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Add a comment about why ScalarEvolution doesn't recognize non-loop PHIs

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even when they're obvious.

llvm-svn: 75632
This commit is contained in:
Dan Gohman 2009-07-14 14:06:25 +00:00
parent e5683aabc1
commit e69947ca6e
1 changed files with 4 additions and 0 deletions
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4
lib/Analysis/ScalarEvolution.cpp
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@ -2402,6 +2402,10 @@ const SCEV *ScalarEvolution::createNodeForPHI(PHINode *PN) {
return SymbolicName; return SymbolicName;
} }
// It's tempting to recognize PHIs with a unique incoming value, however
// this leads passes like indvars to break LCSSA form. Fortunately, such
// PHIs are rare, as instcombine zaps them.
// If it's not a loop phi, we can't handle it yet. // If it's not a loop phi, we can't handle it yet.
return getUnknown(PN); return getUnknown(PN);
} }