Incur l-value conversion cost during overload resolution. (#3195)

* Incur l-value conversion cost during overload resolution.

* Fix compile error.

* cleanup.

---------

Co-authored-by: Yong He <yhe@nvidia.com>

5 files changed, 140 insertions, 89 deletions

diff --git a/source/slang/slang-ast-support-types.h b/source/slang/slang-ast-support-types.h
index 5d7ca49cb..0b4e9cab2 100644
--- a/source/slang/slang-ast-support-types.h
+++ b/source/slang/slang-ast-support-types.h
@@ -140,6 +140,9 @@ namespace Slang
         // the element type of the vector)
         kConversionCost_ScalarToVector = 1,
 
+        // Additional cost when casting an LValue.
+        kConversionCost_LValueCast = 800,
+
         // Conversion is impossible
         kConversionCost_Impossible = 0xFFFFFFFF,
     };
@@ -521,6 +524,13 @@ namespace Slang
 
         QualType(Type* type);
 
+        QualType(Type* type, bool isLVal)
+            : QualType(type)
+        {
+            isLeftValue = isLVal;
+        }
+
+
         Type* Ptr() { return type; }
 
         operator Type*() { return type; }
diff --git a/source/slang/slang-check-constraint.cpp b/source/slang/slang-check-constraint.cpp
index 6e600c4af..996b88f48 100644
--- a/source/slang/slang-check-constraint.cpp
+++ b/source/slang/slang-check-constraint.cpp
@@ -174,8 +174,8 @@ namespace Slang
     }
 
     Type* SemanticsVisitor::TryJoinTypes(
-        Type*  left,
-        Type*  right)
+        QualType left,
+        QualType right)
     {
         // Easy case: they are the same type!
         if (left->equals(right))
@@ -186,8 +186,8 @@ namespace Slang
         {
             if (auto rightBasic = as<BasicExpressionType>(right))
             {
-                auto costConvertRightToLeft = getConversionCost(leftBasic, rightBasic);
-                auto costConvertLeftToRight = getConversionCost(rightBasic, leftBasic);
+                auto costConvertRightToLeft = getConversionCost(leftBasic, right);
+                auto costConvertLeftToRight = getConversionCost(rightBasic, left);
 
                 // Return the one that had lower conversion cost.
                 if (costConvertRightToLeft > costConvertLeftToRight)
@@ -217,8 +217,8 @@ namespace Slang
 
                 // Try to join the element types
                 auto joinElementType = TryJoinTypes(
-                    leftVector->getElementType(),
-                    rightVector->getElementType());
+                    QualType(leftVector->getElementType(), left.isLeftValue),
+                    QualType(rightVector->getElementType(), right.isLeftValue));
                 if(!joinElementType)
                     return nullptr;
 
@@ -339,13 +339,13 @@ namespace Slang
                     continue;
                 }
 
-                Type* type = nullptr;
+                QualType type;
                 for (auto& c : system->constraints)
                 {
                     if (c.decl != typeParam.getDecl())
                         continue;
 
-                    auto cType = as<Type>(c.val);
+                    auto cType = QualType(as<Type>(c.val), c.isUsedAsLValue);
                     SLANG_RELEASE_ASSERT(cType);
 
                     if (!type)
@@ -360,7 +360,7 @@ namespace Slang
                             // failure!
                             return DeclRef<Decl>();
                         }
-                        type = joinType;
+                        type = QualType(joinType, type.isLeftValue || cType.isLeftValue);
                     }
 
                     c.satisfied = true;
@@ -505,14 +505,16 @@ namespace Slang
     bool SemanticsVisitor::TryUnifyVals(
         ConstraintSystem&	constraints,
         Val*			fst,
-        Val*			snd)
+        bool            fstLVal,
+        Val*			snd,
+        bool            sndLVal)
     {
         // if both values are types, then unify types
         if (auto fstType = as<Type>(fst))
         {
             if (auto sndType = as<Type>(snd))
             {
-                return TryUnifyTypes(constraints, fstType, sndType);
+                return TryUnifyTypes(constraints, QualType(fstType, fstLVal), QualType(sndType, sndLVal));
             }
         }
 
@@ -582,7 +584,9 @@ namespace Slang
     bool SemanticsVisitor::tryUnifyDeclRef(
         ConstraintSystem& constraints,
         DeclRefBase* fst,
-        DeclRefBase* snd)
+        bool fstIsLVal,
+        DeclRefBase* snd,
+        bool sndIsLVal)
     {
         if (fst == snd)
             return true;
@@ -594,13 +598,15 @@ namespace Slang
             return true;
         if (fstGen == nullptr || sndGen == nullptr)
             return false;
-        return tryUnifyGenericAppDeclRef(constraints, fstGen, sndGen);
+        return tryUnifyGenericAppDeclRef(constraints, fstGen, fstIsLVal, sndGen, sndIsLVal);
     }
 
     bool SemanticsVisitor::tryUnifyGenericAppDeclRef(
         ConstraintSystem&           constraints,
         GenericAppDeclRef* fst,
-        GenericAppDeclRef* snd)
+        bool fstIsLVal,
+        GenericAppDeclRef* snd,
+        bool sndIsLVal)
     {
         SLANG_ASSERT(fst);
         SLANG_ASSERT(snd);
@@ -617,7 +623,7 @@ namespace Slang
         bool okay = true;
         for (Index aa = 0; aa < argCount; ++aa)
         {
-            if (!TryUnifyVals(constraints, fstGen->getArgs()[aa], sndGen->getArgs()[aa]))
+            if (!TryUnifyVals(constraints, fstGen->getArgs()[aa], fstIsLVal, sndGen->getArgs()[aa], sndIsLVal))
             {
                 okay = false;
             }
@@ -627,7 +633,7 @@ namespace Slang
         auto fstBase = fst->getBase();
         auto sndBase = snd->getBase();
 
-        if (!tryUnifyDeclRef(constraints, fstBase, sndBase))
+        if (!tryUnifyDeclRef(constraints, fstBase, fstIsLVal, sndBase, sndIsLVal))
         {
             okay = false;
         }
@@ -636,16 +642,16 @@ namespace Slang
     }
 
     bool SemanticsVisitor::TryUnifyTypeParam(
-        ConstraintSystem&				constraints,
+        ConstraintSystem&		constraints,
         GenericTypeParamDecl*	typeParamDecl,
-        Type*			type)
+        QualType			type)
     {
         // We want to constrain the given type parameter
         // to equal the given type.
         Constraint constraint;
         constraint.decl = typeParamDecl;
         constraint.val = type;
-
+        constraint.isUsedAsLValue = type.isLeftValue;
         constraints.constraints.add(constraint);
 
         return true;
@@ -691,8 +697,8 @@ namespace Slang
 
     bool SemanticsVisitor::TryUnifyTypesByStructuralMatch(
         ConstraintSystem&       constraints,
-        Type*  fst,
-        Type*  snd)
+        QualType  fst,
+        QualType  snd)
     {
         if (auto fstDeclRefType = as<DeclRefType>(fst))
         {
@@ -718,14 +724,17 @@ namespace Slang
                 if (!tryUnifyDeclRef(
                     constraints,
                     fstDeclRef,
-                    sndDeclRef))
+                    fst.isLeftValue,
+                    sndDeclRef,
+                    snd.isLeftValue))
                 {
                     return false;
                 }
 
                 return true;
             }
-        } else if(auto fstFunType = as<FuncType>(fst))
+        }
+        else if(auto fstFunType = as<FuncType>(fst))
         {
             if (auto sndFunType = as<FuncType>(snd))
             {
@@ -746,8 +755,8 @@ namespace Slang
 
     bool SemanticsVisitor::TryUnifyConjunctionType(
         ConstraintSystem&   constraints,
-        Type*               fst,
-        Type*               snd)
+        QualType            fst,
+        QualType            snd)
     {
         // Unifying a type `A & B` with `T` amounts to unifying
         // `A` with `T` and also `B` with `T` while
@@ -759,13 +768,13 @@ namespace Slang
         //
         if (auto fstAndType = as<AndType>(fst))
         {
-            return TryUnifyTypes(constraints, fstAndType->getLeft(), snd)
-                && TryUnifyTypes(constraints, fstAndType->getRight(), snd);
+            return TryUnifyTypes(constraints, QualType(fstAndType->getLeft(), fst.isLeftValue), snd)
+                && TryUnifyTypes(constraints, QualType(fstAndType->getRight(), fst.isLeftValue), snd);
         }
         else if (auto sndAndType = as<AndType>(snd))
         {
-            return TryUnifyTypes(constraints, fst, sndAndType->getLeft())
-                || TryUnifyTypes(constraints, fst, sndAndType->getRight());
+            return TryUnifyTypes(constraints, fst, QualType(sndAndType->getLeft(), snd.isLeftValue))
+                || TryUnifyTypes(constraints, fst, QualType(sndAndType->getRight(), snd.isLeftValue));
         }
         else
             return false;
@@ -773,8 +782,8 @@ namespace Slang
 
     bool SemanticsVisitor::TryUnifyTypes(
         ConstraintSystem&       constraints,
-        Type*  fst,
-        Type*  snd)
+        QualType  fst,
+        QualType  snd)
     {
         if (!fst) return false;
 
@@ -843,8 +852,8 @@ namespace Slang
             {
                 return TryUnifyTypes(
                     constraints,
-                    fstVectorType->getElementType(),
-                    sndScalarType);
+                    QualType(fstVectorType->getElementType(), fst.isLeftValue),
+                    QualType(sndScalarType, snd.isLeftValue));
             }
         }
 
@@ -854,8 +863,8 @@ namespace Slang
             {
                 return TryUnifyTypes(
                     constraints,
-                    fstScalarType,
-                    sndVectorType->getElementType());
+                    QualType(fstScalarType, fst.isLeftValue),
+                    QualType(sndVectorType->getElementType(), snd.isLeftValue));
             }
         }
 
diff --git a/source/slang/slang-check-conversion.cpp b/source/slang/slang-check-conversion.cpp
index 5a9c8df12..c4efba658 100644
--- a/source/slang/slang-check-conversion.cpp
+++ b/source/slang/slang-check-conversion.cpp
@@ -705,7 +705,7 @@ namespace Slang
         CoercionSite site,
         Type*    toType,
         Expr**   outToExpr,
-        Type*    fromType,
+        QualType fromType,
         Expr*    fromExpr,
         ConversionCost* outCost)
     {
@@ -773,7 +773,7 @@ namespace Slang
             auto toBase = toModified ? toModified->getBase() : toType;
             //
             auto fromModified = as<ModifiedType>(fromType);
-            auto fromBase = fromModified ? fromModified->getBase() : fromType;
+            auto fromBase = fromModified ? QualType(fromModified->getBase(), fromType.isLeftValue) : fromType;
 
 
             if((toModified || fromModified) && toBase->equals(fromBase))
@@ -1060,7 +1060,7 @@ namespace Slang
         OverloadResolveContext overloadContext;
         overloadContext.disallowNestedConversions = true;
         overloadContext.argCount = 1;
-        overloadContext.argTypes = &fromType;
+        overloadContext.argTypes = &fromType.type;
         overloadContext.args = &fromExpr;
 
         overloadContext.originalExpr = nullptr;
@@ -1191,6 +1191,11 @@ namespace Slang
                     }
                 }
             }
+            if (fromType.isLeftValue)
+            {
+                // If we are implicitly casting the type of an l-value, we need to impose additional cost.
+                cost += kConversionCost_LValueCast;
+            }
             if(outCost)
                 *outCost = cost;
 
@@ -1245,7 +1250,7 @@ namespace Slang
 
     bool SemanticsVisitor::canCoerce(
         Type*    toType,
-        Type*    fromType,
+        QualType fromType,
         Expr*    fromExpr,
         ConversionCost* outCost)
     {
@@ -1380,7 +1385,7 @@ namespace Slang
 
     bool SemanticsVisitor::canConvertImplicitly(
         Type* toType,
-        Type* fromType)
+        QualType fromType)
     {
         auto conversionCost = getConversionCost(toType, fromType);
 
@@ -1391,7 +1396,7 @@ namespace Slang
         return true;
     }
 
-    ConversionCost SemanticsVisitor::getConversionCost(Type* toType, Type* fromType)
+    ConversionCost SemanticsVisitor::getConversionCost(Type* toType, QualType fromType)
     {
         ConversionCost conversionCost = kConversionCost_Impossible;
         if (!canCoerce(toType, fromType, nullptr, &conversionCost))
diff --git a/source/slang/slang-check-impl.h b/source/slang/slang-check-impl.h
index 37dcba3f4..544bbe170 100644
--- a/source/slang/slang-check-impl.h
+++ b/source/slang/slang-check-impl.h
@@ -46,7 +46,8 @@ namespace Slang
         uint32_t dim2 : 4;
         uint32_t knownConstantBitCount : 8;
         uint32_t knownNegative : 1;
-        uint32_t reserved : 7;
+        uint32_t isLValue : 1;
+        uint32_t reserved : 6;
         uint32_t getRaw() const
         {
             uint32_t val;
@@ -57,16 +58,16 @@ namespace Slang
         {
             return getRaw() == other.getRaw();
         }
-        static BasicTypeKey invalid() { return BasicTypeKey{ 0xff, 0, 0, 0, 0, 0 }; }
+        static BasicTypeKey invalid() { return BasicTypeKey{ 0xff, 0, 0, 0, 0, 0, 0 }; }
     };
 
-    SLANG_FORCE_INLINE BasicTypeKey makeBasicTypeKey(BaseType baseType, IntegerLiteralValue dim1 = 0, IntegerLiteralValue dim2 = 0)
+    SLANG_FORCE_INLINE BasicTypeKey makeBasicTypeKey(BaseType baseType, IntegerLiteralValue dim1 = 0, IntegerLiteralValue dim2 = 0, bool inIsLValue = false)
     {
         SLANG_ASSERT(dim1 >= 0 && dim2 >= 0);
-        return BasicTypeKey{ uint8_t(baseType), uint8_t(dim1), uint8_t(dim2), 0, 0, 0 };
+        return BasicTypeKey{ uint8_t(baseType), uint8_t(dim1), uint8_t(dim2), 0, 0, (inIsLValue?1u:0u), 0 };
     }
 
-    inline BasicTypeKey makeBasicTypeKey(Type* typeIn, Expr* exprIn = nullptr)
+    inline BasicTypeKey makeBasicTypeKey(QualType typeIn, Expr* exprIn = nullptr)
     {
         if (auto basicType = as<BasicExpressionType>(typeIn))
         {
@@ -79,6 +80,7 @@ namespace Slang
                 }
                 rs.knownConstantBitCount = getIntValueBitSize(constInt->value);
             }
+            rs.isLValue = typeIn.isLeftValue ? 1u : 0u;
             return rs;
         }
         else if (auto vectorType = as<VectorExpressionType>(typeIn))
@@ -87,7 +89,7 @@ namespace Slang
             {
                 if( auto elemBasicType = as<BasicExpressionType>(vectorType->getElementType()) )
                 {
-                    return makeBasicTypeKey(elemBasicType->getBaseType(), elemCount->getValue());
+                    return makeBasicTypeKey(elemBasicType->getBaseType(), elemCount->getValue(), 0, typeIn.isLeftValue);
                 }
             }
         }
@@ -99,7 +101,7 @@ namespace Slang
                 {
                     if( auto elemBasicType = as<BasicExpressionType>(matrixType->getElementType()) )
                     {
-                        return makeBasicTypeKey(elemBasicType->getBaseType(), elemCount1->getValue(), elemCount2->getValue());
+                        return makeBasicTypeKey(elemBasicType->getBaseType(), elemCount1->getValue(), elemCount2->getValue(), typeIn.isLeftValue);
                     }
                 }
             }
@@ -144,7 +146,7 @@ namespace Slang
 
             for (Index i = 0; i < opExpr->arguments.getCount(); i++)
             {
-                auto key = makeBasicTypeKey(opExpr->arguments[i]->type.Ptr(), opExpr->arguments[i]);
+                auto key = makeBasicTypeKey(opExpr->arguments[i]->type, opExpr->arguments[i]);
                 if (key.getRaw() == BasicTypeKey::invalid().getRaw())
                 {
                     return false;
@@ -1352,7 +1354,7 @@ namespace Slang
             CoercionSite site,
             Type*    toType,
             Expr**   outToExpr,
-            Type*    fromType,
+            QualType fromType,
             Expr*    fromExpr,
             ConversionCost* outCost);
 
@@ -1365,7 +1367,7 @@ namespace Slang
             ///
         bool canCoerce(
             Type*    toType,
-            Type*    fromType,
+            QualType fromType,
             Expr*    fromExpr,
             ConversionCost* outCost = 0);
 
@@ -1815,6 +1817,7 @@ namespace Slang
         {
             Decl*		decl = nullptr; // the declaration of the thing being constraints
             Val*	val = nullptr; // the value to which we are constraining it
+            bool isUsedAsLValue = false;   // If this constraint is for a type parameter, is the type used in an l-value parameter?
             bool satisfied = false; // Has this constraint been met?
         };
 
@@ -1909,9 +1912,9 @@ namespace Slang
         /// Does there exist an implicit conversion from `fromType` to `toType`?
         bool canConvertImplicitly(
             Type* toType,
-            Type* fromType);
+            QualType fromType);
 
-        ConversionCost getConversionCost(Type* toType, Type* fromType);
+        ConversionCost getConversionCost(Type* toType, QualType fromType);
 
         Type* _tryJoinTypeWithInterface(
             Type*                   type,
@@ -1919,8 +1922,8 @@ namespace Slang
 
         // Try to compute the "join" between two types
         Type* TryJoinTypes(
-            Type*  left,
-            Type*  right);
+            QualType  left,
+            QualType  right);
 
         // Try to solve a system of generic constraints.
         // The `system` argument provides the constraints.
@@ -1965,7 +1968,7 @@ namespace Slang
 
             Index getArgCount() { return argCount; }
             Expr*& getArg(Index index) { return args[index]; }
-            Type*& getArgType(Index index)
+            Type* getArgType(Index index)
             {
                 if(argTypes)
                     return argTypes[index];
@@ -2147,22 +2150,28 @@ namespace Slang
         bool TryUnifyVals(
             ConstraintSystem&	constraints,
             Val*			fst,
-            Val*			snd);
+            bool            fstLVal,
+            Val*			snd,
+            bool            sndLVal);
 
         bool tryUnifyDeclRef(
             ConstraintSystem&       constraints,
             DeclRefBase*   fst,
-            DeclRefBase*   snd);
+            bool           fstLVal,
+            DeclRefBase*   snd,
+            bool           sndLVal);
 
         bool tryUnifyGenericAppDeclRef(
             ConstraintSystem& constraints,
             GenericAppDeclRef* fst,
-            GenericAppDeclRef* snd);
+            bool            fstLVal,
+            GenericAppDeclRef* snd,
+            bool            sndLVal);
 
         bool TryUnifyTypeParam(
-            ConstraintSystem&				constraints,
-            GenericTypeParamDecl*	typeParamDecl,
-            Type*			type);
+            ConstraintSystem&     constraints,
+            GenericTypeParamDecl* typeParamDecl,
+            QualType              type);
 
         bool TryUnifyIntParam(
             ConstraintSystem&               constraints,
@@ -2176,18 +2185,18 @@ namespace Slang
 
         bool TryUnifyTypesByStructuralMatch(
             ConstraintSystem&       constraints,
-            Type*  fst,
-            Type*  snd);
+            QualType fst,
+            QualType snd);
 
         bool TryUnifyTypes(
             ConstraintSystem&       constraints,
-            Type*  fst,
-            Type*  snd);
+            QualType fst,
+            QualType snd);
 
         bool TryUnifyConjunctionType(
             ConstraintSystem&   constraints,
-            Type*            fst,
-            Type*               snd);
+            QualType            fst,
+            QualType            snd);
 
         // Is the candidate extension declaration actually applicable to the given type
         DeclRef<ExtensionDecl> applyExtensionToType(
@@ -2204,7 +2213,7 @@ namespace Slang
             DeclRef<GenericDecl>    genericDeclRef,
             OverloadResolveContext& context,
             ArrayView<Val*>         knownGenericArgs,
-            List<Type*>             *innerParameterTypes = nullptr);
+            List<QualType>             *innerParameterTypes = nullptr);
 
         void AddTypeOverloadCandidates(
             Type*	        type,
diff --git a/source/slang/slang-check-overload.cpp b/source/slang/slang-check-overload.cpp
index 5e626705a..ac93d6505 100644
--- a/source/slang/slang-check-overload.cpp
+++ b/source/slang/slang-check-overload.cpp
@@ -394,21 +394,44 @@ namespace Slang
         return success;
     }
 
+    static QualType getParamQualType(ASTBuilder* astBuilder, DeclRef<ParamDecl> param)
+    {
+        auto paramType = getType(astBuilder, param);
+        bool isLVal = false;
+        switch (getParameterDirection(param.getDecl()))
+        {
+        case kParameterDirection_InOut:
+        case kParameterDirection_Out:
+        case kParameterDirection_Ref:
+            isLVal = true;
+            break;
+        }
+        return QualType(paramType, isLVal);
+    }
+
+    static QualType getParamQualType(Type* paramType)
+    {
+        if (auto paramDirType = as<ParamDirectionType>(paramType))
+        {
+            if (as<OutTypeBase>(paramDirType) || as<RefType>(paramDirType))
+                return QualType(paramDirType->getValueType(), true);
+        }
+        return paramType;
+    }
+
     bool SemanticsVisitor::TryCheckOverloadCandidateTypes(
         OverloadResolveContext&	context,
         OverloadCandidate&		candidate)
     {
         Index argCount = context.getArgCount();
 
-        List<Type*> paramTypes;
-//        List<DeclRef<ParamDecl>> params;
+        List<QualType> paramTypes;
         switch (candidate.flavor)
         {
         case OverloadCandidate::Flavor::Func:
             for (auto param : getParameters(m_astBuilder, candidate.item.declRef.as<CallableDecl>()))
             {
-                auto paramType = getType(m_astBuilder, param);
-                paramTypes.add(paramType);
+                paramTypes.add(getParamQualType(m_astBuilder, param));
             }
             break;
 
@@ -418,13 +441,7 @@ namespace Slang
                 Count paramCount = funcType->getParamCount();
                 for (Index i = 0; i < paramCount; ++i)
                 {
-                    auto paramType = funcType->getParamType(i);
-
-                    if(auto paramDirectionType = as<ParamDirectionType>(paramType))
-                    {
-                        paramType = paramDirectionType->getValueType();
-                    }
-
+                    auto paramType = getParamQualType(funcType->getParamType(i));
                     paramTypes.add(paramType);
                 }
             }
@@ -445,8 +462,8 @@ namespace Slang
         for (Index ii = 0; ii < argCount; ++ii)
         {
             auto& arg = context.getArg(ii);
-            auto argType = context.getArgType(ii);
             auto paramType = paramTypes[ii];
+            auto argType = QualType(context.getArgType(ii), paramType.isLeftValue);
             if (!paramType)
                 return false;
             if (!argType)
@@ -1318,7 +1335,7 @@ namespace Slang
         DeclRef<GenericDecl>    genericDeclRef,
         OverloadResolveContext& context,
         ArrayView<Val*>         knownGenericArgs,
-        List<Type*>             *innerParameterTypes)
+        List<QualType>          *innerParameterTypes)
     {
         // We have been asked to infer zero or more arguments to
         // `genericDeclRef`, in a context where it is being applied
@@ -1360,13 +1377,13 @@ namespace Slang
 
         if (auto funcDeclRef = as<CallableDecl>(genericDeclRef.getDecl()->inner))
         {
-            List<Type*> paramTypes;
+            List<QualType> paramTypes;
             if (!innerParameterTypes)
             {
                 auto params = getParameters(m_astBuilder, funcDeclRef).toArray();
                 for (auto param : params)
                 {
-                    paramTypes.add(getType(m_astBuilder, param));
+                    paramTypes.add(getParamQualType(m_astBuilder, param));
                 }
                 innerParameterTypes = &paramTypes;
             }
@@ -1408,11 +1425,12 @@ namespace Slang
                 //
                 // So the question is then whether a mismatch during the
                 // unification step should be taken as an immediate failure...
-
+                auto argType = context.getArgTypeForInference(aa, this);
+                auto paramType = (*innerParameterTypes)[aa];
                 TryUnifyTypes(
                     constraints,
-                    context.getArgTypeForInference(aa, this),
-                    (*innerParameterTypes)[aa]);
+                    QualType(argType, paramType.isLeftValue),
+                    paramType);
             }
         }
         else
@@ -1679,10 +1697,10 @@ namespace Slang
                 SLANG_ASSERT(diffFuncType);
 
                 // Extract parameter list from processed type.
-                List<Type*> paramTypes;
+                List<QualType> paramTypes;
 
                 for (Index ii = 0; ii < diffFuncType->getParamCount(); ii++)
-                    paramTypes.add(removeParamDirType(diffFuncType->getParamType(ii)));
+                    paramTypes.add(getParamQualType(diffFuncType->getParamType(ii)));
 
                 // Try to infer generic arguments, based on the updated context.
                 OverloadResolveContext subContext = context;