[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

diff --git a/llvm/lib/Analysis/ConstantFolding.cpp b/llvm/lib/Analysis/ConstantFolding.cpp
index 3b4e603..74468e8 100644 (file)
--- 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");

diff --git a/llvm/test/Transforms/ConstProp/calls.ll b/llvm/test/Transforms/ConstProp/calls.ll
index 161637c..12ee1cb 100644 (file)
--- a/llvm/test/Transforms/ConstProp/calls.ll
+++ b/llvm/test/Transforms/ConstProp/calls.ll
@@ -193,4 +193,14 @@ entry:
   ret double %0
 }
 
+define float @test_intrinsic_pow_f32_overflow() nounwind uwtable ssp {
+entry:
+; CHECK-LABEL: @test_intrinsic_pow_f32_overflow(
+; CHECK-NOT: call
+; CHECK: ret float 0x7FF0000000000000
+  %0 = call float @llvm.pow.f32(float 40.0, float 50.0)
+  ret float %0
+}
+
 declare double @llvm.pow.f64(double, double) nounwind readonly
+declare float @llvm.pow.f32(float, float) nounwind readonly