void
ion::AssertGraphCoherency(MIRGraph &graph)
{
#ifdef DEBUG
// Assert successor and predecessor list coherency.
uint32_t count = 0;
for (MBasicBlockIterator block(graph.begin()); block != graph.end(); block++) {
count++;
for (size_t i = 0; i < block->numSuccessors(); i++)
JS_ASSERT(CheckSuccessorImpliesPredecessor(*block, block->getSuccessor(i)));
for (size_t i = 0; i < block->numPredecessors(); i++)
JS_ASSERT(CheckPredecessorImpliesSuccessor(*block, block->getPredecessor(i)));
for (MInstructionIterator ins = block->begin(); ins != block->end(); ins++) {
for (uint32_t i = 0; i < ins->numOperands(); i++)
JS_ASSERT(CheckMarkedAsUse(*ins, ins->getOperand(i)));
}
}
JS_ASSERT(graph.numBlocks() == count);
AssertReversePostOrder(graph);
#endif
}
// A bounds check is considered redundant if it's dominated by another bounds
// check with the same length and the indexes differ by only a constant amount.
// In this case we eliminate the redundant bounds check and update the other one
// to cover the ranges of both checks.
//
// Bounds checks are added to a hash map and since the hash function ignores
// differences in constant offset, this offers a fast way to find redundant
// checks.
bool
ion::EliminateRedundantBoundsChecks(MIRGraph &graph)
{
BoundsCheckMap checks;
if (!checks.init())
return false;
// Stack for pre-order CFG traversal.
Vector<MBasicBlock *, 1, IonAllocPolicy> worklist;
// The index of the current block in the CFG traversal.
size_t index = 0;
// Add all self-dominating blocks to the worklist.
// This includes all roots. Order does not matter.
for (MBasicBlockIterator i(graph.begin()); i != graph.end(); i++) {
MBasicBlock *block = *i;
if (block->immediateDominator() == block) {
if (!worklist.append(block))
return false;
}
}
// Starting from each self-dominating block, traverse the CFG in pre-order.
while (!worklist.empty()) {
MBasicBlock *block = worklist.popCopy();
// Add all immediate dominators to the front of the worklist.
for (size_t i = 0; i < block->numImmediatelyDominatedBlocks(); i++) {
if (!worklist.append(block->getImmediatelyDominatedBlock(i)))
return false;
}
for (MDefinitionIterator iter(block); iter; ) {
if (!iter->isBoundsCheck()) {
iter++;
continue;
}
MBoundsCheck *check = iter->toBoundsCheck();
// Replace all uses of the bounds check with the actual index.
// This is (a) necessary, because we can coalesce two different
// bounds checks and would otherwise use the wrong index and
// (b) helps register allocation. Note that this is safe since
// no other pass after bounds check elimination moves instructions.
check->replaceAllUsesWith(check->index());
if (!check->isMovable()) {
iter++;
continue;
}
MBoundsCheck *dominating = FindDominatingBoundsCheck(checks, check, index);
if (!dominating)
return false;
if (dominating == check) {
// We didn't find a dominating bounds check.
iter++;
continue;
}
bool eliminated = false;
if (!TryEliminateBoundsCheck(dominating, check, &eliminated))
return false;
if (eliminated)
iter = check->block()->discardDefAt(iter);
else
iter++;
}
index++;
}
JS_ASSERT(index == graph.numBlocks());
return true;
}
bool
ion::BuildDominatorTree(MIRGraph &graph)
{
ComputeImmediateDominators(graph);
// Traversing through the graph in post-order means that every use
// of a definition is visited before the def itself. Since a def
// dominates its uses, by the time we reach a particular
// block, we have processed all of its dominated children, so
// block->numDominated() is accurate.
for (PostorderIterator i(graph.poBegin()); i != graph.poEnd(); i++) {
MBasicBlock *child = *i;
MBasicBlock *parent = child->immediateDominator();
// If the block only self-dominates, it has no definite parent.
if (child == parent)
continue;
if (!parent->addImmediatelyDominatedBlock(child))
return false;
// An additional +1 for the child block.
parent->addNumDominated(child->numDominated() + 1);
}
#ifdef DEBUG
// If compiling with OSR, many blocks will self-dominate.
// Without OSR, there is only one root block which dominates all.
if (!graph.osrBlock())
JS_ASSERT(graph.begin()->numDominated() == graph.numBlocks() - 1);
#endif
// Now, iterate through the dominator tree and annotate every
// block with its index in the pre-order traversal of the
// dominator tree.
Vector<MBasicBlock *, 1, IonAllocPolicy> worklist;
// The index of the current block in the CFG traversal.
size_t index = 0;
// Add all self-dominating blocks to the worklist.
// This includes all roots. Order does not matter.
for (MBasicBlockIterator i(graph.begin()); i != graph.end(); i++) {
MBasicBlock *block = *i;
if (block->immediateDominator() == block) {
if (!worklist.append(block))
return false;
}
}
// Starting from each self-dominating block, traverse the CFG in pre-order.
while (!worklist.empty()) {
MBasicBlock *block = worklist.popCopy();
block->setDomIndex(index);
for (size_t i = 0; i < block->numImmediatelyDominatedBlocks(); i++) {
if (!worklist.append(block->getImmediatelyDominatedBlock(i)))
return false;
}
index++;
}
return true;
}
// Eliminate checks which are redundant given each other or other instructions.
//
// A type barrier is considered redundant if all missing types have been tested
// for by earlier control instructions.
//
// A bounds check is considered redundant if it's dominated by another bounds
// check with the same length and the indexes differ by only a constant amount.
// In this case we eliminate the redundant bounds check and update the other one
// to cover the ranges of both checks.
//
// Bounds checks are added to a hash map and since the hash function ignores
// differences in constant offset, this offers a fast way to find redundant
// checks.
bool
ion::EliminateRedundantChecks(MIRGraph &graph)
{
BoundsCheckMap checks;
if (!checks.init())
return false;
// Stack for pre-order CFG traversal.
Vector<MBasicBlock *, 1, IonAllocPolicy> worklist;
// The index of the current block in the CFG traversal.
size_t index = 0;
// Add all self-dominating blocks to the worklist.
// This includes all roots. Order does not matter.
for (MBasicBlockIterator i(graph.begin()); i != graph.end(); i++) {
MBasicBlock *block = *i;
if (block->immediateDominator() == block) {
if (!worklist.append(block))
return false;
}
}
// Starting from each self-dominating block, traverse the CFG in pre-order.
while (!worklist.empty()) {
MBasicBlock *block = worklist.popCopy();
// Add all immediate dominators to the front of the worklist.
for (size_t i = 0; i < block->numImmediatelyDominatedBlocks(); i++) {
if (!worklist.append(block->getImmediatelyDominatedBlock(i)))
return false;
}
for (MDefinitionIterator iter(block); iter; ) {
bool eliminated = false;
if (iter->isBoundsCheck()) {
if (!TryEliminateBoundsCheck(checks, index, iter->toBoundsCheck(), &eliminated))
return false;
} else if (iter->isTypeBarrier()) {
if (!TryEliminateTypeBarrier(iter->toTypeBarrier(), &eliminated))
return false;
} else if (iter->isConvertElementsToDoubles()) {
// Now that code motion passes have finished, replace any
// ConvertElementsToDoubles with the actual elements.
MConvertElementsToDoubles *ins = iter->toConvertElementsToDoubles();
ins->replaceAllUsesWith(ins->elements());
}
if (eliminated)
iter = block->discardDefAt(iter);
else
iter++;
}
index++;
}
JS_ASSERT(index == graph.numBlocks());
return true;
}