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Factor code for testing whether replacing one value with another

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preserves LCSSA form out of ScalarEvolution and into the LoopInfo
class.  Use it to check that SimplifyInstruction simplifications
are not breaking LCSSA form.  Fixes PR8622.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@119727 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Duncan Sands
2010-11-18 19:59:41 +00:00
parent 707120047e
commit d0c6f3dafd
5 changed files with 72 additions and 37 deletions
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lib/Analysis/ScalarEvolution.cpp
+2 -17
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@@ -2768,25 +2768,10 @@ const SCEV *ScalarEvolution::createNodeForPHI(PHINode *PN) {
// PHI's incoming blocks are in a different loop, in which case doing so
// risks breaking LCSSA form. Instcombine would normally zap these, but
// it doesn't have DominatorTree information, so it may miss cases.
if (Value *V = SimplifyInstruction(PN, TD, DT)) {
Instruction *I = dyn_cast<Instruction>(V);
// Only instructions are problematic for preserving LCSSA form.
if (!I)
if (Value *V = SimplifyInstruction(PN, TD, DT))
if (LI->replacementPreservesLCSSAForm(PN, V))
return getSCEV(V);
// If the instruction is not defined in a loop, then it can be used freely.
Loop *ILoop = LI->getLoopFor(I->getParent());
if (!ILoop)
return getSCEV(I);
// If the instruction is defined in the same loop as the phi node, or in a
// loop that contains the phi node loop as an inner loop, then using it as
// a replacement for the phi node will not break LCSSA form.
Loop *PNLoop = LI->getLoopFor(PN->getParent());
if (ILoop->contains(PNLoop))
return getSCEV(I);
}
// If it's not a loop phi, we can't handle it yet.
return getUnknown(PN);
}