[ConstantFolding] Fix GetConstantFoldFPValue to avoid cast overflow.

Summary:
In C++, the behavior of casting a double value that is beyond the range
of a single precision floating-point to a float value is undefined. This
change replaces such a cast with APFloat::convert to convert the value,
which is consistent with how we convert a double value to a half value.

Reviewers: sanjoy

Subscribers: lebedev.ri, sanjoy, jlebar, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D59500

llvm-svn: 356781

1 files changed, 2 insertions, 4 deletions

diff --git a/llvm/lib/Analysis/ConstantFolding.cpp b/llvm/lib/Analysis/ConstantFolding.cpp
index 3b4e6031566..74468e8dd72 100644
--- a/llvm/lib/Analysis/ConstantFolding.cpp
+++ b/llvm/lib/Analysis/ConstantFolding.cpp
@@ -1517,14 +1517,12 @@ bool llvm::canConstantFoldCallTo(const CallBase *Call, const Function *F) {
 namespace {
 
 Constant *GetConstantFoldFPValue(double V, Type *Ty) {
-  if (Ty->isHalfTy()) {
+  if (Ty->isHalfTy() || Ty->isFloatTy()) {
     APFloat APF(V);
     bool unused;
-    APF.convert(APFloat::IEEEhalf(), APFloat::rmNearestTiesToEven, &unused);
+    APF.convert(Ty->getFltSemantics(), APFloat::rmNearestTiesToEven, &unused);
     return ConstantFP::get(Ty->getContext(), APF);
   }
-  if (Ty->isFloatTy())
-    return ConstantFP::get(Ty->getContext(), APFloat((float)V));
   if (Ty->isDoubleTy())
     return ConstantFP::get(Ty->getContext(), APFloat(V));
   llvm_unreachable("Can only constant fold half/float/double");