->block() == this);
if (entryDef == exitDef) {
// If the exit def is the same as the entry def, make a redundant
// phi. Since loop headers have exactly two incoming edges, we
// know that that's just the first input.
//
// Note that we eliminate later rather than now, to avoid any
// weirdness around pending continue edges which might still hold
// onto phis.
exitDef = entryDef->getOperand(0);
}
bool typeChange = false;
if (!entryDef->addInputSlow(exitDef, &typeChange))
return AbortReason_Alloc;
hadTypeChange |= typeChange;
JS_ASSERT(entryDef->slot() < pred->stackDepth());
setSlot(entryDef->slot(), entryDef);
}
if (hadTypeChange) {
for (MPhiIterator phi = phisBegin(); phi != phisEnd(); phi++)
phi->removeOperand(phi->numOperands() - 1);
return AbortReason_Disable;
}
// We are now a loop header proper
kind_ = LOOP_HEADER;
if (!predecessors_.append(pred))
return AbortReason_Alloc;
return AbortReason_NoAbort;
}
bool
MBasicBlock::inheritPhisFromBackedge(MBasicBlock* backedge, bool* hadTypeChange)
{
// We must be a pending loop header
MOZ_ASSERT(kind_ == PENDING_LOOP_HEADER);
size_t stackDepth = entryResumePoint()->stackDepth();
for (size_t slot = 0; slot < stackDepth; slot++) {
// Get the value stack-slot of the back edge.
MDefinition* exitDef = backedge->getSlot(slot);
// Get the value of the loop header.
MDefinition* loopDef = entryResumePoint()->getOperand(slot);
if (loopDef->block() != this) {
// If we are finishing a pending loop header, then we need to ensure
// that all operands are phis. This is usualy the case, except for
// object/arrays build with generators, in which case we share the
// same allocations across all blocks.
MOZ_ASSERT(loopDef->block()->id() < id());
MOZ_ASSERT(loopDef == exitDef);
continue;
}
// Phis are allocated by NewPendingLoopHeader.
MPhi* entryDef = loopDef->toPhi();
MOZ_ASSERT(entryDef->block() == this);
if (entryDef == exitDef) {
// If the exit def is the same as the entry def, make a redundant
// phi. Since loop headers have exactly two incoming edges, we
// know that that's just the first input.
//
// Note that we eliminate later rather than now, to avoid any
// weirdness around pending continue edges which might still hold
// onto phis.
exitDef = entryDef->getOperand(0);
}
bool typeChange = false;
if (!entryDef->addInputSlow(exitDef))
return false;
if (!entryDef->checkForTypeChange(exitDef, &typeChange))
return false;
*hadTypeChange |= typeChange;
setSlot(slot, entryDef);
}
return true;
}
bool
MBasicBlock::setBackedgeWasm(MBasicBlock* pred)
{
// Predecessors must be finished, and at the correct stack depth.
MOZ_ASSERT(hasLastIns());
MOZ_ASSERT(pred->hasLastIns());
MOZ_ASSERT(stackDepth() == pred->stackDepth());
// We must be a pending loop header
MOZ_ASSERT(kind_ == PENDING_LOOP_HEADER);
// Add exit definitions to each corresponding phi at the entry.
// Note: Phis are inserted in the same order as the slots. (see
// MBasicBlock::New)
size_t slot = 0;
for (MPhiIterator phi = phisBegin(); phi != phisEnd(); phi++, slot++) {
MPhi* entryDef = *phi;
MDefinition* exitDef = pred->getSlot(slot);
// Assert that we already placed phis for each slot.
MOZ_ASSERT(entryDef->block() == this);
// Assert that the phi already has the correct type.
MOZ_ASSERT(entryDef->type() == exitDef->type());
MOZ_ASSERT(entryDef->type() != MIRType::Value);
if (entryDef == exitDef) {
// If the exit def is the same as the entry def, make a redundant
// phi. Since loop headers have exactly two incoming edges, we
// know that that's just the first input.
//
// Note that we eliminate later rather than now, to avoid any
// weirdness around pending continue edges which might still hold
// onto phis.
exitDef = entryDef->getOperand(0);
}
// Phis always have room for 2 operands, so this can't fail.
MOZ_ASSERT(phi->numOperands() == 1);
entryDef->addInlineInput(exitDef);
MOZ_ASSERT(slot < pred->stackDepth());
setSlot(slot, entryDef);
}
// We are now a loop header proper
kind_ = LOOP_HEADER;
return predecessors_.append(pred);
}
void
MBasicBlock::setLoopHeader(MBasicBlock* newBackedge)
{
MOZ_ASSERT(!isLoopHeader());
kind_ = LOOP_HEADER;
size_t numPreds = numPredecessors();
MOZ_ASSERT(numPreds != 0);
size_t lastIndex = numPreds - 1;
size_t oldIndex = 0;
for (; ; ++oldIndex) {
MOZ_ASSERT(oldIndex < numPreds);
MBasicBlock* pred = getPredecessor(oldIndex);
if (pred == newBackedge)
break;
}
// Set the loop backedge to be the last element in predecessors_.
Swap(predecessors_[oldIndex], predecessors_[lastIndex]);
// If we have phis, reorder their operands accordingly.
if (!phisEmpty()) {
getPredecessor(oldIndex)->setSuccessorWithPhis(this, oldIndex);
getPredecessor(lastIndex)->setSuccessorWithPhis(this, lastIndex);
for (MPhiIterator iter(phisBegin()), end(phisEnd()); iter != end; ++iter) {
MPhi* phi = *iter;
MDefinition* last = phi->getOperand(oldIndex);
MDefinition* old = phi->getOperand(lastIndex);
phi->replaceOperand(oldIndex, old);
phi->replaceOperand(lastIndex, last);
}
}
MOZ_ASSERT(newBackedge->loopHeaderOfBackedge() == this);
MOZ_ASSERT(backedge() == newBackedge);
}
bool
MBasicBlock::setBackedgeAsmJS(MBasicBlock *pred)
{
// Predecessors must be finished, and at the correct stack depth.
JS_ASSERT(lastIns_);
JS_ASSERT(pred->lastIns_);
JS_ASSERT(stackDepth() == pred->stackDepth());
// We must be a pending loop header
JS_ASSERT(kind_ == PENDING_LOOP_HEADER);
// Add exit definitions to each corresponding phi at the entry.
for (MPhiIterator phi = phisBegin(); phi != phisEnd(); phi++) {
MPhi *entryDef = *phi;
MDefinition *exitDef = pred->getSlot(entryDef->slot());
// Assert that we already placed phis for each slot.
JS_ASSERT(entryDef->block() == this);
// Assert that the phi already has the correct type.
JS_ASSERT(entryDef->type() == exitDef->type());
JS_ASSERT(entryDef->type() != MIRType_Value);
if (entryDef == exitDef) {
// If the exit def is the same as the entry def, make a redundant
// phi. Since loop headers have exactly two incoming edges, we
// know that that's just the first input.
//
// Note that we eliminate later rather than now, to avoid any
// weirdness around pending continue edges which might still hold
// onto phis.
exitDef = entryDef->getOperand(0);
}
// MBasicBlock::NewAsmJS calls reserveLength(2) for loop header phis.
entryDef->addInput(exitDef);
JS_ASSERT(entryDef->slot() < pred->stackDepth());
setSlot(entryDef->slot(), entryDef);
}
// We are now a loop header proper
kind_ = LOOP_HEADER;
return predecessors_.append(pred);
}
void
MBasicBlock::inheritPhis(MBasicBlock *header)
{
for (MPhiIterator iter = header->phisBegin(); iter != header->phisEnd(); iter++) {
MPhi *phi = *iter;
JS_ASSERT(phi->numOperands() == 2);
// The entry definition is always the leftmost input to the phi.
MDefinition *entryDef = phi->getOperand(0);
MDefinition *exitDef = getSlot(phi->slot());
if (entryDef != exitDef)
continue;
// If the entryDef is the same as exitDef, then we must propagate the
// phi down to this successor. This chance was missed as part of
// setBackedge() because exits are not captured in resume points.
setSlot(phi->slot(), phi);
}
}
bool
MBasicBlock::setBackedge(MBasicBlock *pred)
{
// Predecessors must be finished, and at the correct stack depth.
JS_ASSERT(lastIns_);
JS_ASSERT(pred->lastIns_);
JS_ASSERT(pred->stackDepth() == entryResumePoint()->stackDepth());
// We must be a pending loop header
JS_ASSERT(kind_ == PENDING_LOOP_HEADER);
// Add exit definitions to each corresponding phi at the entry.
for (uint32_t i = 0; i < pred->stackDepth(); i++) {
MPhi *entryDef = entryResumePoint()->getOperand(i)->toPhi();
MDefinition *exitDef = pred->slots_[i];
// Assert that we already placed phis for each slot.
JS_ASSERT(entryDef->block() == this);
if (entryDef == exitDef) {
// If the exit def is the same as the entry def, make a redundant
// phi. Since loop headers have exactly two incoming edges, we
// know that that's just the first input.
//
// Note that we eliminate later rather than now, to avoid any
// weirdness around pending continue edges which might still hold
// onto phis.
exitDef = entryDef->getOperand(0);
}
if (!entryDef->addInput(exitDef))
return false;
setSlot(i, entryDef);
}
// We are now a loop header proper
kind_ = LOOP_HEADER;
return predecessors_.append(pred);
}
void
LoopUnroller::go(LoopIterationBound *bound)
{
// For now we always unroll loops the same number of times.
static const size_t UnrollCount = 10;
JitSpew(JitSpew_Unrolling, "Attempting to unroll loop");
header = bound->header;
// UCE might have determined this isn't actually a loop.
if (!header->isLoopHeader())
return;
backedge = header->backedge();
oldPreheader = header->loopPredecessor();
JS_ASSERT(oldPreheader->numSuccessors() == 1);
// Only unroll loops with two blocks: an initial one ending with the
// bound's test, and the body ending with the backedge.
MTest *test = bound->test;
if (header->lastIns() != test)
return;
if (test->ifTrue() == backedge) {
if (test->ifFalse()->id() <= backedge->id())
return;
} else if (test->ifFalse() == backedge) {
if (test->ifTrue()->id() <= backedge->id())
return;
} else {
return;
}
if (backedge->numPredecessors() != 1 || backedge->numSuccessors() != 1)
return;
JS_ASSERT(backedge->phisEmpty());
MBasicBlock *bodyBlocks[] = { header, backedge };
// All instructions in the header and body must be clonable.
for (size_t i = 0; i < ArrayLength(bodyBlocks); i++) {
MBasicBlock *block = bodyBlocks[i];
for (MInstructionIterator iter(block->begin()); iter != block->end(); iter++) {
MInstruction *ins = *iter;
if (ins->canClone())
continue;
if (ins->isTest() || ins->isGoto() || ins->isInterruptCheck())
continue;
#ifdef DEBUG
JitSpew(JitSpew_Unrolling, "Aborting: can't clone instruction %s", ins->opName());
#endif
return;
}
}
// Compute the linear inequality we will use for exiting the unrolled loop:
//
// iterationBound - iterationCount - UnrollCount >= 0
//
LinearSum remainingIterationsInequality(bound->boundSum);
if (!remainingIterationsInequality.add(bound->currentSum, -1))
return;
if (!remainingIterationsInequality.add(-int32_t(UnrollCount)))
return;
// Terms in the inequality need to be either loop invariant or phis from
// the original header.
for (size_t i = 0; i < remainingIterationsInequality.numTerms(); i++) {
MDefinition *def = remainingIterationsInequality.term(i).term;
if (def->block()->id() < header->id())
continue;
if (def->block() == header && def->isPhi())
continue;
return;
}
// OK, we've checked everything, now unroll the loop.
JitSpew(JitSpew_Unrolling, "Unrolling loop");
// The old preheader will go before the unrolled loop, and the old loop
// will need a new empty preheader.
CompileInfo &info = oldPreheader->info();
if (header->trackedSite().pc()) {
unrolledHeader =
MBasicBlock::New(graph, nullptr, info,
oldPreheader, header->trackedSite(), MBasicBlock::LOOP_HEADER);
unrolledBackedge =
MBasicBlock::New(graph, nullptr, info,
unrolledHeader, backedge->trackedSite(), MBasicBlock::NORMAL);
newPreheader =
MBasicBlock::New(graph, nullptr, info,
unrolledHeader, oldPreheader->trackedSite(), MBasicBlock::NORMAL);
} else {
unrolledHeader = MBasicBlock::NewAsmJS(graph, info, oldPreheader, MBasicBlock::LOOP_HEADER);
unrolledBackedge = MBasicBlock::NewAsmJS(graph, info, unrolledHeader, MBasicBlock::NORMAL);
newPreheader = MBasicBlock::NewAsmJS(graph, info, unrolledHeader, MBasicBlock::NORMAL);
}
unrolledHeader->discardAllResumePoints();
unrolledBackedge->discardAllResumePoints();
newPreheader->discardAllResumePoints();
// Insert new blocks at their RPO position, and update block ids.
graph.insertBlockAfter(oldPreheader, unrolledHeader);
graph.insertBlockAfter(unrolledHeader, unrolledBackedge);
graph.insertBlockAfter(unrolledBackedge, newPreheader);
graph.renumberBlocksAfter(oldPreheader);
if (!unrolledDefinitions.init())
CrashAtUnhandlableOOM("LoopUnroller::go");
// Add phis to the unrolled loop header which correspond to the phis in the
// original loop header.
JS_ASSERT(header->getPredecessor(0) == oldPreheader);
for (MPhiIterator iter(header->phisBegin()); iter != header->phisEnd(); iter++) {
MPhi *old = *iter;
JS_ASSERT(old->numOperands() == 2);
MPhi *phi = MPhi::New(alloc);
phi->setResultType(old->type());
phi->setResultTypeSet(old->resultTypeSet());
phi->setRange(old->range());
unrolledHeader->addPhi(phi);
if (!phi->reserveLength(2))
CrashAtUnhandlableOOM("LoopUnroller::go");
// Set the first input for the phi for now. We'll set the second after
// finishing the unroll.
phi->addInput(old->getOperand(0));
// The old phi will now take the value produced by the unrolled loop.
old->replaceOperand(0, phi);
if (!unrolledDefinitions.putNew(old, phi))
CrashAtUnhandlableOOM("LoopUnroller::go");
}
// The loop condition can bail out on e.g. integer overflow, so make a
// resume point based on the initial resume point of the original header.
MResumePoint *headerResumePoint = header->entryResumePoint();
if (headerResumePoint) {
MResumePoint *rp = makeReplacementResumePoint(unrolledHeader, headerResumePoint);
unrolledHeader->setEntryResumePoint(rp);
// Perform an interrupt check at the start of the unrolled loop.
unrolledHeader->add(MInterruptCheck::New(alloc));
}
// Generate code for the test in the unrolled loop.
for (size_t i = 0; i < remainingIterationsInequality.numTerms(); i++) {
MDefinition *def = remainingIterationsInequality.term(i).term;
MDefinition *replacement = getReplacementDefinition(def);
remainingIterationsInequality.replaceTerm(i, replacement);
}
MCompare *compare = ConvertLinearInequality(alloc, unrolledHeader, remainingIterationsInequality);
MTest *unrolledTest = MTest::New(alloc, compare, unrolledBackedge, newPreheader);
unrolledHeader->end(unrolledTest);
// Make an entry resume point for the unrolled body. The unrolled header
// does not have side effects on stack values, even if the original loop
// header does, so use the same resume point as for the unrolled header.
if (headerResumePoint) {
MResumePoint *rp = makeReplacementResumePoint(unrolledBackedge, headerResumePoint);
unrolledBackedge->setEntryResumePoint(rp);
}
// Make an entry resume point for the new preheader. There are no
// instructions which use this but some other stuff wants one to be here.
if (headerResumePoint) {
MResumePoint *rp = makeReplacementResumePoint(newPreheader, headerResumePoint);
newPreheader->setEntryResumePoint(rp);
}
// Generate the unrolled code.
JS_ASSERT(UnrollCount > 1);
size_t unrollIndex = 0;
while (true) {
// Clone the contents of the original loop into the unrolled loop body.
for (size_t i = 0; i < ArrayLength(bodyBlocks); i++) {
MBasicBlock *block = bodyBlocks[i];
for (MInstructionIterator iter(block->begin()); iter != block->end(); iter++) {
MInstruction *ins = *iter;
if (ins->canClone()) {
makeReplacementInstruction(*iter);
} else {
// Control instructions are handled separately.
JS_ASSERT(ins->isTest() || ins->isGoto() || ins->isInterruptCheck());
}
}
}
// Compute the value of each loop header phi after the execution of
// this unrolled iteration.
MDefinitionVector phiValues(alloc);
JS_ASSERT(header->getPredecessor(1) == backedge);
for (MPhiIterator iter(header->phisBegin()); iter != header->phisEnd(); iter++) {
MPhi *old = *iter;
MDefinition *oldInput = old->getOperand(1);
if (!phiValues.append(getReplacementDefinition(oldInput)))
CrashAtUnhandlableOOM("LoopUnroller::go");
}
unrolledDefinitions.clear();
if (unrollIndex == UnrollCount - 1) {
// We're at the end of the last unrolled iteration, set the
// backedge input for the unrolled loop phis.
size_t phiIndex = 0;
for (MPhiIterator iter(unrolledHeader->phisBegin()); iter != unrolledHeader->phisEnd(); iter++) {
MPhi *phi = *iter;
phi->addInput(phiValues[phiIndex++]);
}
JS_ASSERT(phiIndex == phiValues.length());
break;
}
// Update the map for the phis in the next iteration.
size_t phiIndex = 0;
for (MPhiIterator iter(header->phisBegin()); iter != header->phisEnd(); iter++) {
MPhi *old = *iter;
if (!unrolledDefinitions.putNew(old, phiValues[phiIndex++]))
CrashAtUnhandlableOOM("LoopUnroller::go");
}
JS_ASSERT(phiIndex == phiValues.length());
unrollIndex++;
}
MGoto *backedgeJump = MGoto::New(alloc, unrolledHeader);
unrolledBackedge->end(backedgeJump);
// Place the old preheader before the unrolled loop.
JS_ASSERT(oldPreheader->lastIns()->isGoto());
oldPreheader->discardLastIns();
oldPreheader->end(MGoto::New(alloc, unrolledHeader));
// Place the new preheader before the original loop.
newPreheader->end(MGoto::New(alloc, header));
// Cleanup the MIR graph.
if (!unrolledHeader->addPredecessorWithoutPhis(unrolledBackedge))
CrashAtUnhandlableOOM("LoopUnroller::go");
header->replacePredecessor(oldPreheader, newPreheader);
oldPreheader->setSuccessorWithPhis(unrolledHeader, 0);
newPreheader->setSuccessorWithPhis(header, 0);
unrolledBackedge->setSuccessorWithPhis(unrolledHeader, 1);
}
bool
ion::EliminatePhis(MIRGenerator *mir, MIRGraph &graph)
{
Vector<MPhi *, 16, SystemAllocPolicy> worklist;
// Add all observable phis to a worklist. We use the "in worklist" bit to
// mean "this phi is live".
for (PostorderIterator block = graph.poBegin(); block != graph.poEnd(); block++) {
if (mir->shouldCancel("Eliminate Phis (populate loop)"))
return false;
MPhiIterator iter = block->phisBegin();
while (iter != block->phisEnd()) {
// Flag all as unused, only observable phis would be marked as used
// when processed by the work list.
iter->setUnused();
// If the phi is redundant, remove it here.
if (MDefinition *redundant = IsPhiRedundant(*iter)) {
iter->replaceAllUsesWith(redundant);
iter = block->discardPhiAt(iter);
continue;
}
// Enqueue observable Phis.
if (IsPhiObservable(*iter)) {
iter->setInWorklist();
if (!worklist.append(*iter))
return false;
}
iter++;
}
}
// Iteratively mark all phis reachable from live phis.
while (!worklist.empty()) {
if (mir->shouldCancel("Eliminate Phis (worklist)"))
return false;
MPhi *phi = worklist.popCopy();
JS_ASSERT(phi->isUnused());
phi->setNotInWorklist();
// The removal of Phis can produce newly redundant phis.
if (MDefinition *redundant = IsPhiRedundant(phi)) {
// Add to the worklist the used phis which are impacted.
for (MUseDefIterator it(phi); it; it++) {
if (it.def()->isPhi()) {
MPhi *use = it.def()->toPhi();
if (!use->isUnused()) {
use->setUnusedUnchecked();
use->setInWorklist();
if (!worklist.append(use))
return false;
}
}
}
phi->replaceAllUsesWith(redundant);
} else {
// Otherwise flag them as used.
phi->setNotUnused();
}
// The current phi is/was used, so all its operands are used.
for (size_t i = 0; i < phi->numOperands(); i++) {
MDefinition *in = phi->getOperand(i);
if (!in->isPhi() || !in->isUnused() || in->isInWorklist())
continue;
in->setInWorklist();
if (!worklist.append(in->toPhi()))
return false;
}
}
// Sweep dead phis.
for (PostorderIterator block = graph.poBegin(); block != graph.poEnd(); block++) {
MPhiIterator iter = block->phisBegin();
while (iter != block->phisEnd()) {
if (iter->isUnused())
iter = block->discardPhiAt(iter);
else
iter++;
}
}
return true;
}
bool
ion::EliminatePhis(MIRGenerator *mir, MIRGraph &graph,
Observability observe)
{
// Eliminates redundant or unobservable phis from the graph. A
// redundant phi is something like b = phi(a, a) or b = phi(a, b),
// both of which can be replaced with a. An unobservable phi is
// one that whose value is never used in the program.
//
// Note that we must be careful not to eliminate phis representing
// values that the interpreter will require later. When the graph
// is first constructed, we can be more aggressive, because there
// is a greater correspondence between the CFG and the bytecode.
// After optimizations such as GVN have been performed, however,
// the bytecode and CFG may not correspond as closely to one
// another. In that case, we must be more conservative. The flag
// |conservativeObservability| is used to indicate that eliminate
// phis is being run after some optimizations have been performed,
// and thus we should use more conservative rules about
// observability. The particular danger is that we can optimize
// away uses of a phi because we think they are not executable,
// but the foundation for that assumption is false TI information
// that will eventually be invalidated. Therefore, if
// |conservativeObservability| is set, we will consider any use
// from a resume point to be observable. Otherwise, we demand a
// use from an actual instruction.
Vector<MPhi *, 16, SystemAllocPolicy> worklist;
// Add all observable phis to a worklist. We use the "in worklist" bit to
// mean "this phi is live".
for (PostorderIterator block = graph.poBegin(); block != graph.poEnd(); block++) {
if (mir->shouldCancel("Eliminate Phis (populate loop)"))
return false;
MPhiIterator iter = block->phisBegin();
while (iter != block->phisEnd()) {
// Flag all as unused, only observable phis would be marked as used
// when processed by the work list.
iter->setUnused();
// If the phi is redundant, remove it here.
if (MDefinition *redundant = IsPhiRedundant(*iter)) {
iter->replaceAllUsesWith(redundant);
iter = block->discardPhiAt(iter);
continue;
}
// Enqueue observable Phis.
if (IsPhiObservable(*iter, observe)) {
iter->setInWorklist();
if (!worklist.append(*iter))
return false;
}
iter++;
}
}
// Iteratively mark all phis reachable from live phis.
while (!worklist.empty()) {
if (mir->shouldCancel("Eliminate Phis (worklist)"))
return false;
MPhi *phi = worklist.popCopy();
JS_ASSERT(phi->isUnused());
phi->setNotInWorklist();
// The removal of Phis can produce newly redundant phis.
if (MDefinition *redundant = IsPhiRedundant(phi)) {
// Add to the worklist the used phis which are impacted.
for (MUseDefIterator it(phi); it; it++) {
if (it.def()->isPhi()) {
MPhi *use = it.def()->toPhi();
if (!use->isUnused()) {
use->setUnusedUnchecked();
use->setInWorklist();
if (!worklist.append(use))
return false;
}
}
}
phi->replaceAllUsesWith(redundant);
} else {
// Otherwise flag them as used.
phi->setNotUnused();
}
// The current phi is/was used, so all its operands are used.
for (size_t i = 0; i < phi->numOperands(); i++) {
MDefinition *in = phi->getOperand(i);
if (!in->isPhi() || !in->isUnused() || in->isInWorklist())
continue;
in->setInWorklist();
if (!worklist.append(in->toPhi()))
return false;
}
}
// Sweep dead phis.
for (PostorderIterator block = graph.poBegin(); block != graph.poEnd(); block++) {
MPhiIterator iter = block->phisBegin();
while (iter != block->phisEnd()) {
if (iter->isUnused())
iter = block->discardPhiAt(iter);
else
iter++;
}
}
return true;
}
