Make uitofp and sitofp defined on overflow.

IEEE 754 defines the expected result on overflow. As far as I know,
hardware implementations (of f16), and compiler-rt (__floatuntisf)
correctly return +-Inf on overflow. And I can't think of any useful
transform that would take advantage of overflow being undefined here.

Differential Revision: https://reviews.llvm.org/D47807

llvm-svn: 334777

1 files changed, 2 insertions, 7 deletions

diff --git a/llvm/lib/IR/ConstantFold.cpp b/llvm/lib/IR/ConstantFold.cpp
index 218adb4..514a534 100644
--- a/llvm/lib/IR/ConstantFold.cpp
+++ b/llvm/lib/IR/ConstantFold.cpp
@@ -682,13 +682,8 @@ Constant *llvm::ConstantFoldCastInstruction(unsigned opc, Constant *V,
       const APInt &api = CI->getValue();
       APFloat apf(DestTy->getFltSemantics(),
                   APInt::getNullValue(DestTy->getPrimitiveSizeInBits()));
-      if (APFloat::opOverflow &
-          apf.convertFromAPInt(api, opc==Instruction::SIToFP,
-                              APFloat::rmNearestTiesToEven)) {
-        // Undefined behavior invoked - the destination type can't represent
-        // the input constant.
-        return UndefValue::get(DestTy);
-      }
+      apf.convertFromAPInt(api, opc==Instruction::SIToFP,
+                           APFloat::rmNearestTiesToEven);
       return ConstantFP::get(V->getContext(), apf);
     }
     return nullptr;