add test and handling for atan lib calls

Author: lei137

llvm/lib/Analysis/ConstantFolding.cpp

@@ -2605,6 +2605,9 @@ static Constant *ConstantFoldScalarCall1(StringRef Name,
       break;
     case LibFunc_atan:
     case LibFunc_atanf:
+      // Implement optional behavior from C's Annex F for +/-0.0.
+      if (U.isZero())
+        return ConstantFP::get(Ty->getContext(), U);
       if (TLI->has(Func))
         return ConstantFoldFP(atan, APF, Ty);
       break;

llvm/test/Transforms/InstSimplify/ConstProp/calls.ll

@@ -202,5 +202,17 @@ entry:
   ret float %0
 }
 
+define float @test_atan_negzero() nounwind uwtable ssp {
+entry:
+; CHECK-LABEL: @test_atan_negzero(
+; CHECK:    ret float -0.000000e+00
+;
+; FNOBUILTIN-LABEL: @test_atan_negzero(
+; FNOBUILTIN:  ret float -0.000000e+00
+;
+  %1 = call float @atanf(float -0.0)
+  ret float %1
+}
+
 declare double @llvm.pow.f64(double, double) nounwind readonly
 declare float @llvm.pow.f32(float, float) nounwind readonly