Teach ScalarEvolution how to fold trunc(undef) and anyext(undef) to undef.
This helps LSR behave more consistently on bugpoint-reduced testcases.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@108451 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Analysis/ScalarEvolution.cpp b/lib/Analysis/ScalarEvolution.cpp
index 413b3b4..f0bc936 100644
--- a/lib/Analysis/ScalarEvolution.cpp
+++ b/lib/Analysis/ScalarEvolution.cpp
@@ -845,6 +845,13 @@
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 @@
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;