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Teach ScalarEvolution how to fold trunc(undef) and anyext(undef) to undef.

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This helps LSR behave more consistently on bugpoint-reduced testcases.

llvm-svn: 108451
This commit is contained in:
Dan Gohman 2010-07-15 20:02:11 +00:00
parent f5525353b4
commit 04768aa9a5
1 changed files with 14 additions and 0 deletions
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14
lib/Analysis/ScalarEvolution.cpp
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@ -845,6 +845,13 @@ const SCEV *ScalarEvolution::getTruncateExpr(const SCEV *Op,
return getAddRecExpr(Operands, AddRec->getLoop());
}
// As a special case, fold trunc(undef) to undef. We don't want to
// know too much about SCEVUnknowns, but this special case is handy
// and harmless.
if (const SCEVUnknown *U = dyn_cast<SCEVUnknown>(Op))
if (isa<UndefValue>(U->getValue()))
return getSCEV(UndefValue::get(Ty));
// The cast wasn't folded; create an explicit cast node. We can reuse
// the existing insert position since if we get here, we won't have
// made any changes which would invalidate it.
@ -1163,6 +1170,13 @@ const SCEV *ScalarEvolution::getAnyExtendExpr(const SCEV *Op,
return getAddRecExpr(Ops, AR->getLoop());
}
// As a special case, fold anyext(undef) to undef. We don't want to
// know too much about SCEVUnknowns, but this special case is handy
// and harmless.
if (const SCEVUnknown *U = dyn_cast<SCEVUnknown>(Op))
if (isa<UndefValue>(U->getValue()))
return getSCEV(UndefValue::get(Ty));
// If the expression is obviously signed, use the sext cast value.
if (isa<SCEVSMaxExpr>(Op))
return SExt;