// A loop is about to be made reachable only through an OSR entry into one of
// its nested loops. Fix everything up.
bool
ValueNumberer::fixupOSROnlyLoop(MBasicBlock* block, MBasicBlock* backedge)
{
// Create an empty and unreachable(!) block which jumps to |block|. This
// allows |block| to remain marked as a loop header, so we don't have to
// worry about moving a different block into place as the new loop header,
// which is hard, especially if the OSR is into a nested loop. Doing all
// that would produce slightly more optimal code, but this is so
// extraordinarily rare that it isn't worth the complexity.
MBasicBlock* fake = MBasicBlock::New(graph_, block->info(), nullptr, MBasicBlock::NORMAL);
if (fake == nullptr)
return false;
graph_.insertBlockBefore(block, fake);
fake->setImmediateDominator(fake);
fake->addNumDominated(1);
fake->setDomIndex(fake->id());
fake->setUnreachable();
// Create zero-input phis to use as inputs for any phis in |block|.
// Again, this is a little odd, but it's the least-odd thing we can do
// without significant complexity.
for (MPhiIterator iter(block->phisBegin()), end(block->phisEnd()); iter != end; ++iter) {
MPhi* phi = *iter;
MPhi* fakePhi = MPhi::New(graph_.alloc(), phi->type());
fake->addPhi(fakePhi);
if (!phi->addInputSlow(fakePhi))
return false;
}
fake->end(MGoto::New(graph_.alloc(), block));
if (!block->addPredecessorWithoutPhis(fake))
return false;
// Restore |backedge| as |block|'s loop backedge.
block->clearLoopHeader();
block->setLoopHeader(backedge);
JitSpew(JitSpew_GVN, " Created fake block%u", fake->id());
hasOSRFixups_ = true;
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;
}
