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[Mem2Reg] Replaced loop with getSingleSuccessor.

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Thanks to the lack of critical edges in SIL, if a block B dominated by P
has a successor S which is not dominated by P, then B must have only a
single successor.  Used this fact to replace a loop over successors to a
call to getSinglePredecessor.

Also added an assertion that, in the notation above, B is dominated by
P.
This commit is contained in:
Nate Chandler
2021-11-02 09:50:43 -07:00
parent 2ad0eb7717
commit 09dde09a8d
1 changed files with 18 additions and 10 deletions
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28
lib/SILOptimizer/Transforms/SILMem2Reg.cpp
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@@ -1665,22 +1665,30 @@ void MemoryToRegisters::removeSingleBlockAllocation(AllocStackInst *asi) {
GraphNodeWorklist<SILBasicBlock *, 2> worklist;
worklist.initialize(parentBlock);
while (auto *block = worklist.pop()) {
assert(domInfo->dominates(parentBlock, block));
auto *terminator = block->getTerminator();
if (isa<UnreachableInst>(terminator)) {
endLexicalLifetimeBeforeInst(asi, /*beforeInstruction=*/terminator, ctx,
runningVals->value);
continue;
}
bool endedLifetime = false;
for (auto *successor : block->getSuccessorBlocks()) {
if (!domInfo->dominates(parentBlock, successor)) {
endLexicalLifetimeBeforeInst(asi, /*beforeInstruction=*/terminator,
ctx, runningVals->value);
endedLifetime = true;
break;
}
}
if (endedLifetime) {
SILBasicBlock *successor = nullptr;
// If any successor is not dominated by the parentBlock, then we must end
// the lifetime before that successor.
//
// Suppose that a successor is not dominated by parentBlock. Recall that
// block _is_ dominated by parentBlock. Thus that successor must have
// more than one predecessor: block, and at least one other. (Otherwise
// it would be dominated by parentBlock contrary to our assumption.)
// Recall that SIL does not allow critical edges. Therefore block has
// only a single successor.
//
// Use the above fact to only look for lack of domination of a successor
// if that successor is the single successor of block.
if ((successor = block->getSingleSuccessorBlock()) &&
(!domInfo->dominates(parentBlock, successor))) {
endLexicalLifetimeBeforeInst(asi, /*beforeInstruction=*/terminator, ctx,
runningVals->value);
continue;
}
for (auto *successor : block->getSuccessorBlocks()) {