bool run()
{
ASSERT(m_graph.m_form == ThreadedCPS);
ASSERT(m_graph.m_unificationState == LocallyUnified);
// Ensure that all Phi functions are unified.
for (BlockIndex blockIndex = m_graph.m_blocks.size(); blockIndex--;) {
BasicBlock* block = m_graph.m_blocks[blockIndex].get();
if (!block)
continue;
ASSERT(block->isReachable);
for (unsigned phiIndex = block->phis.size(); phiIndex--;) {
Node* phi = block->phis[phiIndex];
for (unsigned childIdx = 0; childIdx < AdjacencyList::Size; ++childIdx) {
if (!phi->children.child(childIdx))
break;
phi->variableAccessData()->unify(
phi->children.child(childIdx)->variableAccessData());
}
}
}
// Ensure that all predictions are fixed up based on the unification.
for (unsigned i = 0; i < m_graph.m_variableAccessData.size(); ++i) {
VariableAccessData* data = &m_graph.m_variableAccessData[i];
data->find()->predict(data->nonUnifiedPrediction());
data->find()->mergeIsCaptured(data->isCaptured());
data->find()->mergeStructureCheckHoistingFailed(data->structureCheckHoistingFailed());
data->find()->mergeShouldNeverUnbox(data->shouldNeverUnbox());
data->find()->mergeIsLoadedFrom(data->isLoadedFrom());
}
m_graph.m_unificationState = GloballyUnified;
return true;
}
void doRoundOfDoubleVoting()
{
#if DFG_ENABLE(DEBUG_PROPAGATION_VERBOSE)
dataLog("Voting on double uses of locals [%u]\n", m_count);
#endif
for (unsigned i = 0; i < m_graph.m_variableAccessData.size(); ++i)
m_graph.m_variableAccessData[i].find()->clearVotes();
for (m_compileIndex = 0; m_compileIndex < m_graph.size(); ++m_compileIndex) {
Node& node = m_graph[m_compileIndex];
switch (node.op()) {
case ValueAdd:
case ArithAdd:
case ArithSub: {
SpeculatedType left = m_graph[node.child1()].prediction();
SpeculatedType right = m_graph[node.child2()].prediction();
DoubleBallot ballot;
if (isNumberSpeculation(left) && isNumberSpeculation(right)
&& !m_graph.addShouldSpeculateInteger(node))
ballot = VoteDouble;
else
ballot = VoteValue;
m_graph.vote(node.child1(), ballot);
m_graph.vote(node.child2(), ballot);
break;
}
case ArithMul: {
SpeculatedType left = m_graph[node.child1()].prediction();
SpeculatedType right = m_graph[node.child2()].prediction();
DoubleBallot ballot;
if (isNumberSpeculation(left) && isNumberSpeculation(right)
&& !m_graph.mulShouldSpeculateInteger(node))
ballot = VoteDouble;
else
ballot = VoteValue;
m_graph.vote(node.child1(), ballot);
m_graph.vote(node.child2(), ballot);
break;
}
case ArithMin:
case ArithMax:
case ArithMod:
case ArithDiv: {
SpeculatedType left = m_graph[node.child1()].prediction();
SpeculatedType right = m_graph[node.child2()].prediction();
DoubleBallot ballot;
if (isNumberSpeculation(left) && isNumberSpeculation(right)
&& !(Node::shouldSpeculateInteger(m_graph[node.child1()], m_graph[node.child1()])
&& node.canSpeculateInteger()))
ballot = VoteDouble;
else
ballot = VoteValue;
m_graph.vote(node.child1(), ballot);
m_graph.vote(node.child2(), ballot);
break;
}
case ArithAbs:
DoubleBallot ballot;
if (!(m_graph[node.child1()].shouldSpeculateInteger()
&& node.canSpeculateInteger()))
ballot = VoteDouble;
else
ballot = VoteValue;
m_graph.vote(node.child1(), ballot);
break;
case ArithSqrt:
m_graph.vote(node.child1(), VoteDouble);
break;
case SetLocal: {
SpeculatedType prediction = m_graph[node.child1()].prediction();
if (isDoubleSpeculation(prediction))
node.variableAccessData()->vote(VoteDouble);
else if (!isNumberSpeculation(prediction) || isInt32Speculation(prediction))
node.variableAccessData()->vote(VoteValue);
break;
}
default:
m_graph.vote(node, VoteValue);
break;
}
}
for (unsigned i = 0; i < m_graph.m_variableAccessData.size(); ++i) {
VariableAccessData* variableAccessData = &m_graph.m_variableAccessData[i];
if (!variableAccessData->isRoot())
continue;
if (operandIsArgument(variableAccessData->local())
|| variableAccessData->isCaptured())
continue;
m_changed |= variableAccessData->tallyVotesForShouldUseDoubleFormat();
}
for (unsigned i = 0; i < m_graph.m_argumentPositions.size(); ++i)
m_changed |= m_graph.m_argumentPositions[i].mergeArgumentAwareness();
for (unsigned i = 0; i < m_graph.m_variableAccessData.size(); ++i) {
VariableAccessData* variableAccessData = &m_graph.m_variableAccessData[i];
if (!variableAccessData->isRoot())
continue;
if (operandIsArgument(variableAccessData->local())
|| variableAccessData->isCaptured())
continue;
m_changed |= variableAccessData->makePredictionForDoubleFormat();
}
}
bool run()
{
for (unsigned i = m_graph.m_variableAccessData.size(); i--;) {
VariableAccessData* variable = &m_graph.m_variableAccessData[i];
if (!variable->isRoot())
continue;
variable->clearVotes();
}
// Identify the set of variables that are always subject to the same structure
// checks. For now, only consider monomorphic structure checks (one structure).
for (BlockIndex blockIndex = 0; blockIndex < m_graph.m_blocks.size(); ++blockIndex) {
BasicBlock* block = m_graph.m_blocks[blockIndex].get();
if (!block)
continue;
for (unsigned indexInBlock = 0; indexInBlock < block->size(); ++indexInBlock) {
NodeIndex nodeIndex = block->at(indexInBlock);
Node& node = m_graph[nodeIndex];
if (!node.shouldGenerate())
continue;
switch (node.op()) {
case CheckStructure: {
Node& child = m_graph[node.child1()];
if (child.op() != GetLocal)
break;
VariableAccessData* variable = child.variableAccessData();
variable->vote(VoteStructureCheck);
if (variable->isCaptured() || variable->structureCheckHoistingFailed())
break;
if (!isCellSpeculation(variable->prediction()))
break;
noticeStructureCheck(variable, node.structureSet());
break;
}
case ForwardCheckStructure:
case ForwardStructureTransitionWatchpoint:
// We currently rely on the fact that we're the only ones who would
// insert this node.
ASSERT_NOT_REACHED();
break;
case GetByOffset:
case PutByOffset:
case PutStructure:
case StructureTransitionWatchpoint:
case AllocatePropertyStorage:
case ReallocatePropertyStorage:
case GetPropertyStorage:
case GetByVal:
case PutByVal:
case PutByValAlias:
case GetArrayLength:
case CheckArray:
case GetIndexedPropertyStorage:
case Phantom:
// Don't count these uses.
break;
default:
m_graph.vote(node, VoteOther);
break;
}
}
}
// Disable structure hoisting on variables that appear to mostly be used in
// contexts where it doesn't make sense.
for (unsigned i = m_graph.m_variableAccessData.size(); i--;) {
VariableAccessData* variable = &m_graph.m_variableAccessData[i];
if (!variable->isRoot())
continue;
if (variable->voteRatio() >= Options::structureCheckVoteRatioForHoisting())
continue;
HashMap<VariableAccessData*, CheckData>::iterator iter = m_map.find(variable);
if (iter == m_map.end())
continue;
#if DFG_ENABLE(DEBUG_PROPAGATION_VERBOSE)
dataLog("Zeroing the structure to hoist for %s because the ratio is %lf.\n",
m_graph.nameOfVariableAccessData(variable), variable->voteRatio());
#endif
iter->second.m_structure = 0;
}
// Identify the set of variables that are live across a structure clobber.
Operands<VariableAccessData*> live(
m_graph.m_blocks[0]->variablesAtTail.numberOfArguments(),
m_graph.m_blocks[0]->variablesAtTail.numberOfLocals());
for (BlockIndex blockIndex = 0; blockIndex < m_graph.m_blocks.size(); ++blockIndex) {
BasicBlock* block = m_graph.m_blocks[blockIndex].get();
if (!block)
continue;
ASSERT(live.numberOfArguments() == block->variablesAtTail.numberOfArguments());
ASSERT(live.numberOfLocals() == block->variablesAtTail.numberOfLocals());
for (unsigned i = live.size(); i--;) {
NodeIndex indexAtTail = block->variablesAtTail[i];
VariableAccessData* variable;
if (indexAtTail == NoNode)
variable = 0;
else
variable = m_graph[indexAtTail].variableAccessData();
live[i] = variable;
}
for (unsigned indexInBlock = block->size(); indexInBlock--;) {
NodeIndex nodeIndex = block->at(indexInBlock);
Node& node = m_graph[nodeIndex];
if (!node.shouldGenerate())
continue;
switch (node.op()) {
case GetLocal:
case Flush:
// This is a birth.
live.operand(node.local()) = node.variableAccessData();
break;
case SetLocal:
case SetArgument:
ASSERT(live.operand(node.local())); // Must be live.
ASSERT(live.operand(node.local()) == node.variableAccessData()); // Must have the variable we expected.
// This is a death.
live.operand(node.local()) = 0;
break;
// Use the CFA's notion of what clobbers the world.
case ValueAdd:
if (m_graph.addShouldSpeculateInteger(node))
break;
if (Node::shouldSpeculateNumber(m_graph[node.child1()], m_graph[node.child2()]))
break;
clobber(live);
break;
case CompareLess:
case CompareLessEq:
case CompareGreater:
case CompareGreaterEq:
case CompareEq: {
Node& left = m_graph[node.child1()];
Node& right = m_graph[node.child2()];
if (Node::shouldSpeculateInteger(left, right))
break;
if (Node::shouldSpeculateNumber(left, right))
break;
if (node.op() == CompareEq) {
if ((m_graph.isConstant(node.child1().index())
&& m_graph.valueOfJSConstant(node.child1().index()).isNull())
|| (m_graph.isConstant(node.child2().index())
&& m_graph.valueOfJSConstant(node.child2().index()).isNull()))
break;
if (Node::shouldSpeculateFinalObject(left, right))
break;
if (Node::shouldSpeculateArray(left, right))
break;
if (left.shouldSpeculateFinalObject() && right.shouldSpeculateFinalObjectOrOther())
break;
if (right.shouldSpeculateFinalObject() && left.shouldSpeculateFinalObjectOrOther())
break;
if (left.shouldSpeculateArray() && right.shouldSpeculateArrayOrOther())
break;
if (right.shouldSpeculateArray() && left.shouldSpeculateArrayOrOther())
break;
}
clobber(live);
break;
}
case GetByVal:
case PutByVal:
case PutByValAlias:
if (m_graph.byValIsPure(node))
break;
clobber(live);
break;
case GetMyArgumentsLengthSafe:
case GetMyArgumentByValSafe:
case GetById:
case GetByIdFlush:
case PutStructure:
case PhantomPutStructure:
case PutById:
case PutByIdDirect:
case Call:
case Construct:
case Resolve:
case ResolveBase:
case ResolveBaseStrictPut:
case ResolveGlobal:
clobber(live);
break;
default:
ASSERT(node.op() != Phi);
break;
}
}
}
bool changed = false;
#if DFG_ENABLE(DEBUG_PROPAGATION_VERBOSE)
for (HashMap<VariableAccessData*, CheckData>::iterator it = m_map.begin();
it != m_map.end(); ++it) {
if (!it->second.m_structure) {
dataLog("Not hoisting checks for %s because of heuristics.\n", m_graph.nameOfVariableAccessData(it->first));
continue;
}
if (it->second.m_isClobbered && !it->second.m_structure->transitionWatchpointSetIsStillValid()) {
dataLog("Not hoisting checks for %s because the structure is clobbered and has an invalid watchpoint set.\n", m_graph.nameOfVariableAccessData(it->first));
continue;
}
dataLog("Hoisting checks for %s\n", m_graph.nameOfVariableAccessData(it->first));
}
#endif // DFG_ENABLE(DEBUG_PROPAGATION_VERBOSE)
// Make changes:
// 1) If a variable's live range does not span a clobber, then inject structure
// checks before the SetLocal.
// 2) If a variable's live range spans a clobber but is watchpointable, then
// inject structure checks before the SetLocal and replace all other structure
// checks on that variable with structure transition watchpoints.
InsertionSet<NodeIndex> insertionSet;
for (BlockIndex blockIndex = 0; blockIndex < m_graph.m_blocks.size(); ++blockIndex) {
BasicBlock* block = m_graph.m_blocks[blockIndex].get();
if (!block)
continue;
for (unsigned indexInBlock = 0; indexInBlock < block->size(); ++indexInBlock) {
NodeIndex nodeIndex = block->at(indexInBlock);
Node& node = m_graph[nodeIndex];
// Be careful not to use 'node' after appending to the graph. In those switch
// cases where we need to append, we first carefully extract everything we need
// from the node, before doing any appending.
if (!node.shouldGenerate())
continue;
switch (node.op()) {
case SetArgument: {
ASSERT(!blockIndex);
// Insert a GetLocal and a CheckStructure immediately following this
// SetArgument, if the variable was a candidate for structure hoisting.
// If the basic block previously only had the SetArgument as its
// variable-at-tail, then replace it with this GetLocal.
VariableAccessData* variable = node.variableAccessData();
HashMap<VariableAccessData*, CheckData>::iterator iter = m_map.find(variable);
if (iter == m_map.end())
break;
if (!iter->second.m_structure)
break;
if (iter->second.m_isClobbered && !iter->second.m_structure->transitionWatchpointSetIsStillValid())
break;
node.ref();
CodeOrigin codeOrigin = node.codeOrigin;
Node getLocal(GetLocal, codeOrigin, OpInfo(variable), nodeIndex);
getLocal.predict(variable->prediction());
getLocal.ref();
NodeIndex getLocalIndex = m_graph.size();
m_graph.append(getLocal);
insertionSet.append(indexInBlock + 1, getLocalIndex);
Node checkStructure(CheckStructure, codeOrigin, OpInfo(m_graph.addStructureSet(iter->second.m_structure)), getLocalIndex);
checkStructure.ref();
NodeIndex checkStructureIndex = m_graph.size();
m_graph.append(checkStructure);
insertionSet.append(indexInBlock + 1, checkStructureIndex);
if (block->variablesAtTail.operand(variable->local()) == nodeIndex)
block->variablesAtTail.operand(variable->local()) = getLocalIndex;
m_graph.substituteGetLocal(*block, indexInBlock, variable, getLocalIndex);
changed = true;
break;
}
case SetLocal: {
VariableAccessData* variable = node.variableAccessData();
HashMap<VariableAccessData*, CheckData>::iterator iter = m_map.find(variable);
if (iter == m_map.end())
break;
if (!iter->second.m_structure)
break;
if (iter->second.m_isClobbered && !iter->second.m_structure->transitionWatchpointSetIsStillValid())
break;
// First insert a dead SetLocal to tell OSR that the child's value should
// be dropped into this bytecode variable if the CheckStructure decides
// to exit.
CodeOrigin codeOrigin = node.codeOrigin;
NodeIndex child1 = node.child1().index();
Node setLocal(SetLocal, codeOrigin, OpInfo(variable), child1);
NodeIndex setLocalIndex = m_graph.size();
m_graph.append(setLocal);
insertionSet.append(indexInBlock, setLocalIndex);
m_graph[child1].ref();
// Use a ForwardCheckStructure to indicate that we should exit to the
// next bytecode instruction rather than reexecuting the current one.
Node checkStructure(ForwardCheckStructure, codeOrigin, OpInfo(m_graph.addStructureSet(iter->second.m_structure)), child1);
checkStructure.ref();
NodeIndex checkStructureIndex = m_graph.size();
m_graph.append(checkStructure);
insertionSet.append(indexInBlock, checkStructureIndex);
changed = true;
break;
}
case CheckStructure: {
Node& child = m_graph[node.child1()];
if (child.op() != GetLocal)
break;
HashMap<VariableAccessData*, CheckData>::iterator iter = m_map.find(child.variableAccessData());
if (iter == m_map.end())
break;
if (!iter->second.m_structure)
break;
if (!iter->second.m_isClobbered) {
node.setOpAndDefaultFlags(Phantom);
ASSERT(node.refCount() == 1);
break;
}
if (!iter->second.m_structure->transitionWatchpointSetIsStillValid())
break;
ASSERT(iter->second.m_structure == node.structureSet().singletonStructure());
node.convertToStructureTransitionWatchpoint();
changed = true;
break;
}
default:
break;
}
}
insertionSet.execute(*block);
}
return changed;
}
bool run()
{
RELEASE_ASSERT(m_graph.m_form == ThreadedCPS);
if (dumpGraph) {
dataLog("Graph dump at top of SSA conversion:\n");
m_graph.dump();
}
// Eliminate all duplicate or self-pointing Phi edges. This means that
// we transform:
//
// p: Phi(@n1, @n2, @n3)
//
// into:
//
// p: Phi(@x)
//
// if each @ni in {@n1, @n2, @n3} is either equal to @p to is equal
// to @x, for exactly one other @x. Additionally, trivial Phis (i.e.
// p: Phi(@x)) are forwarded, so that if have an edge to such @p, we
// replace it with @x. This loop does this for Phis only; later we do
// such forwarding for Phi references found in other nodes.
//
// See Aycock and Horspool in CC'00 for a better description of what
// we're doing here.
do {
m_changed = false;
for (BlockIndex blockIndex = m_graph.numBlocks(); blockIndex--;) {
BasicBlock* block = m_graph.block(blockIndex);
if (!block)
continue;
for (unsigned phiIndex = block->phis.size(); phiIndex--;) {
Node* phi = block->phis[phiIndex];
if (phi->variableAccessData()->isCaptured())
continue;
forwardPhiChildren(phi);
deduplicateChildren(phi);
}
}
} while (m_changed);
// For each basic block, for each local live at the head of that block,
// figure out what node we should be referring to instead of that local.
// If it turns out to be a non-trivial Phi, make sure that we create an
// SSA Phi and Upsilons in predecessor blocks. We reuse
// BasicBlock::variablesAtHead for tracking which nodes to refer to.
Operands<bool> nonTrivialPhis(OperandsLike, m_graph.block(0)->variablesAtHead);
for (BlockIndex blockIndex = m_graph.numBlocks(); blockIndex--;) {
BasicBlock* block = m_graph.block(blockIndex);
if (!block)
continue;
nonTrivialPhis.fill(false);
for (unsigned i = block->phis.size(); i--;) {
Node* phi = block->phis[i];
if (!phi->children.justOneChild())
nonTrivialPhis.operand(phi->local()) = true;
}
for (unsigned i = block->variablesAtHead.size(); i--;) {
Node* node = block->variablesAtHead[i];
if (!node)
continue;
if (verbose)
dataLog("At block #", blockIndex, " for operand r", block->variablesAtHead.operandForIndex(i), " have node ", node, "\n");
VariableAccessData* variable = node->variableAccessData();
if (variable->isCaptured()) {
// Poison this entry in variablesAtHead because we don't
// want anyone to try to refer to it, if the variable is
// captured.
block->variablesAtHead[i] = 0;
continue;
}
switch (node->op()) {
case Phi:
case SetArgument:
break;
case Flush:
case GetLocal:
case PhantomLocal:
node = node->child1().node();
break;
default:
RELEASE_ASSERT_NOT_REACHED();
}
RELEASE_ASSERT(node->op() == Phi || node->op() == SetArgument);
bool isFlushed = !!(node->flags() & NodeIsFlushed);
if (node->op() == Phi) {
if (!nonTrivialPhis.operand(node->local())) {
Edge edge = node->children.justOneChild();
ASSERT(edge);
if (verbose)
dataLog(" One child: ", edge, ", ", RawPointer(edge.node()), "\n");
node = edge.node(); // It's something from a different basic block.
} else {
if (verbose)
dataLog(" Non-trivial.\n");
// It's a non-trivial Phi.
FlushFormat format = variable->flushFormat();
NodeFlags result = resultFor(format);
UseKind useKind = useKindFor(format);
node = m_insertionSet.insertNode(0, SpecNone, Phi, NodeOrigin());
if (verbose)
dataLog(" Inserted new node: ", node, "\n");
node->mergeFlags(result);
RELEASE_ASSERT((node->flags() & NodeResultMask) == result);
for (unsigned j = block->predecessors.size(); j--;) {
BasicBlock* predecessor = block->predecessors[j];
predecessor->appendNonTerminal(
m_graph, SpecNone, Upsilon, predecessor->last()->origin,
OpInfo(node), Edge(predecessor->variablesAtTail[i], useKind));
}
if (isFlushed) {
// Do nothing. For multiple reasons.
// Reason #1: If the local is flushed then we don't need to bother
// with a MovHint since every path to this point in the code will
// have flushed the bytecode variable using a SetLocal and hence
// the Availability::flushedAt() will agree, and that will be
// sufficient for figuring out how to recover the variable's value.
// Reason #2: If we had inserted a MovHint and the Phi function had
// died (because the only user of the value was the "flush" - i.e.
// some asynchronous runtime thingy) then the MovHint would turn
// into a ZombieHint, which would fool us into thinking that the
// variable is dead.
// Reason #3: If we had inserted a MovHint then even if the Phi
// stayed alive, we would still end up generating inefficient code
// since we would be telling the OSR exit compiler to use some SSA
// value for the bytecode variable rather than just telling it that
// the value was already on the stack.
} else {
m_insertionSet.insertNode(
0, SpecNone, MovHint, NodeOrigin(),
OpInfo(variable->local().offset()), Edge(node));
}
}
}
block->variablesAtHead[i] = node;
}
m_insertionSet.execute(block);
}
if (verbose) {
dataLog("Variables at head after SSA Phi insertion:\n");
for (BlockIndex blockIndex = m_graph.numBlocks(); blockIndex--;) {
BasicBlock* block = m_graph.block(blockIndex);
if (!block)
continue;
dataLog(" ", *block, ": ", block->variablesAtHead, "\n");
}
}
// At this point variablesAtHead in each block refers to either:
//
// 1) A new SSA phi in the current block.
// 2) A SetArgument, which will soon get converted into a GetArgument.
// 3) An old CPS phi in a different block.
//
// We don't have to do anything for (1) and (2), but we do need to
// do a replacement for (3).
// Clear all replacements, since other phases may have used them.
m_graph.clearReplacements();
if (dumpGraph) {
dataLog("Graph just before identifying replacements:\n");
m_graph.dump();
}
// For all of the old CPS Phis, figure out what they correspond to in SSA.
for (BlockIndex blockIndex = m_graph.numBlocks(); blockIndex--;) {
BasicBlock* block = m_graph.block(blockIndex);
if (!block)
continue;
if (verbose)
dataLog("Dealing with block #", blockIndex, "\n");
for (unsigned phiIndex = block->phis.size(); phiIndex--;) {
Node* phi = block->phis[phiIndex];
if (verbose) {
dataLog(
"Considering ", phi, " (", RawPointer(phi), "), for r",
phi->local(), ", and its replacement in ", *block, ", ",
block->variablesAtHead.operand(phi->local()), "\n");
}
ASSERT(phi != block->variablesAtHead.operand(phi->local()));
phi->misc.replacement = block->variablesAtHead.operand(phi->local());
}
}
// Now make sure that all variablesAtHead in each block points to the
// canonical SSA value. Prior to this, variablesAtHead[local] may point to
// an old CPS Phi in a different block.
for (BlockIndex blockIndex = m_graph.numBlocks(); blockIndex--;) {
BasicBlock* block = m_graph.block(blockIndex);
if (!block)
continue;
for (size_t i = block->variablesAtHead.size(); i--;) {
Node* node = block->variablesAtHead[i];
if (!node)
continue;
while (node->misc.replacement) {
ASSERT(node != node->misc.replacement);
node = node->misc.replacement;
}
block->variablesAtHead[i] = node;
}
}
if (verbose) {
dataLog("Variables at head after convergence:\n");
for (BlockIndex blockIndex = m_graph.numBlocks(); blockIndex--;) {
BasicBlock* block = m_graph.block(blockIndex);
if (!block)
continue;
dataLog(" ", *block, ": ", block->variablesAtHead, "\n");
}
}
// Convert operations over locals into operations over SSA nodes.
// - GetLocal over captured variables lose their phis.
// - GetLocal over uncaptured variables die and get replaced with references
// to the node specified by variablesAtHead.
// - SetLocal gets NodeMustGenerate if it's flushed, or turns into a
// Check otherwise.
// - Flush loses its children and turns into a Phantom.
// - PhantomLocal becomes Phantom, and its child is whatever is specified
// by variablesAtHead.
// - SetArgument turns into GetArgument unless it's a captured variable.
// - Upsilons get their children fixed to refer to the true value of that local
// at the end of the block. Prior to this loop, Upsilons will refer to
// variableAtTail[operand], which may be any of Flush, PhantomLocal, GetLocal,
// SetLocal, SetArgument, or Phi. We accomplish this by setting the
// replacement pointers of all of those nodes to refer to either
// variablesAtHead[operand], or the child of the SetLocal.
for (BlockIndex blockIndex = m_graph.numBlocks(); blockIndex--;) {
BasicBlock* block = m_graph.block(blockIndex);
if (!block)
continue;
for (unsigned phiIndex = block->phis.size(); phiIndex--;) {
block->phis[phiIndex]->misc.replacement =
block->variablesAtHead.operand(block->phis[phiIndex]->local());
}
for (unsigned nodeIndex = block->size(); nodeIndex--;)
ASSERT(!block->at(nodeIndex)->misc.replacement);
for (unsigned nodeIndex = 0; nodeIndex < block->size(); ++nodeIndex) {
Node* node = block->at(nodeIndex);
m_graph.performSubstitution(node);
switch (node->op()) {
case SetLocal: {
VariableAccessData* variable = node->variableAccessData();
if (variable->isCaptured() || !!(node->flags() & NodeIsFlushed))
node->mergeFlags(NodeMustGenerate);
else
node->setOpAndDefaultFlags(Check);
node->misc.replacement = node->child1().node(); // Only for Upsilons.
break;
}
case GetLocal: {
// It seems tempting to just do forwardPhi(GetLocal), except that we
// could have created a new (SSA) Phi, and the GetLocal could still be
// referring to an old (CPS) Phi. Uses variablesAtHead to tell us what
// to refer to.
node->children.reset();
VariableAccessData* variable = node->variableAccessData();
if (variable->isCaptured())
break;
node->convertToPhantom();
node->misc.replacement = block->variablesAtHead.operand(variable->local());
break;
}
case Flush: {
node->children.reset();
node->convertToPhantom();
// This is only for Upsilons. An Upsilon will only refer to a Flush if
// there were no SetLocals or GetLocals in the block.
node->misc.replacement = block->variablesAtHead.operand(node->local());
break;
}
case PhantomLocal: {
VariableAccessData* variable = node->variableAccessData();
if (variable->isCaptured())
break;
node->child1().setNode(block->variablesAtHead.operand(variable->local()));
node->convertToPhantom();
// This is only for Upsilons. An Upsilon will only refer to a
// PhantomLocal if there were no SetLocals or GetLocals in the block.
node->misc.replacement = block->variablesAtHead.operand(variable->local());
break;
}
case SetArgument: {
VariableAccessData* variable = node->variableAccessData();
if (variable->isCaptured())
break;
node->setOpAndDefaultFlags(GetArgument);
node->mergeFlags(resultFor(node->variableAccessData()->flushFormat()));
break;
}
default:
break;
}
}
}
// Free all CPS phis and reset variables vectors.
for (BlockIndex blockIndex = m_graph.numBlocks(); blockIndex--;) {
BasicBlock* block = m_graph.block(blockIndex);
if (!block)
continue;
for (unsigned phiIndex = block->phis.size(); phiIndex--;)
m_graph.m_allocator.free(block->phis[phiIndex]);
block->phis.clear();
block->variablesAtHead.clear();
block->variablesAtTail.clear();
block->valuesAtHead.clear();
block->valuesAtHead.clear();
block->ssa = adoptPtr(new BasicBlock::SSAData(block));
}
m_graph.m_arguments.clear();
m_graph.m_form = SSA;
return true;
}
bool run()
{
RELEASE_ASSERT(m_graph.m_form == ThreadedCPS);
m_graph.clearReplacements();
m_graph.m_dominators.computeIfNecessary(m_graph);
if (verbose) {
dataLog("Graph before SSA transformation:\n");
m_graph.dump();
}
// Create a SSACalculator::Variable for every root VariableAccessData.
for (VariableAccessData& variable : m_graph.m_variableAccessData) {
if (!variable.isRoot() || variable.isCaptured())
continue;
SSACalculator::Variable* ssaVariable = m_calculator.newVariable();
ASSERT(ssaVariable->index() == m_variableForSSAIndex.size());
m_variableForSSAIndex.append(&variable);
m_ssaVariableForVariable.add(&variable, ssaVariable);
}
// Find all SetLocals and create Defs for them. We handle SetArgument by creating a
// GetLocal, and recording the flush format.
for (BlockIndex blockIndex = m_graph.numBlocks(); blockIndex--;) {
BasicBlock* block = m_graph.block(blockIndex);
if (!block)
continue;
// Must process the block in forward direction because we want to see the last
// assignment for every local.
for (unsigned nodeIndex = 0; nodeIndex < block->size(); ++nodeIndex) {
Node* node = block->at(nodeIndex);
if (node->op() != SetLocal && node->op() != SetArgument)
continue;
VariableAccessData* variable = node->variableAccessData();
if (variable->isCaptured())
continue;
Node* childNode;
if (node->op() == SetLocal)
childNode = node->child1().node();
else {
ASSERT(node->op() == SetArgument);
childNode = m_insertionSet.insertNode(
nodeIndex, node->variableAccessData()->prediction(),
GetStack, node->origin,
OpInfo(m_graph.m_stackAccessData.add(variable->local(), variable->flushFormat())));
if (!ASSERT_DISABLED)
m_argumentGetters.add(childNode);
m_argumentMapping.add(node, childNode);
}
m_calculator.newDef(
m_ssaVariableForVariable.get(variable), block, childNode);
}
m_insertionSet.execute(block);
}
// Decide where Phis are to be inserted. This creates the Phi's but doesn't insert them
// yet. We will later know where to insert them because SSACalculator is such a bro.
m_calculator.computePhis(
[&] (SSACalculator::Variable* ssaVariable, BasicBlock* block) -> Node* {
VariableAccessData* variable = m_variableForSSAIndex[ssaVariable->index()];
// Prune by liveness. This doesn't buy us much other than compile times.
Node* headNode = block->variablesAtHead.operand(variable->local());
if (!headNode)
return nullptr;
// There is the possibiltiy of "rebirths". The SSA calculator will already prune
// rebirths for the same VariableAccessData. But it will not be able to prune
// rebirths that arose from the same local variable number but a different
// VariableAccessData. We do that pruning here.
//
// Here's an example of a rebirth that this would catch:
//
// var x;
// if (foo) {
// if (bar) {
// x = 42;
// } else {
// x = 43;
// }
// print(x);
// x = 44;
// } else {
// x = 45;
// }
// print(x); // Without this check, we'd have a Phi for x = 42|43 here.
//
// FIXME: Consider feeding local variable numbers, not VariableAccessData*'s, as
// the "variables" for SSACalculator. That would allow us to eliminate this
// special case.
// https://bugs.webkit.org/show_bug.cgi?id=136641
if (headNode->variableAccessData() != variable)
return nullptr;
Node* phiNode = m_graph.addNode(
variable->prediction(), Phi, NodeOrigin());
FlushFormat format = variable->flushFormat();
NodeFlags result = resultFor(format);
phiNode->mergeFlags(result);
return phiNode;
});
if (verbose) {
dataLog("Computed Phis, about to transform the graph.\n");
dataLog("\n");
dataLog("Graph:\n");
m_graph.dump();
dataLog("\n");
dataLog("Mappings:\n");
for (unsigned i = 0; i < m_variableForSSAIndex.size(); ++i)
dataLog(" ", i, ": ", VariableAccessDataDump(m_graph, m_variableForSSAIndex[i]), "\n");
dataLog("\n");
dataLog("SSA calculator: ", m_calculator, "\n");
}
// Do the bulk of the SSA conversion. For each block, this tracks the operand->Node
// mapping based on a combination of what the SSACalculator tells us, and us walking over
// the block in forward order. We use our own data structure, valueForOperand, for
// determining the local mapping, but we rely on SSACalculator for the non-local mapping.
//
// This does three things at once:
//
// - Inserts the Phis in all of the places where they need to go. We've already created
// them and they are accounted for in the SSACalculator's data structures, but we
// haven't inserted them yet, mostly because we want to insert all of a block's Phis in
// one go to amortize the cost of node insertion.
//
// - Create and insert Upsilons.
//
// - Convert all of the preexisting SSA nodes (other than the old CPS Phi nodes) into SSA
// form by replacing as follows:
//
// - MovHint has KillLocal prepended to it.
//
// - GetLocal over captured variables lose their phis and become GetStack.
//
// - GetLocal over uncaptured variables die and get replaced with references to the node
// specified by valueForOperand.
//
// - SetLocal turns into PutStack if it's flushed, or turns into a Check otherwise.
//
// - Flush loses its children and turns into a Phantom.
//
// - PhantomLocal becomes Phantom, and its child is whatever is specified by
// valueForOperand.
//
// - SetArgument is removed. Note that GetStack nodes have already been inserted.
Operands<Node*> valueForOperand(OperandsLike, m_graph.block(0)->variablesAtHead);
for (BasicBlock* block : m_graph.blocksInPreOrder()) {
valueForOperand.clear();
// CPS will claim that the root block has all arguments live. But we have already done
// the first step of SSA conversion: argument locals are no longer live at head;
// instead we have GetStack nodes for extracting the values of arguments. So, we
// skip the at-head available value calculation for the root block.
if (block != m_graph.block(0)) {
for (size_t i = valueForOperand.size(); i--;) {
Node* nodeAtHead = block->variablesAtHead[i];
if (!nodeAtHead)
continue;
VariableAccessData* variable = nodeAtHead->variableAccessData();
if (variable->isCaptured())
continue;
if (verbose)
dataLog("Considering live variable ", VariableAccessDataDump(m_graph, variable), " at head of block ", *block, "\n");
SSACalculator::Variable* ssaVariable = m_ssaVariableForVariable.get(variable);
SSACalculator::Def* def = m_calculator.reachingDefAtHead(block, ssaVariable);
if (!def) {
// If we are required to insert a Phi, then we won't have a reaching def
// at head.
continue;
}
Node* node = def->value();
if (node->replacement) {
// This will occur when a SetLocal had a GetLocal as its source. The
// GetLocal would get replaced with an actual SSA value by the time we get
// here. Note that the SSA value with which the GetLocal got replaced
// would not in turn have a replacement.
node = node->replacement;
ASSERT(!node->replacement);
}
if (verbose)
dataLog("Mapping: ", VirtualRegister(valueForOperand.operandForIndex(i)), " -> ", node, "\n");
valueForOperand[i] = node;
}
}
// Insert Phis by asking the calculator what phis there are in this block. Also update
// valueForOperand with those Phis. For Phis associated with variables that are not
// flushed, we also insert a MovHint.
size_t phiInsertionPoint = 0;
for (SSACalculator::Def* phiDef : m_calculator.phisForBlock(block)) {
VariableAccessData* variable = m_variableForSSAIndex[phiDef->variable()->index()];
m_insertionSet.insert(phiInsertionPoint, phiDef->value());
valueForOperand.operand(variable->local()) = phiDef->value();
m_insertionSet.insertNode(
phiInsertionPoint, SpecNone, MovHint, NodeOrigin(),
OpInfo(variable->local().offset()), phiDef->value()->defaultEdge());
}
for (unsigned nodeIndex = 0; nodeIndex < block->size(); ++nodeIndex) {
Node* node = block->at(nodeIndex);
if (verbose) {
dataLog("Processing node ", node, ":\n");
m_graph.dump(WTF::dataFile(), " ", node);
}
m_graph.performSubstitution(node);
switch (node->op()) {
case MovHint: {
m_insertionSet.insertNode(
nodeIndex, SpecNone, KillStack, node->origin,
OpInfo(node->unlinkedLocal().offset()));
break;
}
case SetLocal: {
VariableAccessData* variable = node->variableAccessData();
if (variable->isCaptured() || !!(node->flags() & NodeIsFlushed)) {
node->convertToPutStack(
m_graph.m_stackAccessData.add(
variable->local(), variable->flushFormat()));
} else
node->setOpAndDefaultFlags(Check);
if (!variable->isCaptured()) {
if (verbose)
dataLog("Mapping: ", variable->local(), " -> ", node->child1().node(), "\n");
valueForOperand.operand(variable->local()) = node->child1().node();
}
break;
}
case GetStack: {
ASSERT(m_argumentGetters.contains(node));
valueForOperand.operand(node->stackAccessData()->local) = node;
break;
}
case GetLocal: {
VariableAccessData* variable = node->variableAccessData();
node->children.reset();
if (variable->isCaptured()) {
node->convertToGetStack(m_graph.m_stackAccessData.add(variable->local(), variable->flushFormat()));
break;
}
node->convertToPhantom();
if (verbose)
dataLog("Replacing node ", node, " with ", valueForOperand.operand(variable->local()), "\n");
node->replacement = valueForOperand.operand(variable->local());
break;
}
case Flush: {
node->children.reset();
node->convertToPhantom();
break;
}
case PhantomLocal: {
ASSERT(node->child1().useKind() == UntypedUse);
VariableAccessData* variable = node->variableAccessData();
if (variable->isCaptured()) {
// This is a fun case. We could have a captured variable that had some
// or all of its uses strength reduced to phantoms rather than flushes.
// SSA conversion will currently still treat it as flushed, in the sense
// that it will just keep the SetLocal. Therefore, there is nothing that
// needs to be done here: we don't need to also keep the source value
// alive. And even if we did want to keep the source value alive, we
// wouldn't be able to, because the variablesAtHead value for a captured
// local wouldn't have been computed by the Phi reduction algorithm
// above.
node->children.reset();
} else
node->child1() = valueForOperand.operand(variable->local())->defaultEdge();
node->convertToPhantom();
break;
}
case SetArgument: {
node->convertToPhantom();
break;
}
default:
break;
}
}
// We want to insert Upsilons just before the end of the block. On the surface this
// seems dangerous because the Upsilon will have a checking UseKind. But, we will not
// actually be performing the check at the point of the Upsilon; the check will
// already have been performed at the point where the original SetLocal was.
size_t upsilonInsertionPoint = block->size() - 1;
NodeOrigin upsilonOrigin = block->last()->origin;
for (unsigned successorIndex = block->numSuccessors(); successorIndex--;) {
BasicBlock* successorBlock = block->successor(successorIndex);
for (SSACalculator::Def* phiDef : m_calculator.phisForBlock(successorBlock)) {
Node* phiNode = phiDef->value();
SSACalculator::Variable* ssaVariable = phiDef->variable();
VariableAccessData* variable = m_variableForSSAIndex[ssaVariable->index()];
FlushFormat format = variable->flushFormat();
UseKind useKind = useKindFor(format);
m_insertionSet.insertNode(
upsilonInsertionPoint, SpecNone, Upsilon, upsilonOrigin,
OpInfo(phiNode), Edge(
valueForOperand.operand(variable->local()),
useKind));
}
}
m_insertionSet.execute(block);
}
// Free all CPS phis and reset variables vectors.
for (BlockIndex blockIndex = m_graph.numBlocks(); blockIndex--;) {
BasicBlock* block = m_graph.block(blockIndex);
if (!block)
continue;
for (unsigned phiIndex = block->phis.size(); phiIndex--;)
m_graph.m_allocator.free(block->phis[phiIndex]);
block->phis.clear();
block->variablesAtHead.clear();
block->variablesAtTail.clear();
block->valuesAtHead.clear();
block->valuesAtHead.clear();
block->ssa = std::make_unique<BasicBlock::SSAData>(block);
}
m_graph.m_argumentFormats.resize(m_graph.m_arguments.size());
for (unsigned i = m_graph.m_arguments.size(); i--;) {
FlushFormat format = FlushedJSValue;
Node* node = m_argumentMapping.get(m_graph.m_arguments[i]);
// m_argumentMapping.get could return null for a captured local. That's fine. We only
// track the argument loads of those arguments for which we speculate type. We don't
// speculate type for captured arguments.
if (node)
format = node->stackAccessData()->format;
m_graph.m_argumentFormats[i] = format;
m_graph.m_arguments[i] = node; // Record the load that loads the arguments for the benefit of exit profiling.
}
m_graph.m_form = SSA;
if (verbose) {
dataLog("Graph after SSA transformation:\n");
m_graph.dump();
}
return true;
}
