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Fix for PR3944: make mem2reg O(N) instead of O(N^2) in the number of 

incoming edges for a block with many predecessors.

llvm-svn: 69312
This commit is contained in:
Eli Friedman 2009-04-16 21:40:28 +00:00
parent 72dc8452a3
commit 929207fd1d
1 changed files with 11 additions and 19 deletions
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30
llvm/lib/Transforms/Utils/PromoteMemoryToRegister.cpp
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@ -890,22 +890,9 @@ NextIteration:
// If we are inserting any phi nodes into this BB, they will already be in the // If we are inserting any phi nodes into this BB, they will already be in the
// block. // block.
if (PHINode *APN = dyn_cast<PHINode>(BB->begin())) { if (PHINode *APN = dyn_cast<PHINode>(BB->begin())) {
// Pred may have multiple edges to BB. If so, we want to add N incoming
// values to each PHI we are inserting on the first time we see the edge.
// Check to see if APN already has incoming values from Pred. This also
// prevents us from modifying PHI nodes that are not currently being
// inserted.
bool HasPredEntries = false;
for (unsigned i = 0, e = APN->getNumIncomingValues(); i != e; ++i) {
if (APN->getIncomingBlock(i) == Pred) {
HasPredEntries = true;
break;
}
}
// If we have PHI nodes to update, compute the number of edges from Pred to // If we have PHI nodes to update, compute the number of edges from Pred to
// BB. // BB.
if (!HasPredEntries) { if (PhiToAllocaMap.count(APN)) {
// We want to be able to distinguish between PHI nodes being inserted by // We want to be able to distinguish between PHI nodes being inserted by
// this invocation of mem2reg from those phi nodes that already existed in // this invocation of mem2reg from those phi nodes that already existed in
// the IR before mem2reg was run. We determine that APN is being inserted // the IR before mem2reg was run. We determine that APN is being inserted
@ -983,14 +970,19 @@ NextIteration:
succ_iterator I = succ_begin(BB), E = succ_end(BB); succ_iterator I = succ_begin(BB), E = succ_end(BB);
if (I == E) return; if (I == E) return;
// Handle the last successor without using the worklist. This allows us to // Keep track of the successors so we don't visit the same successor twice
// handle unconditional branches directly, for example. SmallPtrSet<BasicBlock*, 8> VisitedSuccs;
--E;
for (; I != E; ++I)
Worklist.push_back(RenamePassData(*I, BB, IncomingVals));
// Handle the first successor without using the worklist.
VisitedSuccs.insert(*I);
Pred = BB; Pred = BB;
BB = *I; BB = *I;
++I;
for (; I != E; ++I)
if (VisitedSuccs.insert(*I))
Worklist.push_back(RenamePassData(*I, Pred, IncomingVals));
goto NextIteration; goto NextIteration;
} }