[llvm-commits] [llvm] r108451 - /llvm/trunk/lib/Analysis/ScalarEvolution.cpp

[Dan Gohman]

Author: djg
Date: Thu Jul 15 15:02:11 2010
New Revision: 108451

URL: http://llvm.org/viewvc/llvm-project?rev=108451&view=rev
Log:
Teach ScalarEvolution how to fold trunc(undef) and anyext(undef) to undef.
This helps LSR behave more consistently on bugpoint-reduced testcases.

Modified:
    llvm/trunk/lib/Analysis/ScalarEvolution.cpp

Modified: llvm/trunk/lib/Analysis/ScalarEvolution.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/ScalarEvolution.cpp?rev=108451&r1=108450&r2=108451&view=diff
==============================================================================
--- llvm/trunk/lib/Analysis/ScalarEvolution.cpp (original)
+++ llvm/trunk/lib/Analysis/ScalarEvolution.cpp Thu Jul 15 15:02:11 2010
@@ -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;