[clang] Missed rounding mode use in constant evaluation

Integer-to-float conversion was handled in constant evaluator with
default rounding mode. This change fixes the behavior and the conversion
is made using rounding mode stored in ImplicitCastExpr node.

Differential Revision: https://reviews.llvm.org/D137719

Author: spavloff

clang/lib/AST/ExprConstant.cpp

@@ -2648,14 +2648,9 @@ static bool HandleIntToFloatCast(EvalInfo &Info, const Expr *E,
                                  QualType SrcType, const APSInt &Value,
                                  QualType DestType, APFloat &Result) {
   Result = APFloat(Info.Ctx.getFloatTypeSemantics(DestType), 1);
-  APFloat::opStatus St = Result.convertFromAPInt(Value, Value.isSigned(),
-       APFloat::rmNearestTiesToEven);
-  if (!Info.InConstantContext && St != llvm::APFloatBase::opOK &&
-      FPO.isFPConstrained()) {
-    Info.FFDiag(E, diag::note_constexpr_float_arithmetic_strict);
-    return false;
-  }
-  return true;
+  llvm::RoundingMode RM = getActiveRoundingMode(Info, E);
+  APFloat::opStatus St = Result.convertFromAPInt(Value, Value.isSigned(), RM);
+  return checkFloatingPointResult(Info, E, St);
 }
 
 static bool truncateBitfieldValue(EvalInfo &Info, const Expr *E,

clang/test/AST/const-fpfeatures.c

@@ -1,4 +1,4 @@
-// RUN: %clang_cc1 -fexperimental-strict-floating-point -S -emit-llvm -triple i386-linux -Wno-unknown-pragmas %s -o - | FileCheck %s
+// RUN: %clang_cc1 -S -emit-llvm -triple i386-linux -Wno-unknown-pragmas %s -o - | FileCheck %s
 
 // nextUp(1.F) == 0x1.000002p0F
 
@@ -13,6 +13,9 @@ float F3u = 0x1.000001p0;
 // CHECK: @F2u = {{.*}} float 0x3FF0000020000000
 // CHECK: @F3u = {{.*}} float 0x3FF0000020000000
 
+float FI1u = 0xFFFFFFFFU;
+// CHECK: @FI1u = {{.*}} float 0x41F0000000000000
+
 float _Complex C1u = C0;
 // CHECK: @C1u = {{.*}} { float, float } { float 0x3FF0000020000000, float 0x3FF0000020000000 }
 
@@ -27,5 +30,8 @@ float F3d = 0x1.000001p0;
 // CHECK: @F2d = {{.*}} float 1.000000e+00
 // CHECK: @F3d = {{.*}} float 1.000000e+00
 
+float FI1d = 0xFFFFFFFFU;
+// CHECK: @FI1d = {{.*}} float 0x41EFFFFFE0000000
+
 float _Complex C1d = C0;
 // CHECK: @C1d = {{.*}} { float, float } { float 1.000000e+00, float 1.000000e+00 }