[ConstantFold] Don't try to strip fp -> int bitcasts to simplify icmps

ConstantFold has logic to take icmp (bitcast x to y), null and strip the
bitcast. This makes sense in general, but not if x has floating-point type. In
this case, we'd need a fcmp, not an icmp, and the code will assert. We normally
don't see this situation because we constant fold fp -> int bitcasts, however,
we'll see it for bitcasts of ppc_fp128 -> i128. This is because that bitcast is
Endian-dependent, and as a result, we don't simplify it in ConstantFold (we
could, but no one has yet added the necessary logic). Regardless, ConstantFold
should not depend on that canonicalization for correctness.

llvm-svn: 268534

1 files changed, 4 insertions, 0 deletions

diff --git a/llvm/lib/IR/ConstantFold.cpp b/llvm/lib/IR/ConstantFold.cpp
index 863b2c4bf41..a338d01a83d 100644
--- a/llvm/lib/IR/ConstantFold.cpp
+++ b/llvm/lib/IR/ConstantFold.cpp
@@ -1529,6 +1529,10 @@ static ICmpInst::Predicate evaluateICmpRelation(Constant *V1, Constant *V2,
     case Instruction::BitCast:
     case Instruction::ZExt:
     case Instruction::SExt:
+      // We can't evaluate floating point casts or truncations.
+      if (CE1Op0->getType()->isFloatingPointTy())
+        break;
+
       // If the cast is not actually changing bits, and the second operand is a
       // null pointer, do the comparison with the pre-casted value.
       if (V2->isNullValue() &&