Fix ConstantFold's folding of icmp instructions to recognize that,

for example, a one-past-the-end pointer from one global variable may
be equal to the base pointer of another global variable.

llvm-svn: 173995

1 files changed, 5 insertions, 6 deletions

diff --git a/llvm/lib/IR/ConstantFold.cpp b/llvm/lib/IR/ConstantFold.cpp
index 417e0d1..587b7ce8 100644
--- a/llvm/lib/IR/ConstantFold.cpp
+++ b/llvm/lib/IR/ConstantFold.cpp
@@ -1495,9 +1495,8 @@ static ICmpInst::Predicate evaluateICmpRelation(Constant *V1, Constant *V2,
                    "Surprising getelementptr!");
             return isSigned ? ICmpInst::ICMP_SGT : ICmpInst::ICMP_UGT;
           } else {
-            // If they are different globals, we don't know what the value is,
-            // but they can't be equal.
-            return ICmpInst::ICMP_NE;
+            // If they are different globals, we don't know what the value is.
+            return ICmpInst::BAD_ICMP_PREDICATE;
           }
         }
       } else {
@@ -1510,10 +1509,10 @@ static ICmpInst::Predicate evaluateICmpRelation(Constant *V1, Constant *V2,
         default: break;
         case Instruction::GetElementPtr:
           // By far the most common case to handle is when the base pointers are
-          // obviously to the same or different globals.
+          // obviously to the same global.
           if (isa<GlobalValue>(CE1Op0) && isa<GlobalValue>(CE2Op0)) {
-            if (CE1Op0 != CE2Op0) // Don't know relative ordering, but not equal
-              return ICmpInst::ICMP_NE;
+            if (CE1Op0 != CE2Op0) // Don't know relative ordering.
+              return ICmpInst::BAD_ICMP_PREDICATE;
             // Ok, we know that both getelementptr instructions are based on the
             // same global.  From this, we can precisely determine the relative
             // ordering of the resultant pointers.