void
JSONSpewer::spewMResumePoint(MResumePoint *rp)
{
if (!rp)
return;
beginObjectProperty("resumePoint");
if (rp->caller())
integerProperty("caller", rp->caller()->block()->id());
property("mode");
switch (rp->mode()) {
case MResumePoint::ResumeAt:
fprintf(fp_, "\"At\"");
break;
case MResumePoint::ResumeAfter:
fprintf(fp_, "\"After\"");
break;
case MResumePoint::Outer:
fprintf(fp_, "\"Outer\"");
break;
}
beginListProperty("operands");
for (MResumePoint *iter = rp; iter; iter = iter->caller()) {
for (int i = iter->numOperands() - 1; i >= 0; i--)
integerValue(iter->getOperand(i)->id());
if (iter->caller())
stringValue("|");
}
endList();
endObject();
}
// Do not optimize any Phi instruction which has conflicting Unbox operations,
// as this might imply some intended polymorphism.
static bool
CanUnboxSimdPhi(const JitCompartment* jitCompartment, MPhi* phi, SimdType unboxType)
{
MOZ_ASSERT(phi->type() == MIRType::Object);
// If we are unboxing, we are more than likely to have boxed this SIMD type
// once in baseline, otherwise, we cannot create a MSimdBox as we have no
// template object to use.
if (!jitCompartment->maybeGetSimdTemplateObjectFor(unboxType))
return false;
MResumePoint* entry = phi->block()->entryResumePoint();
MIRType mirType = SimdTypeToMIRType(unboxType);
for (MUseIterator i(phi->usesBegin()), e(phi->usesEnd()); i != e; i++) {
// If we cannot recover the Simd object at the entry of the basic block,
// then we would have to box the content anyways.
if ((*i)->consumer() == entry && !entry->isRecoverableOperand(*i))
return false;
if (!(*i)->consumer()->isDefinition())
continue;
MDefinition* def = (*i)->consumer()->toDefinition();
if (def->isSimdUnbox() && def->toSimdUnbox()->type() != mirType)
return false;
}
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);
}
}
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();
}
}
LSnapshot *
LIRGeneratorShared::buildSnapshot(LInstruction *ins, MResumePoint *rp, BailoutKind kind)
{
LSnapshot *snapshot = LSnapshot::New(gen, rp, kind);
if (!snapshot)
return NULL;
FlattenedMResumePointIter iter(rp);
if (!iter.init())
return NULL;
size_t i = 0;
for (MResumePoint **it = iter.begin(), **end = iter.end(); it != end; ++it) {
MResumePoint *mir = *it;
for (size_t j = 0; j < mir->numOperands(); ++i, ++j) {
MDefinition *def = mir->getOperand(j);
if (def->isPassArg())
def = def->toPassArg()->getArgument();
LAllocation *a = snapshot->getEntry(i);
if (def->isUnused()) {
*a = LConstantIndex::Bogus();
continue;
}
*a = useKeepaliveOrConstant(def);
}
}
return snapshot;
}
MResumePoint *
MResumePoint::New(MBasicBlock *block, jsbytecode *pc, MResumePoint *parent, Mode mode)
{
MResumePoint *resume = new MResumePoint(block, pc, parent, mode);
if (!resume->init(block))
return NULL;
resume->inherit(block);
return resume;
}
LSnapshot *
LIRGeneratorShared::buildSnapshot(LInstruction *ins, MResumePoint *rp, BailoutKind kind)
{
LSnapshot *snapshot = LSnapshot::New(gen, rp, kind);
if (!snapshot)
return NULL;
FlattenedMResumePointIter iter(rp);
if (!iter.init())
return NULL;
size_t i = 0;
for (MResumePoint **it = iter.begin(), **end = iter.end(); it != end; ++it) {
MResumePoint *mir = *it;
for (size_t j = 0, e = mir->numOperands(); j < e; ++i, ++j) {
MDefinition *ins = mir->getOperand(j);
LAllocation *type = snapshot->typeOfSlot(i);
LAllocation *payload = snapshot->payloadOfSlot(i);
if (ins->isPassArg())
ins = ins->toPassArg()->getArgument();
JS_ASSERT(!ins->isPassArg());
if (ins->isBox())
ins = ins->toBox()->getOperand(0);
// Guards should never be eliminated.
JS_ASSERT_IF(ins->isUnused(), !ins->isGuard());
// Snapshot operands other than constants should never be
// emitted-at-uses. Try-catch support depends on there being no
// code between an instruction and the LOsiPoint that follows it.
JS_ASSERT_IF(!ins->isConstant(), !ins->isEmittedAtUses());
// The register allocation will fill these fields in with actual
// register/stack assignments. During code generation, we can restore
// interpreter state with the given information. Note that for
// constants, including known types, we record a dummy placeholder,
// since we can recover the same information, much cleaner, from MIR.
if (ins->isConstant() || ins->isUnused()) {
*type = LConstantIndex::Bogus();
*payload = LConstantIndex::Bogus();
} else if (ins->type() != MIRType_Value) {
*type = LConstantIndex::Bogus();
*payload = use(ins, LUse::KEEPALIVE);
} else {
*type = useType(ins, LUse::KEEPALIVE);
*payload = usePayload(ins, LUse::KEEPALIVE);
}
}
}
return snapshot;
}
void
MBasicBlock::discardAllResumePoints(bool discardEntry)
{
for (MResumePointIterator iter = resumePointsBegin(); iter != resumePointsEnd(); ) {
MResumePoint *rp = *iter;
if (rp == entryResumePoint() && !discardEntry) {
iter++;
} else {
rp->discardUses();
iter = resumePoints_.removeAt(iter);
}
}
}
static bool
CheckUseImpliesOperand(MInstruction *ins, MUse *use)
{
MNode *consumer = use->consumer();
uint32_t index = use->index();
if (consumer->isDefinition()) {
MDefinition *def = consumer->toDefinition();
return (def->getOperand(index) == ins);
}
JS_ASSERT(consumer->isResumePoint());
MResumePoint *res = consumer->toResumePoint();
return (res->getOperand(index) == ins);
}
LSnapshot *
LIRGeneratorShared::buildSnapshot(LInstruction *ins, MResumePoint *rp, BailoutKind kind)
{
LSnapshot *snapshot = LSnapshot::New(gen, rp, kind);
if (!snapshot)
return NULL;
FlattenedMResumePointIter iter(rp);
if (!iter.init())
return NULL;
size_t i = 0;
for (MResumePoint **it = iter.begin(), **end = iter.end(); it != end; ++it) {
MResumePoint *mir = *it;
for (size_t j = 0, e = mir->numOperands(); j < e; ++i, ++j) {
MDefinition *def = mir->getOperand(j);
if (def->isPassArg())
def = def->toPassArg()->getArgument();
JS_ASSERT(!def->isPassArg());
if (def->isBox())
def = def->toBox()->getOperand(0);
// Guards should never be eliminated.
JS_ASSERT_IF(def->isUnused(), !def->isGuard());
// Snapshot operands other than constants should never be
// emitted-at-uses. Try-catch support depends on there being no
// code between an instruction and the LOsiPoint that follows it.
JS_ASSERT_IF(!def->isConstant(), !def->isEmittedAtUses());
LAllocation *a = snapshot->getEntry(i);
if (def->isUnused()) {
*a = LConstantIndex::Bogus();
continue;
}
*a = useKeepaliveOrConstant(def);
}
}
return snapshot;
}
bool
LRecoverInfo::init(MResumePoint *rp)
{
MResumePoint *it = rp;
// Sort operations in the order in which we need to restore the stack. This
// implies that outer frames, as well as operations needed to recover the
// current frame, are located before the current frame. The inner-most
// resume point should be the last element in the list.
do {
if (!instructions_.append(it))
return false;
it = it->caller();
} while (it);
Reverse(instructions_.begin(), instructions_.end());
MOZ_ASSERT(mir() == rp);
return true;
}
// Visit |def|.
bool
ValueNumberer::visitDefinition(MDefinition* def)
{
// Nop does not fit in any of the previous optimization, as its only purpose
// is to reduce the register pressure by keeping additional resume
// point. Still, there is no need consecutive list of MNop instructions, and
// this will slow down every other iteration on the Graph.
if (def->isNop()) {
MNop* nop = def->toNop();
MBasicBlock* block = nop->block();
// We look backward to know if we can remove the previous Nop, we do not
// look forward as we would not benefit from the folding made by GVN.
MInstructionReverseIterator iter = ++block->rbegin(nop);
// This nop is at the beginning of the basic block, just replace the
// resume point of the basic block by the one from the resume point.
if (iter == block->rend()) {
JitSpew(JitSpew_GVN, " Removing Nop%u", nop->id());
nop->moveResumePointAsEntry();
block->discard(nop);
return true;
}
// The previous instruction is also a Nop, no need to keep it anymore.
MInstruction* prev = *iter;
if (prev->isNop()) {
JitSpew(JitSpew_GVN, " Removing Nop%u", prev->id());
block->discard(prev);
return true;
}
// The Nop is introduced to capture the result and make sure the operands
// are not live anymore when there are no further uses. Though when
// all operands are still needed the Nop doesn't decrease the liveness
// and can get removed.
MResumePoint* rp = nop->resumePoint();
if (rp && rp->numOperands() > 0 &&
rp->getOperand(rp->numOperands() - 1) == prev &&
!nop->block()->lastIns()->isThrow())
{
size_t numOperandsLive = 0;
for (size_t j = 0; j < prev->numOperands(); j++) {
for (size_t i = 0; i < rp->numOperands(); i++) {
if (prev->getOperand(j) == rp->getOperand(i)) {
numOperandsLive++;
break;
}
}
}
if (numOperandsLive == prev->numOperands()) {
JitSpew(JitSpew_GVN, " Removing Nop%u", nop->id());
block->discard(nop);
}
}
return true;
}
// Skip optimizations on instructions which are recovered on bailout, to
// avoid mixing instructions which are recovered on bailouts with
// instructions which are not.
if (def->isRecoveredOnBailout())
return true;
// If this instruction has a dependency() into an unreachable block, we'll
// need to update AliasAnalysis.
MDefinition* dep = def->dependency();
if (dep != nullptr && (dep->isDiscarded() || dep->block()->isDead())) {
JitSpew(JitSpew_GVN, " AliasAnalysis invalidated");
if (updateAliasAnalysis_ && !dependenciesBroken_) {
// TODO: Recomputing alias-analysis could theoretically expose more
// GVN opportunities.
JitSpew(JitSpew_GVN, " Will recompute!");
dependenciesBroken_ = true;
}
// Temporarily clear its dependency, to protect foldsTo, which may
// wish to use the dependency to do store-to-load forwarding.
def->setDependency(def->toInstruction());
} else {
dep = nullptr;
}
// Look for a simplified form of |def|.
MDefinition* sim = simplified(def);
if (sim != def) {
if (sim == nullptr)
return false;
bool isNewInstruction = sim->block() == nullptr;
// If |sim| doesn't belong to a block, insert it next to |def|.
if (isNewInstruction)
def->block()->insertAfter(def->toInstruction(), sim->toInstruction());
#ifdef JS_JITSPEW
JitSpew(JitSpew_GVN, " Folded %s%u to %s%u",
def->opName(), def->id(), sim->opName(), sim->id());
#endif
MOZ_ASSERT(!sim->isDiscarded());
ReplaceAllUsesWith(def, sim);
// The node's foldsTo said |def| can be replaced by |rep|. If |def| is a
// guard, then either |rep| is also a guard, or a guard isn't actually
// needed, so we can clear |def|'s guard flag and let it be discarded.
def->setNotGuardUnchecked();
if (DeadIfUnused(def)) {
if (!discardDefsRecursively(def))
return false;
// If that ended up discarding |sim|, then we're done here.
if (sim->isDiscarded())
return true;
}
if (!rerun_ && def->isPhi() && !sim->isPhi()) {
rerun_ = true;
JitSpew(JitSpew_GVN, " Replacing phi%u may have enabled cascading optimisations; "
"will re-run", def->id());
}
// Otherwise, procede to optimize with |sim| in place of |def|.
def = sim;
// If the simplified instruction was already part of the graph, then we
// probably already visited and optimized this instruction.
if (!isNewInstruction)
return true;
}
// Now that foldsTo is done, re-enable the original dependency. Even though
// it may be pointing into a discarded block, it's still valid for the
// purposes of detecting congruent loads.
if (dep != nullptr)
def->setDependency(dep);
// Look for a dominating def which makes |def| redundant.
MDefinition* rep = leader(def);
if (rep != def) {
if (rep == nullptr)
return false;
if (rep->updateForReplacement(def)) {
#ifdef JS_JITSPEW
JitSpew(JitSpew_GVN,
" Replacing %s%u with %s%u",
def->opName(), def->id(), rep->opName(), rep->id());
#endif
ReplaceAllUsesWith(def, rep);
// The node's congruentTo said |def| is congruent to |rep|, and it's
// dominated by |rep|. If |def| is a guard, it's covered by |rep|,
// so we can clear |def|'s guard flag and let it be discarded.
def->setNotGuardUnchecked();
if (DeadIfUnused(def)) {
// discardDef should not add anything to the deadDefs, as the
// redundant operation should have the same input operands.
mozilla::DebugOnly<bool> r = discardDef(def);
MOZ_ASSERT(r, "discardDef shouldn't have tried to add anything to the worklist, "
"so it shouldn't have failed");
MOZ_ASSERT(deadDefs_.empty(),
"discardDef shouldn't have added anything to the worklist");
}
def = rep;
}
}
return true;
}
MBasicBlock*
MBasicBlock::NewSplitEdge(MIRGraph& graph, MBasicBlock* pred, size_t predEdgeIdx, MBasicBlock* succ)
{
MBasicBlock* split = nullptr;
if (!succ->pc()) {
// The predecessor does not have a PC, this is a Wasm compilation.
split = MBasicBlock::New(graph, succ->info(), pred, SPLIT_EDGE);
if (!split)
return nullptr;
} else {
// The predecessor has a PC, this is an IonBuilder compilation.
MResumePoint* succEntry = succ->entryResumePoint();
BytecodeSite* site = new(graph.alloc()) BytecodeSite(succ->trackedTree(), succEntry->pc());
split = new(graph.alloc()) MBasicBlock(graph, succ->info(), site, SPLIT_EDGE);
if (!split->init())
return nullptr;
// A split edge is used to simplify the graph to avoid having a
// predecessor with multiple successors as well as a successor with
// multiple predecessors. As instructions can be moved in this
// split-edge block, we need to give this block a resume point. To do
// so, we copy the entry resume points of the successor and filter the
// phis to keep inputs from the current edge.
// Propagate the caller resume point from the inherited block.
split->callerResumePoint_ = succ->callerResumePoint();
// Split-edge are created after the interpreter stack emulation. Thus,
// there is no need for creating slots.
split->stackPosition_ = succEntry->stackDepth();
// Create a resume point using our initial stack position.
MResumePoint* splitEntry = new(graph.alloc()) MResumePoint(split, succEntry->pc(),
MResumePoint::ResumeAt);
if (!splitEntry->init(graph.alloc()))
return nullptr;
split->entryResumePoint_ = splitEntry;
// The target entry resume point might have phi operands, keep the
// operands of the phi coming from our edge.
size_t succEdgeIdx = succ->indexForPredecessor(pred);
for (size_t i = 0, e = splitEntry->numOperands(); i < e; i++) {
MDefinition* def = succEntry->getOperand(i);
// This early in the pipeline, we have no recover instructions in
// any entry resume point.
MOZ_ASSERT_IF(def->block() == succ, def->isPhi());
if (def->block() == succ)
def = def->toPhi()->getOperand(succEdgeIdx);
splitEntry->initOperand(i, def);
}
// This is done in the New variant for wasm, so we cannot keep this
// line below, where the rest of the graph is modified.
if (!split->predecessors_.append(pred))
return nullptr;
}
split->setLoopDepth(succ->loopDepth());
// Insert the split edge block in-between.
split->end(MGoto::New(graph.alloc(), succ));
graph.insertBlockAfter(pred, split);
pred->replaceSuccessor(predEdgeIdx, split);
succ->replacePredecessor(pred, split);
return split;
}
// Operands to a resume point which are dead at the point of the resume can be
// replaced with undefined values. This analysis supports limited detection of
// dead operands, pruning those which are defined in the resume point's basic
// block and have no uses outside the block or at points later than the resume
// point.
//
// This is intended to ensure that extra resume points within a basic block
// will not artificially extend the lifetimes of any SSA values. This could
// otherwise occur if the new resume point captured a value which is created
// between the old and new resume point and is dead at the new resume point.
bool
ion::EliminateDeadResumePointOperands(MIRGenerator *mir, MIRGraph &graph)
{
for (PostorderIterator block = graph.poBegin(); block != graph.poEnd(); block++) {
if (mir->shouldCancel("Eliminate Dead Resume Point Operands (main loop)"))
return false;
// The logic below can get confused on infinite loops.
if (block->isLoopHeader() && block->backedge() == *block)
continue;
for (MInstructionIterator ins = block->begin(); ins != block->end(); ins++) {
// No benefit to replacing constant operands with other constants.
if (ins->isConstant())
continue;
// Scanning uses does not give us sufficient information to tell
// where instructions that are involved in box/unbox operations or
// parameter passing might be live. Rewriting uses of these terms
// in resume points may affect the interpreter's behavior. Rather
// than doing a more sophisticated analysis, just ignore these.
if (ins->isUnbox() || ins->isParameter())
continue;
// If the instruction's behavior has been constant folded into a
// separate instruction, we can't determine precisely where the
// instruction becomes dead and can't eliminate its uses.
if (ins->isFolded())
continue;
// Check if this instruction's result is only used within the
// current block, and keep track of its last use in a definition
// (not resume point). This requires the instructions in the block
// to be numbered, ensured by running this immediately after alias
// analysis.
uint32_t maxDefinition = 0;
for (MUseDefIterator uses(*ins); uses; uses++) {
if (uses.def()->block() != *block ||
uses.def()->isBox() ||
uses.def()->isPassArg() ||
uses.def()->isPhi())
{
maxDefinition = UINT32_MAX;
break;
}
maxDefinition = Max(maxDefinition, uses.def()->id());
}
if (maxDefinition == UINT32_MAX)
continue;
// Walk the uses a second time, removing any in resume points after
// the last use in a definition.
for (MUseIterator uses(ins->usesBegin()); uses != ins->usesEnd(); ) {
if (uses->node()->isDefinition()) {
uses++;
continue;
}
MResumePoint *mrp = uses->node()->toResumePoint();
if (mrp->block() != *block ||
!mrp->instruction() ||
mrp->instruction() == *ins ||
mrp->instruction()->id() <= maxDefinition)
{
uses++;
continue;
}
// Store an undefined value in place of all dead resume point
// operands. Making any such substitution can in general alter
// the interpreter's behavior, even though the code is dead, as
// the interpreter will still execute opcodes whose effects
// cannot be observed. If the undefined value were to flow to,
// say, a dead property access the interpreter could throw an
// exception; we avoid this problem by removing dead operands
// before removing dead code.
MConstant *constant = MConstant::New(UndefinedValue());
block->insertBefore(*(block->begin()), constant);
uses = mrp->replaceOperand(uses, constant);
}
}
}
return true;
}
