[Sema] Refactor IsFunctionConversion

A bunch of uses of IsFunctionConversion don't use the third argument and
just make a dummy QualType to pass. This splits IsFunctionConversion
into 2 functions, one that just takes 2 arguments and does the check,
and one that does the actual conversion using the 3rd argument. Both
functions can be const and replace current uses appropriately.

Author: PiJoules

clang/include/clang/Sema/Sema.h

@@ -10240,8 +10240,13 @@ class Sema final : public SemaBase {
   /// Determine whether the conversion from FromType to ToType is a valid
   /// conversion that strips "noexcept" or "noreturn" off the nested function
   /// type.
-  bool IsFunctionConversion(QualType FromType, QualType ToType,
-                            QualType &ResultTy);
+  bool IsFunctionConversion(QualType FromType, QualType ToType) const;
+
+  /// Same as `IsFunctionConversion`, but if this would return true, it sets
+  /// `ResultTy` to `ToType`.
+  bool TryFunctionConversion(QualType FromType, QualType ToType,
+                             QualType &ResultTy) const;
+
   bool DiagnoseMultipleUserDefinedConversion(Expr *From, QualType ToType);
   void DiagnoseUseOfDeletedFunction(SourceLocation Loc, SourceRange Range,
                                     DeclarationName Name,

clang/lib/Sema/SemaExceptionSpec.cpp

@@ -700,12 +700,11 @@ bool Sema::handlerCanCatch(QualType HandlerType, QualType ExceptionType) {
     //    -- a qualification conversion
     //    -- a function pointer conversion
     bool LifetimeConv;
-    QualType Result;
     // FIXME: Should we treat the exception as catchable if a lifetime
     // conversion is required?
     if (IsQualificationConversion(ExceptionType, HandlerType, false,
                                   LifetimeConv) ||
-        IsFunctionConversion(ExceptionType, HandlerType, Result))
+        IsFunctionConversion(ExceptionType, HandlerType))
       return true;
 
     //    -- a standard pointer conversion [...]

clang/lib/Sema/SemaExpr.cpp

@@ -9124,7 +9124,7 @@ static AssignConvertType checkPointerTypesForAssignment(Sema &S,
           diag::warn_typecheck_convert_incompatible_function_pointer_strict,
           Loc) &&
       RHSType->isFunctionPointerType() && LHSType->isFunctionPointerType() &&
-      !S.IsFunctionConversion(RHSType, LHSType, RHSType))
+      !S.TryFunctionConversion(RHSType, LHSType, RHSType))
     return AssignConvertType::IncompatibleFunctionPointerStrict;
 
   // C99 6.5.16.1p1 (constraint 3): both operands are pointers to qualified or
@@ -9188,8 +9188,7 @@ static AssignConvertType checkPointerTypesForAssignment(Sema &S,
       return AssignConvertType::IncompatibleFunctionPointer;
     return AssignConvertType::IncompatiblePointer;
   }
-  if (!S.getLangOpts().CPlusPlus &&
-      S.IsFunctionConversion(ltrans, rtrans, ltrans))
+  if (!S.getLangOpts().CPlusPlus && S.IsFunctionConversion(ltrans, rtrans))
     return AssignConvertType::IncompatibleFunctionPointer;
   if (IsInvalidCmseNSCallConversion(S, ltrans, rtrans))
     return AssignConvertType::IncompatibleFunctionPointer;

clang/lib/Sema/SemaOverload.cpp

@@ -1881,8 +1881,15 @@ ExprResult Sema::PerformImplicitConversion(Expr *From, QualType ToType,
   return PerformImplicitConversion(From, ToType, ICS, Action);
 }
 
-bool Sema::IsFunctionConversion(QualType FromType, QualType ToType,
-                                QualType &ResultTy) {
+bool Sema::TryFunctionConversion(QualType FromType, QualType ToType,
+                                 QualType &ResultTy) const {
+  bool Changed = IsFunctionConversion(FromType, ToType);
+  if (Changed)
+    ResultTy = ToType;
+  return Changed;
+}
+
+bool Sema::IsFunctionConversion(QualType FromType, QualType ToType) const {
   if (Context.hasSameUnqualifiedType(FromType, ToType))
     return false;
 
@@ -1993,7 +2000,6 @@ bool Sema::IsFunctionConversion(QualType FromType, QualType ToType,
   assert(QualType(FromFn, 0).isCanonical());
   if (QualType(FromFn, 0) != CanTo) return false;
 
-  ResultTy = ToType;
   return true;
 }
 
@@ -2232,11 +2238,10 @@ static bool IsStandardConversion(Sema &S, Expr* From, QualType ToType,
       // we can sometimes resolve &foo<int> regardless of ToType, so check
       // if the type matches (identity) or we are converting to bool
       if (!S.Context.hasSameUnqualifiedType(
-                      S.ExtractUnqualifiedFunctionType(ToType), FromType)) {
-        QualType resultTy;
+              S.ExtractUnqualifiedFunctionType(ToType), FromType)) {
         // if the function type matches except for [[noreturn]], it's ok
         if (!S.IsFunctionConversion(FromType,
-              S.ExtractUnqualifiedFunctionType(ToType), resultTy))
+                                    S.ExtractUnqualifiedFunctionType(ToType)))
           // otherwise, only a boolean conversion is standard
           if (!ToType->isBooleanType())
             return false;
@@ -2476,7 +2481,7 @@ static bool IsStandardConversion(Sema &S, Expr* From, QualType ToType,
   // The third conversion can be a function pointer conversion or a
   // qualification conversion (C++ [conv.fctptr], [conv.qual]).
   bool ObjCLifetimeConversion;
-  if (S.IsFunctionConversion(FromType, ToType, FromType)) {
+  if (S.TryFunctionConversion(FromType, ToType, FromType)) {
     // Function pointer conversions (removing 'noexcept') including removal of
     // 'noreturn' (Clang extension).
     SCS.Third = ICK_Function_Conversion;
@@ -5033,7 +5038,6 @@ Sema::CompareReferenceRelationship(SourceLocation Loc,
   // Check for standard conversions we can apply to pointers: derived-to-base
   // conversions, ObjC pointer conversions, and function pointer conversions.
   // (Qualification conversions are checked last.)
-  QualType ConvertedT2;
   if (UnqualT1 == UnqualT2) {
     // Nothing to do.
   } else if (isCompleteType(Loc, OrigT2) &&
@@ -5044,7 +5048,7 @@ Sema::CompareReferenceRelationship(SourceLocation Loc,
            Context.canBindObjCObjectType(UnqualT1, UnqualT2))
     Conv |= ReferenceConversions::ObjC;
   else if (UnqualT2->isFunctionType() &&
-           IsFunctionConversion(UnqualT2, UnqualT1, ConvertedT2)) {
+           IsFunctionConversion(UnqualT2, UnqualT1)) {
     Conv |= ReferenceConversions::Function;
     // No need to check qualifiers; function types don't have them.
     return Ref_Compatible;
@@ -13426,9 +13430,8 @@ class AddressOfFunctionResolver {
 
 private:
   bool candidateHasExactlyCorrectType(const FunctionDecl *FD) {
-    QualType Discard;
     return Context.hasSameUnqualifiedType(TargetFunctionType, FD->getType()) ||
-           S.IsFunctionConversion(FD->getType(), TargetFunctionType, Discard);
+           S.IsFunctionConversion(FD->getType(), TargetFunctionType);
   }
 
   /// \return true if A is considered a better overload candidate for the

clang/lib/Sema/SemaTemplate.cpp

@@ -7665,9 +7665,8 @@ ExprResult Sema::BuildExpressionFromDeclTemplateArgument(
   QualType DestExprType = ParamType.getNonLValueExprType(Context);
   if (!Context.hasSameType(RefExpr.get()->getType(), DestExprType)) {
     CastKind CK;
-    QualType Ignored;
     if (Context.hasSimilarType(RefExpr.get()->getType(), DestExprType) ||
-        IsFunctionConversion(RefExpr.get()->getType(), DestExprType, Ignored)) {
+        IsFunctionConversion(RefExpr.get()->getType(), DestExprType)) {
       CK = CK_NoOp;
     } else if (ParamType->isVoidPointerType() &&
                RefExpr.get()->getType()->isPointerType()) {

clang/lib/Sema/SemaTemplateDeduction.cpp

@@ -1333,7 +1333,7 @@ bool Sema::isSameOrCompatibleFunctionType(QualType P, QualType A) {
     return Context.hasSameType(P, A);
 
   // Noreturn and noexcept adjustment.
-  if (QualType AdjustedParam; IsFunctionConversion(P, A, AdjustedParam))
+  if (QualType AdjustedParam; TryFunctionConversion(P, A, AdjustedParam))
     P = AdjustedParam;
 
   // FIXME: Compatible calling conventions.
@@ -3732,8 +3732,7 @@ CheckOriginalCallArgDeduction(Sema &S, TemplateDeductionInfo &Info,
     // FIXME: Resolve core issue (no number yet): if the original P is a
     // reference type and the transformed A is function type "noexcept F",
     // the deduced A can be F.
-    QualType Tmp;
-    if (A->isFunctionType() && S.IsFunctionConversion(A, DeducedA, Tmp))
+    if (A->isFunctionType() && S.IsFunctionConversion(A, DeducedA))
       return TemplateDeductionResult::Success;
 
     Qualifiers AQuals = A.getQualifiers();
@@ -3770,11 +3769,10 @@ CheckOriginalCallArgDeduction(Sema &S, TemplateDeductionInfo &Info,
   // Also allow conversions which merely strip __attribute__((noreturn)) from
   // function types (recursively).
   bool ObjCLifetimeConversion = false;
-  QualType ResultTy;
   if ((A->isAnyPointerType() || A->isMemberPointerType()) &&
       (S.IsQualificationConversion(A, DeducedA, false,
                                    ObjCLifetimeConversion) ||
-       S.IsFunctionConversion(A, DeducedA, ResultTy)))
+       S.IsFunctionConversion(A, DeducedA)))
     return TemplateDeductionResult::Success;
 
   //    - If P is a class and P has the form simple-template-id, then the