void
MBasicBlock::removePredecessor(MBasicBlock *pred)
{
// If we're removing the last backedge, this is no longer a loop.
if (isLoopHeader() && hasUniqueBackedge() && backedge() == pred)
clearLoopHeader();
for (size_t i = 0; i < numPredecessors(); i++) {
if (getPredecessor(i) != pred)
continue;
// Adjust phis. Note that this can leave redundant phis
// behind.
if (!phisEmpty()) {
JS_ASSERT(pred->successorWithPhis());
JS_ASSERT(pred->positionInPhiSuccessor() == i);
for (MPhiIterator iter = phisBegin(); iter != phisEnd(); iter++)
iter->removeOperand(i);
pred->setSuccessorWithPhis(nullptr, 0);
for (size_t j = i+1; j < numPredecessors(); j++)
getPredecessor(j)->setSuccessorWithPhis(this, j - 1);
}
// Remove from pred list.
MBasicBlock **ptr = predecessors_.begin() + i;
predecessors_.erase(ptr);
return;
}
MOZ_ASSUME_UNREACHABLE("predecessor was not found");
}
void
MBasicBlock::removePredecessor(MBasicBlock *pred)
{
JS_ASSERT(numPredecessors() >= 2);
for (size_t i = 0; i < numPredecessors(); i++) {
if (getPredecessor(i) != pred)
continue;
// Adjust phis. Note that this can leave redundant phis
// behind.
if (!phisEmpty()) {
JS_ASSERT(pred->successorWithPhis());
JS_ASSERT(pred->positionInPhiSuccessor() == i);
for (MPhiIterator iter = phisBegin(); iter != phisEnd(); iter++)
iter->removeOperand(i);
for (size_t j = i+1; j < numPredecessors(); j++)
getPredecessor(j)->setSuccessorWithPhis(this, j - 1);
}
// Remove from pred list.
MBasicBlock **ptr = predecessors_.begin() + i;
predecessors_.erase(ptr);
return;
}
JS_NOT_REACHED("predecessor was not found");
}
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.
if (!inheritPhisFromBackedge(pred, &hadTypeChange))
return AbortReason_Alloc;
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;
}
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;
}
void
MBasicBlock::discardAllPhiOperands()
{
for (MPhiIterator iter = phisBegin(); iter != phisEnd(); iter++)
iter->removeAllOperands();
for (MBasicBlock **pred = predecessors_.begin(); pred != predecessors_.end(); pred++)
(*pred)->setSuccessorWithPhis(nullptr, 0);
}
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);
}
MPhiIterator
MBasicBlock::discardPhiAt(MPhiIterator &at)
{
JS_ASSERT(!phis_.empty());
for (size_t i = 0; i < at->numOperands(); i++)
at->discardOperand(i);
MPhiIterator result = phis_.removeAt(at);
if (phis_.empty()) {
for (MBasicBlock **pred = predecessors_.begin(); pred != predecessors_.end(); pred++)
(*pred)->setSuccessorWithPhis(NULL, 0);
}
return result;
}
void
MBasicBlock::addPredecessorSameInputsAs(MBasicBlock* pred, MBasicBlock* existingPred)
{
MOZ_ASSERT(pred);
MOZ_ASSERT(predecessors_.length() > 0);
// Predecessors must be finished, and at the correct stack depth.
MOZ_ASSERT(pred->hasLastIns());
MOZ_ASSERT(!pred->successorWithPhis());
if (!phisEmpty()) {
size_t existingPosition = indexForPredecessor(existingPred);
for (MPhiIterator iter = phisBegin(); iter != phisEnd(); iter++) {
if (!iter->addInputSlow(iter->getOperand(existingPosition)))
CrashAtUnhandlableOOM("MBasicBlock::addPredecessorAdjustPhis");
}
}
if (!predecessors_.append(pred))
CrashAtUnhandlableOOM("MBasicBlock::addPredecessorAdjustPhis");
}
MPhiIterator
MBasicBlock::discardPhiAt(MPhiIterator &at)
{
JS_ASSERT(!phis_.empty());
at->removeAllOperands();
MPhiIterator result = phis_.removeAt(at);
if (phis_.empty()) {
for (MBasicBlock **pred = predecessors_.begin(); pred != predecessors_.end(); pred++)
(*pred)->setSuccessorWithPhis(nullptr, 0);
}
return result;
}
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;
}
