Diagnose invalid fixed point conversion (#80763)

Author: PiJoules

clang/include/clang/AST/Type.h

@@ -2613,6 +2613,9 @@ class alignas(TypeAlignment) Type : public ExtQualsTypeCommonBase {
   /// Return true if this is a fixed point or integer type.
   bool isFixedPointOrIntegerType() const;
 
+  /// Return true if this can be converted to (or from) a fixed point type.
+  bool isConvertibleToFixedPointType() const;
+
   /// Return true if this is a saturated fixed point type according to
   /// ISO/IEC JTC1 SC22 WG14 N1169. This type can be signed or unsigned.
   bool isSaturatedFixedPointType() const;
@@ -7493,6 +7496,10 @@ inline bool Type::isFixedPointOrIntegerType() const {
   return isFixedPointType() || isIntegerType();
 }
 
+inline bool Type::isConvertibleToFixedPointType() const {
+  return isRealFloatingType() || isFixedPointOrIntegerType();
+}
+
 inline bool Type::isSaturatedFixedPointType() const {
   if (const auto *BT = dyn_cast<BuiltinType>(CanonicalType)) {
     return BT->getKind() >= BuiltinType::SatShortAccum &&

clang/lib/Sema/SemaOverload.cpp

@@ -2177,7 +2177,10 @@ static bool IsStandardConversion(Sema &S, Expr* From, QualType ToType,
              From->isIntegerConstantExpr(S.getASTContext())) {
     SCS.Second = ICK_Compatible_Conversion;
     FromType = ToType;
-  } else if (ToType->isFixedPointType() || FromType->isFixedPointType()) {
+  } else if ((ToType->isFixedPointType() &&
+              FromType->isConvertibleToFixedPointType()) ||
+             (FromType->isFixedPointType() &&
+              ToType->isConvertibleToFixedPointType())) {
     SCS.Second = ICK_Fixed_Point_Conversion;
     FromType = ToType;
   } else {

clang/test/Frontend/fixed_point_errors.cpp

@@ -14,3 +14,7 @@ int fract_int = 10r;     // expected-error{{invalid suffix 'r' on integer consta
 float accum_flt = 0.0k;  // expected-error{{invalid suffix 'k' on floating constant}}
 float fract_flt = 0.0r;  // expected-error{{invalid suffix 'r' on floating constant}}
 #endif
+
+#ifndef WITHOUT_FIXED_POINT
+const char *c = 10.0k;  // expected-error{{cannot initialize a variable of type 'const char *' with an rvalue of type '_Accum'}}
+#endif