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fix two significant issues with FoldTwoEntryPHINode:

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first, it can kick in on blocks whose conditions have been
folded to a constant, even though one of the edges will be
trivially folded.

second, it doesn't clean up the "if diamond" that it just 
eliminated away.  This is a problem because other simplifycfg
xforms kick in depending on the order of block visitation,
causing pointless work.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@121762 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner
2010-12-14 08:01:53 +00:00
parent 071edc81f2
commit 60d410d7bb
2 changed files with 16 additions and 3 deletions
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12
lib/Transforms/Utils/SimplifyCFG.cpp
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@ -1148,7 +1148,10 @@ static bool FoldTwoEntryPHINode(PHINode *PN, const TargetData *TD) {
BasicBlock *BB = PN->getParent();
BasicBlock *IfTrue, *IfFalse;
Value *IfCond = GetIfCondition(BB, IfTrue, IfFalse);
if (!IfCond) return false;
if (!IfCond ||
// Don't bother if the branch will be constant folded trivially.
isa<ConstantInt>(IfCond))
return false;
// Okay, we found that we can merge this two-entry phi node into a select.
// Doing so would require us to fold *all* two entry phi nodes in this block.
@ -1243,6 +1246,13 @@ static bool FoldTwoEntryPHINode(PHINode *PN, const TargetData *TD) {
NV->takeName(PN);
PN->eraseFromParent();
}
// At this point, IfBlock1 and IfBlock2 are both empty, so our if statement
// has been flattened. Change DomBlock to jump directly to our new block to
// avoid other simplifycfg's kicking in on the diamond.
TerminatorInst *OldTI = DomBlock->getTerminator();
BranchInst::Create(BB, OldTI);
OldTI->eraseFromParent();
return true;
}