fix incorrect folding of icmp with undef, PR6481.

llvm-svn: 97659

2 files changed, 4 insertions, 5 deletions

diff --git a/llvm/lib/Analysis/InstructionSimplify.cpp b/llvm/lib/Analysis/InstructionSimplify.cpp
index 1f8053afe94..8288e96eb77 100644
--- a/llvm/lib/Analysis/InstructionSimplify.cpp
+++ b/llvm/lib/Analysis/InstructionSimplify.cpp
@@ -194,11 +194,10 @@ Value *llvm::SimplifyICmpInst(unsigned Predicate, Value *LHS, Value *RHS,
   const Type *ITy = GetCompareTy(LHS);
   
   // icmp X, X -> true/false
-  if (LHS == RHS)
+  // X icmp undef -> true/false.  For example, icmp ugt %X, undef -> false
+  // because X could be 0.
+  if (LHS == RHS || isa<UndefValue>(RHS))
     return ConstantInt::get(ITy, CmpInst::isTrueWhenEqual(Pred));
-
-  if (isa<UndefValue>(RHS))                  // X icmp undef -> undef
-    return UndefValue::get(ITy);
   
   // icmp <global/alloca*/null>, <global/alloca*/null> - Global/Stack value
   // addresses never equal each other!  We already know that Op0 != Op1.
diff --git a/llvm/lib/VMCore/ConstantFold.cpp b/llvm/lib/VMCore/ConstantFold.cpp
index 194a6d4d8c0..47244a0e323 100644
--- a/llvm/lib/VMCore/ConstantFold.cpp
+++ b/llvm/lib/VMCore/ConstantFold.cpp
@@ -1818,7 +1818,7 @@ Constant *llvm::ConstantFoldCompareInstruction(unsigned short pred,
 
   // Handle some degenerate cases first
   if (isa<UndefValue>(C1) || isa<UndefValue>(C2))
-    return UndefValue::get(ResultTy);
+    return ConstantInt::get(ResultTy, CmpInst::isTrueWhenEqual(pred));
 
   // No compile-time operations on this type yet.
   if (C1->getType()->isPPC_FP128Ty())