Support generic interface methods (#251)

* improve diagnostic messages and prevent fatal errors from crashing the compiler.

* fix top level exception catching.

* spelling fix

* change wording of invalidSwizzleExpr diagnostic

* add speculative GenericsApp expr parsing

* add new test case of cascading generics call.

* Fixing bugs in compiling cascaded generic function calls.

Add implementation of DeclaredSubTypeWitness::SubstituteImpl()

This is not needed by the type checker, but needed by IR specialization. When input source contains cascading generic function call, the arguments to `specialize` instruction is currently represented as a substitution. The arg values of this subsittution can be a `DeclaredSubTypeWitness` when a generic function uses one of its generic parameter to specialize another generic function. When the top level generics function is being specialized, this substitution argument, which is a `DeclaredSubTypeWitness`, needs to be substituted with the witness that used to specialize the top level function in the specialized specialize instruction as well.

* add a test case for cascading generic function call.

* parser bug fix

* fixes #255

* add test case for issue #255

* Generate missing `specialize` instruction when calling a generic method from an interface constraint.

When calling a generic method via an interface, we should be generating the following ir:
...
f = lookup_interface_method(...)
f_s = specailize(f, declRef)
...

This commit fixes this  `emitFuncRef` function to emit the needed `specialize` instruction.

* fixes #260

This fix follows the second apporach in the disucssion. It generated mangled name for specialized functions by appending new substitution type names to the original mangled name.

* Disabling removing and re-inserting specailized functions in getSpecalizeFunc()

I am not sure why it is needed, it seems HLSL and GLSL backends are generating forward declarations anyways, so the order of functions in IRModule shouldn't matter.

* cleanup and complete test cases.

* fix warnings

24 files changed, 524 insertions, 65 deletions

diff --git a/source/core/exception.h b/source/core/exception.h
index aedb62add..fc7aa48e2 100644
--- a/source/core/exception.h
+++ b/source/core/exception.h
@@ -121,6 +121,17 @@ namespace Slang
 		{
 		}
 	};
+
+    class AbortCompilationException : public Exception
+    {
+    public:
+        AbortCompilationException()
+        {}
+        AbortCompilationException(const String & message)
+            : Exception(message)
+        {
+        }
+    };
 }
 
 #endif
\ No newline at end of file
diff --git a/source/slang/check.cpp b/source/slang/check.cpp
index 6bb7c232f..320b22bdb 100644
--- a/source/slang/check.cpp
+++ b/source/slang/check.cpp
@@ -1588,6 +1588,44 @@ namespace Slang
             return true;
         }
 
+        bool doesGenericSignatureMatchRequirement(
+            GenericDecl * genDecl,
+            DeclRef<GenericDecl> requirementGenDecl)
+        {
+            // TODO: genDecl should be a DeclRef to capture the environment generic variables needed to get 
+            // a concrete type for a generic constraint super type (e.g. when this member belongs to a generic type)
+
+            if (genDecl->Members.Count() != requirementGenDecl.getDecl()->Members.Count())
+                return false;
+            for (UInt i = 0; i < genDecl->Members.Count(); i++)
+            {
+                auto genMbr = genDecl->Members[i];
+                auto requiredGenMbr = genDecl->Members[i];
+                if (auto genTypeMbr = genMbr.As<GenericTypeParamDecl>())
+                {
+                    if (auto requiredGenTypeMbr = requiredGenMbr.As<GenericTypeParamDecl>())
+                    {
+                    }
+                    else
+                        return false;
+                }
+                else if (auto genTypeConstraintMbr = genMbr.As<GenericTypeConstraintDecl>())
+                {
+                    if (auto requiredTypeConstraintMbr = requiredGenMbr.As<GenericTypeConstraintDecl>())
+                    {
+                        if (!genTypeConstraintMbr->sup->Equals(requiredTypeConstraintMbr->sup))
+                        {
+                            return false;
+                        }
+                    }
+                    else
+                        return false;
+                }
+            }
+            return doesMemberSatisfyRequirement(genDecl->inner.Ptr(),
+                DeclRef<Decl>(requirementGenDecl.getDecl()->inner.Ptr(), requirementGenDecl.substitutions));
+        }
+
         // Does the given `memberDecl` work as an implementation
         // to satisfy the requirement `requiredMemberDeclRef`
         // from an interface?
@@ -1634,6 +1672,13 @@ namespace Slang
                         requiredInitDecl);
                 }
             }
+            else if (auto genDecl = dynamic_cast<GenericDecl*>(memberDecl))
+            {
+                if (auto requiredGenDeclRef = requiredMemberDeclRef.As<GenericDecl>())
+                {
+                    return doesGenericSignatureMatchRequirement(genDecl, requiredGenDeclRef);
+                }
+            }
             else if (auto subStructTypeDecl = dynamic_cast<AggTypeDecl*>(memberDecl))
             {
                 // this is a sub type (e.g. nested struct declaration) in an aggregate type
@@ -4462,9 +4507,13 @@ namespace Slang
 
             DeclRef<Decl> innerDeclRef(GetInner(baseGenericRef), subst);
 
+            RefPtr<Expr> base;
+            if (auto mbrExpr = baseExpr.As<MemberExpr>())
+                base = mbrExpr->BaseExpression;
+
             return ConstructDeclRefExpr(
                 innerDeclRef,
-                nullptr,
+                base,
                 originalExpr->loc);
         }
 
@@ -5738,7 +5787,6 @@ namespace Slang
             // declarations with the same name, so this becomes a specialized case of
             // overload resolution.
 
-
             // Start by checking the base expression and arguments.
             auto& baseExpr = genericAppExpr->FunctionExpr;
             baseExpr = CheckTerm(baseExpr);
@@ -6095,9 +6143,9 @@ namespace Slang
                 case 'w': case 'a': elementIndex = 3; break;
                 default:
                     // An invalid character in the swizzle is an error
-                    if (!isRewriteMode())
+                    if (!isRewriteMode() && !anyError)
                     {
-                        getSink()->diagnose(swizExpr, Diagnostics::unimplemented, "invalid component name for swizzle");
+                        getSink()->diagnose(swizExpr, Diagnostics::invalidSwizzleExpr, swizzleText, baseElementType->ToString());
                     }
                     anyError = true;
                     continue;
@@ -6109,9 +6157,9 @@ namespace Slang
                 // Make sure the index is in range for the source type
                 if (elementIndex >= limitElement)
                 {
-                    if (!isRewriteMode())
+                    if (!isRewriteMode() && !anyError)
                     {
-                        getSink()->diagnose(swizExpr, Diagnostics::unimplemented, "swizzle component out of range for type");
+                        getSink()->diagnose(swizExpr, Diagnostics::invalidSwizzleExpr, swizzleText, baseElementType->ToString());
                     }
                     anyError = true;
                     continue;
diff --git a/source/slang/diagnostic-defs.h b/source/slang/diagnostic-defs.h
index 10b2dbd1e..7f27e43e8 100644
--- a/source/slang/diagnostic-defs.h
+++ b/source/slang/diagnostic-defs.h
@@ -191,6 +191,7 @@ DIAGNOSTIC(30035, Error, componentOverloadTypeMismatch, "'$0': type of overloade
 DIAGNOSTIC(30041, Error, bitOperationNonIntegral, "bit operation: operand must be integral type.")
 DIAGNOSTIC(30047, Error, argumentExpectedLValue, "argument passed to parameter '$0' must be l-value.")
 DIAGNOSTIC(30051, Error, invalidValueForArgument, "invalid value for argument '$0'")
+DIAGNOSTIC(30052, Error, invalidSwizzleExpr, "invalid swizzle pattern '$0' on type '$1'")
 DIAGNOSTIC(33070, Error, expectedFunction, "expression preceding parenthesis of apparent call must have function type.")
 
 // 303xx: interfaces and associated types
diff --git a/source/slang/diagnostics.cpp b/source/slang/diagnostics.cpp
index f08554b52..18e5f9a4d 100644
--- a/source/slang/diagnostics.cpp
+++ b/source/slang/diagnostics.cpp
@@ -209,7 +209,7 @@ void DiagnosticSink::diagnoseImpl(SourceLoc const& pos, DiagnosticInfo const& in
     if (diagnostic.severity >= Severity::Fatal)
     {
         // TODO: figure out a better policy for aborting compilation
-        throw InvalidOperationException();
+        throw AbortCompilationException();
     }
 }
 
diff --git a/source/slang/emit.cpp b/source/slang/emit.cpp
index 9fda630bf..332125fc6 100644
--- a/source/slang/emit.cpp
+++ b/source/slang/emit.cpp
@@ -4754,7 +4754,7 @@ emitDeclImpl(decl, nullptr);
         void readSimpleIntVal()
         {
             int c = peek();
-            if(isDigit(c))
+            if(isDigit((char)c))
             {
                 get();
             }
diff --git a/source/slang/ir-legalize-types.cpp b/source/slang/ir-legalize-types.cpp
index 677ccedd3..5b42407c2 100644
--- a/source/slang/ir-legalize-types.cpp
+++ b/source/slang/ir-legalize-types.cpp
@@ -469,12 +469,12 @@ static LegalVal legalizeFieldAddress(
                 }
             }
             SLANG_UNEXPECTED("didn't find tuple element");
-            return LegalVal();
+            UNREACHABLE_RETURN(LegalVal());
         }
 
     default:
         SLANG_UNEXPECTED("unhandled");
-        return LegalVal();
+        UNREACHABLE_RETURN(LegalVal());
     }
 }
 
diff --git a/source/slang/ir.cpp b/source/slang/ir.cpp
index 439bc7797..b1af6521c 100644
--- a/source/slang/ir.cpp
+++ b/source/slang/ir.cpp
@@ -55,15 +55,15 @@ namespace Slang
         }
     }
 
-    void IRUse::set(IRValue* usedValue)
+    void IRUse::set(IRValue* usedVal)
     {
         // clear out the old value
-        if (usedValue)
+        if (usedVal)
         {
             *prevLink = nextUse;
         }
 
-        init(user, usedValue);
+        init(user, usedVal);
     }
 
     void IRUse::clear()
@@ -3750,8 +3750,6 @@ namespace Slang
     {
         if( auto subtypeWitness = dynamic_cast<SubtypeWitness*>(val) )
         {
-            // We need to look up the IR value that represents the
-            // given subtype witness.
             String mangledName = getMangledNameForConformanceWitness(
                 subtypeWitness->sub,
                 subtypeWitness->sup);
@@ -3948,8 +3946,11 @@ namespace Slang
         // has already been made. To do that we will need to
         // compute the mangled name of the specialized function,
         // so that we can look for existing declarations.
-
-        String specMangledName = getMangledName(specDeclRef);
+        String specMangledName;
+        if (genericFunc->genericDecl == specDeclRef.decl)
+            specMangledName = getMangledName(specDeclRef);
+        else
+            specMangledName = mangleSpecializedFuncName(genericFunc->mangledName, specDeclRef.substitutions);
 
         // TODO: This is a terrible linear search, and we should
         // avoid it by building a dictionary ahead of time,
@@ -3992,8 +3993,8 @@ namespace Slang
         //
         // TODO: This shouldn't be needed, if we introduce a sorting
         // step before we emit code.
-        specFunc->removeFromParent();
-        specFunc->insertAfter(genericFunc);
+        //specFunc->removeFromParent();
+        //specFunc->insertAfter(genericFunc);
 
         // At this point we've created a new non-generic function,
         // which means we should add it to our work list for
@@ -4026,8 +4027,20 @@ namespace Slang
             auto keyDeclRef = ((IRDeclRef*) requirementKey)->declRef;
 
             // If the keys don't match, continue with the next entry.
-            if(!keyDeclRef.Equals(requirementDeclRef))
-                continue;
+            if (!keyDeclRef.Equals(requirementDeclRef))
+            {
+                // requirementDeclRef may be pointing to the inner decl of a generic decl
+                // in this case we compare keyDeclRef against the parent decl of requiredDeclRef
+                if (auto genRequiredDeclRef = requirementDeclRef.GetParent().As<GenericDecl>())
+                {
+                    if (!keyDeclRef.Equals(genRequiredDeclRef))
+                    {
+                        continue;
+                    }
+                }
+                else
+                    continue;
+            }
 
             // If the keys matched, then we use the value from
             // this entry.
@@ -4178,7 +4191,6 @@ namespace Slang
                             // Use the witness table to look up the value that
                             // satisfies the requirement.
                             auto satisfyingVal = findWitnessVal(witnessTable, requirementDeclRef);
-
                             // We expect to always find something, but lets just
                             // be careful here.
                             if(!satisfyingVal)
diff --git a/source/slang/lower-to-ir.cpp b/source/slang/lower-to-ir.cpp
index 2c64c539b..4fabd6a81 100644
--- a/source/slang/lower-to-ir.cpp
+++ b/source/slang/lower-to-ir.cpp
@@ -314,6 +314,13 @@ LoweredValInfo emitDeclRef(
     IRGenContext*   context,
     DeclRef<Decl>   declRef);
 
+// Emit necessary `specialize` instruction needed by a declRef.
+// This is currently used by emitDeclRef() and emitFuncRef()
+LoweredValInfo maybeEmitSpecializeInst(IRGenContext*   context, 
+    LoweredValInfo loweredDecl,  // the lowered value of the inner decl
+    DeclRef<Decl>   declRef      // the full decl ref containing substitutions
+);
+
 
 IRValue* getSimpleVal(IRGenContext* context, LoweredValInfo lowered);
 
@@ -488,10 +495,11 @@ LoweredValInfo emitFuncRef(
 
                 RefPtr<Type> type = funcExpr->type;
 
-                return LoweredValInfo::simple(context->irBuilder->emitLookupInterfaceMethodInst(
+                auto loweredVal = LoweredValInfo::simple(context->irBuilder->emitLookupInterfaceMethodInst(
                     type,
                     baseMemberDeclRef,
                     funcDeclRef));
+                return maybeEmitSpecializeInst(context, loweredVal, funcDeclRef);
             }
         }
     }
@@ -2893,6 +2901,13 @@ struct DeclLoweringVisitor : DeclVisitor<DeclLoweringVisitor, LoweredValInfo>
         return LoweredValInfo::simple(irFunc);
     }
 
+    LoweredValInfo visitGenericDecl(GenericDecl * genDecl)
+    {
+        if (auto innerFuncDecl = genDecl->inner->As<FuncDecl>())
+            return lowerFuncDecl(innerFuncDecl);
+        SLANG_RELEASE_ASSERT(false);
+        UNREACHABLE_RETURN(LoweredValInfo());
+    }
 
     LoweredValInfo visitFunctionDeclBase(FunctionDeclBase* decl)
     {
@@ -2997,6 +3012,11 @@ RefPtr<Val> lowerSubstitutionArg(
     }
     else if (auto declaredSubtypeWitness = dynamic_cast<DeclaredSubtypeWitness*>(val))
     {
+        // We do not have a concrete witness table yet for a GenericTypeConstraintDecl witness
+
+        if (declaredSubtypeWitness->declRef.As<GenericTypeConstraintDecl>())
+            return val;
+
         // We need to look up the IR-level representation of the witness
         // (which is a witness table).
 
@@ -3073,9 +3093,16 @@ LoweredValInfo emitDeclRef(
     // unspecialized declaration.
     LoweredValInfo loweredDecl = ensureDecl(context, declRef.getDecl());
 
+    return maybeEmitSpecializeInst(context, loweredDecl, declRef);
+}
+
+LoweredValInfo maybeEmitSpecializeInst(IRGenContext*   context,
+    LoweredValInfo loweredDecl,
+    DeclRef<Decl>   declRef)
+{
     // If this declaration reference doesn't involve any specializations,
     // then we are done at this point.
-    if(!hasGenericSubstitutions(declRef.substitutions))
+    if (!hasGenericSubstitutions(declRef.substitutions))
         return loweredDecl;
 
     auto val = getSimpleVal(context, loweredDecl);
@@ -3089,7 +3116,7 @@ LoweredValInfo emitDeclRef(
 
 
     RefPtr<Type> type;
-    if(auto declType = val->getType())
+    if (auto declType = val->getType())
     {
         type = declType->Substitute(declRef.substitutions).As<Type>();
     }
@@ -3102,6 +3129,7 @@ LoweredValInfo emitDeclRef(
         declRef));
 }
 
+
 static void lowerEntryPointToIR(
     IRGenContext*       context,
     EntryPointRequest*  entryPointRequest)
diff --git a/source/slang/mangle.cpp b/source/slang/mangle.cpp
index dca48f671..38c2b29a8 100644
--- a/source/slang/mangle.cpp
+++ b/source/slang/mangle.cpp
@@ -350,6 +350,24 @@ namespace Slang
             DeclRef<Decl>(declRef.decl, declRef.substitutions));
     }
 
+    String mangleSpecializedFuncName(String baseName, RefPtr<Substitutions> subst)
+    {
+        ManglingContext context;
+        emitRaw(&context, baseName.Buffer());
+        emitRaw(&context, "_G");
+        while (subst)
+        {
+            if (auto genSubst = subst.As<GenericSubstitution>())
+            {
+                for (auto a : genSubst->args)
+                    emitVal(&context, a);
+                break;
+            }
+            subst = subst->outer;
+        }
+        return context.sb.ProduceString();
+    }
+
     String getMangledName(Decl* decl)
     {
         return getMangledName(makeDeclRef(decl));
diff --git a/source/slang/mangle.h b/source/slang/mangle.h
index 60a1dff9e..29101a926 100644
--- a/source/slang/mangle.h
+++ b/source/slang/mangle.h
@@ -11,7 +11,7 @@ namespace Slang
     String getMangledName(Decl* decl);
     String getMangledName(DeclRef<Decl> const & declRef);
     String getMangledName(DeclRefBase const & declRef);
-
+    String mangleSpecializedFuncName(String baseName, RefPtr<Substitutions> subst);
     String getMangledNameForConformanceWitness(
         Type* sub,
         Type* sup);
diff --git a/source/slang/parser.cpp b/source/slang/parser.cpp
index 595d58d7e..eb02d98c5 100644
--- a/source/slang/parser.cpp
+++ b/source/slang/parser.cpp
@@ -77,7 +77,7 @@ namespace Slang
             , sink(sink)
             , outerScope(outerScope)
         {}
-
+        Parser(const Parser & other) = default;
         Session* getSession()
         {
             return translationUnit->compileRequest->mSession;
@@ -1396,6 +1396,69 @@ namespace Slang
         return genericApp;
     }
 
+    static bool isGenericName(Parser* parser, Name* name)
+    {
+        auto lookupResult = lookUp(
+            parser->getSession(),
+            nullptr, // no semantics visitor available yet
+            name,
+            parser->currentScope);
+        if (!lookupResult.isValid() || lookupResult.isOverloaded())
+            return false;
+
+        auto decl = lookupResult.item.declRef.getDecl();
+        if (auto genericDecl = dynamic_cast<GenericDecl*>(decl))
+        {
+            return true;
+        }
+        else
+        {
+            return false;
+        }
+    }
+
+    static RefPtr<Expr> tryParseGenericApp(
+        Parser*                         parser,
+        RefPtr<Expr>    base)
+    {
+        Name * baseName = nullptr;
+        if (auto varExpr = base->As<VarExpr>())
+            baseName = varExpr->name;
+        // if base is a known generics, parse as generics
+        if (baseName && isGenericName(parser, baseName))
+            return parseGenericApp(parser, base);
+
+        // otherwise, we speculate as generics, and fallback to comparison when parsing failed
+        TokenSpan tokenSpan;
+        tokenSpan.mBegin = parser->tokenReader.mCursor;
+        tokenSpan.mEnd = parser->tokenReader.mEnd;
+        DiagnosticSink newSink;
+        newSink.sourceManager = parser->sink->sourceManager;
+        Parser newParser(*parser);
+        newParser.sink = &newSink;
+        auto speculateParseRs = parseGenericApp(&newParser, base);
+        if (newSink.errorCount == 0)
+        {
+            // disambiguate based on FOLLOW set
+            switch (peekTokenType(&newParser))
+            {
+            case TokenType::Dot:
+            case TokenType::LParent:
+            case TokenType::RParent:
+            case TokenType::RBracket:
+            case TokenType::Colon:
+            case TokenType::Comma:
+            case TokenType::QuestionMark:
+            case TokenType::Semicolon:
+            case TokenType::OpEql:
+            case TokenType::OpNeq:
+            {
+                return parseGenericApp(parser, base);
+            }
+            }
+        }
+        return base;
+    }
     static RefPtr<Expr> parseMemberType(Parser * parser, RefPtr<Expr> base)
     {
         RefPtr<MemberExpr> memberExpr = new MemberExpr();
@@ -2624,28 +2687,6 @@ namespace Slang
         return stmt;
     }
 
-    static bool isGenericName(Parser* parser, Name* name)
-    {
-        auto lookupResult = lookUp(
-            parser->getSession(),
-            nullptr, // no semantics visitor available yet
-            name,
-            parser->currentScope);
-        if(!lookupResult.isValid() || lookupResult.isOverloaded())
-            return false;
-
-        auto decl = lookupResult.item.declRef.getDecl();
-        if( auto genericDecl = dynamic_cast<GenericDecl*>(decl) )
-        {
-            return true;
-        }
-        else
-        {
-            return false;
-        }
-    }
-
-
     static bool isTypeName(Parser* parser, Name* name)
     {
         auto lookupResult = lookUp(
@@ -3367,24 +3408,18 @@ namespace Slang
         }
 #endif
     }
-
+    
     // We *might* be looking at an application of a generic to arguments,
     // but we need to disambiguate to make sure.
     static RefPtr<Expr> maybeParseGenericApp(
         Parser*                             parser,
 
         // TODO: need to support more general expressions here
-        RefPtr<VarExpr>     base)
+        RefPtr<Expr>     base)
     {
         if(peekTokenType(parser) != TokenType::OpLess)
             return base;
-
-        if(!isGenericName(parser, base->name))
-            return base;
-
-        // Okay, seems likely that we are looking at a generic app
-
-        return parseGenericApp(parser, base);
+        return tryParseGenericApp(parser, base);
     }
 
     static RefPtr<Expr> parsePrefixExpr(Parser* parser);
@@ -3769,7 +3804,10 @@ namespace Slang
                     parser->ReadToken(TokenType::Dot); 
                     memberExpr->name = expectIdentifier(parser).name;
 
-                    expr = memberExpr;
+                    if (peekTokenType(parser) == TokenType::OpLess)
+                        expr = maybeParseGenericApp(parser, memberExpr);
+                    else
+                        expr = memberExpr;
                 }
                 break;
             }
diff --git a/source/slang/slang.cpp b/source/slang/slang.cpp
index 1cda8e7d0..fe24fbd19 100644
--- a/source/slang/slang.cpp
+++ b/source/slang/slang.cpp
@@ -246,13 +246,13 @@ int CompileRequest::executeActionsInner()
     // Do some cleanup on settings specified by user.
     // In particular, we want to propagate flags from the overall request down to
     // each translation unit.
-    for( auto& translationUnit : translationUnits )
+    for (auto& translationUnit : translationUnits)
     {
         translationUnit->compileFlags |= compileFlags;
 
         // However, the "no checking" flag shouldn't be applied to
         // any translation unit that is native Slang code.
-        if( translationUnit->sourceLanguage == SourceLanguage::Slang )
+        if (translationUnit->sourceLanguage == SourceLanguage::Slang)
         {
             translationUnit->compileFlags &= ~SLANG_COMPILE_FLAG_NO_CHECKING;
         }
@@ -282,7 +282,7 @@ int CompileRequest::executeActionsInner()
     // a pass-through compilation.
     //
     // Note that we *do* perform output generation as normal in pass-through mode.
-    if( passThrough == PassThroughMode::None )
+    if (passThrough == PassThroughMode::None)
     {
         // Parse everything from the input files requested
         for (auto& translationUnit : translationUnits)
@@ -316,7 +316,7 @@ int CompileRequest::executeActionsInner()
                 return 1;
         }
     }
-    
+
     // If command line specifies to skip codegen, we exit here.
     // Note: this is a debugging option.
     if (shouldSkipCodegen)
@@ -901,7 +901,7 @@ SLANG_API int spCompile(
 {
     auto req = REQ(request);
 
-#if 0
+#if !defined(SLANG_DEBUG_INTERNAL_ERROR)
     // By default we'd like to catch as many internal errors as possible,
     // and report them to the user nicely (rather than just crash their
     // application). Internally Slang currently uses exceptions for this.
diff --git a/source/slang/slang.natvis b/source/slang/slang.natvis
index 5bf8a1b09..91e9d0994 100644
--- a/source/slang/slang.natvis
+++ b/source/slang/slang.natvis
@@ -97,4 +97,17 @@
       <ExpandedItem>usedValue</ExpandedItem>
     </Expand>
   </Type>
+  <Type Name="Slang::IRModule">
+    <Expand>
+      <Item Name="session">session</Item>
+      <LinkedListItems>
+        <HeadPointer>firstGlobalValue</HeadPointer>
+        <NextPointer>nextGlobalValue</NextPointer>
+        <ValueNode>this</ValueNode>
+      </LinkedListItems>
+    </Expand>
+  </Type>
+  <Type Name="Slang::IRGlobalValue">
+    <DisplayString>{{IRGlobalValue {op} {mangledName}}}</DisplayString>
+  </Type>
 </AutoVisualizer>
\ No newline at end of file
diff --git a/source/slang/syntax.cpp b/source/slang/syntax.cpp
index 9025c545a..4e1778e6e 100644
--- a/source/slang/syntax.cpp
+++ b/source/slang/syntax.cpp
@@ -1527,6 +1527,61 @@ void Type::accept(IValVisitor* visitor, void* extra)
             && declRef.Equals(otherWitness->declRef);
     }
 
+    RefPtr<Val> DeclaredSubtypeWitness::SubstituteImpl(Substitutions* subst, int * ioDiff)
+    {
+        DeclRef<GenericTypeParamDecl> genParamDeclRef;
+        if (auto subDeclRefType = this->sub.As<DeclRefType>())
+        {
+            genParamDeclRef = subDeclRefType->declRef.As<GenericTypeParamDecl>();
+        }
+        if (!genParamDeclRef)
+            return this;
+        auto genParamDecl = genParamDeclRef.getDecl();
+        // search for a substitution that might apply to us
+        for (auto s = subst; s; s = s->outer.Ptr())
+        {
+            if (auto genericSubst = dynamic_cast<GenericSubstitution*>(s))
+            {
+                // the generic decl associated with the substitution list must be
+                // the generic decl that declared this parameter
+                auto genericDecl = genericSubst->genericDecl;
+                if (genericDecl != genParamDecl->ParentDecl)
+                    continue;
+                bool found = false;
+                int index = 0;
+                for (auto m : genericDecl->Members)
+                {
+                    if (m.Ptr() == genParamDecl)
+                    {
+                        // We've found it, so return the corresponding specialization argument
+                        (*ioDiff)++;
+                        found = true;
+                        break;
+                    }
+                    else if (auto typeParam = m.As<GenericTypeParamDecl>())
+                    {
+                        index++;
+                    }
+                    else if (auto valParam = m.As<GenericValueParamDecl>())
+                    {
+                        index++;
+                    }
+                    else
+                    {
+                    }
+                }
+                if (found)
+                {
+                    auto ordinaryParamCount = genericDecl->getMembersOfType<GenericTypeParamDecl>().Count() +
+                        genericDecl->getMembersOfType<GenericValueParamDecl>().Count();
+                    SLANG_ASSERT(ordinaryParamCount + index < genericSubst->args.Count());
+                    return genericSubst->args[ordinaryParamCount + index];
+                }
+            }
+        }
+        return this;
+    }
+
     String DeclaredSubtypeWitness::ToString()
     {
         StringBuilder sb;
@@ -1655,4 +1710,16 @@ void Type::accept(IValVisitor* visitor, void* extra)
         return false;
     }
 
+    RefPtr<GenericSubstitution> getGenericSubstitution(RefPtr<Substitutions> subst)
+    {
+        auto p = subst.Ptr();
+        while (p)
+        {
+            if (auto genSubst = dynamic_cast<GenericSubstitution*>(p))
+                return genSubst;
+            p = p->outer.Ptr();
+        }
+        return nullptr;
+    }
+
 }
diff --git a/source/slang/syntax.h b/source/slang/syntax.h
index bda43b336..46beca2d9 100644
--- a/source/slang/syntax.h
+++ b/source/slang/syntax.h
@@ -1160,7 +1160,7 @@ namespace Slang
     RefPtr<ThisTypeSubstitution> getThisTypeSubst(DeclRefBase & declRef, bool insertSubstEntry);
     void removeSubstitution(DeclRefBase & declRef, RefPtr<Substitutions> subst);
     bool hasGenericSubstitutions(RefPtr<Substitutions> subst);
-
+    RefPtr<GenericSubstitution> getGenericSubstitution(RefPtr<Substitutions> subst);
 } // namespace Slang
 
 #endif
\ No newline at end of file
diff --git a/source/slang/val-defs.h b/source/slang/val-defs.h
index 4513873e3..5a370d34a 100644
--- a/source/slang/val-defs.h
+++ b/source/slang/val-defs.h
@@ -95,6 +95,7 @@ RAW(
     virtual bool EqualsVal(Val* val) override;
     virtual String ToString() override;
     virtual int GetHashCode() override;
+    virtual RefPtr<Val> SubstituteImpl(Substitutions * subst, int * ioDiff) override;
 )
 END_SYNTAX_CLASS()
 
diff --git a/tests/bugs/nested-generics-call.slang b/tests/bugs/nested-generics-call.slang
new file mode 100644
index 000000000..2c6df59c6
--- /dev/null
+++ b/tests/bugs/nested-generics-call.slang
@@ -0,0 +1,34 @@
+//TEST(compute):COMPARE_COMPUTE:-xslang -use-ir
+//TEST_INPUT:ubuffer(data=[0 0 0 0], stride=4):dxbinding(0),glbinding(0),out
+
+RWStructuredBuffer<float> outputBuffer;
+
+interface IBase
+{
+    float get();
+}
+
+struct BaseImpl : IBase
+{
+    float get() { return 1.0; }
+};
+
+__generic<T:IBase>
+float eval(T obj)
+{
+    return obj.get();
+}
+
+__generic<T : IBase>
+float test(T obj)
+{
+    return eval<T>(obj);
+}
+
+[numthreads(4, 1, 1)]
+void computeMain(uint3 dispatchThreadID : SV_DispatchThreadID)
+{
+    BaseImpl base;
+	float outVal = test<BaseImpl>(base);
+	outputBuffer[dispatchThreadID.x] = outVal;
+}
\ No newline at end of file
diff --git a/tests/bugs/nested-generics-call.slang.expected.txt b/tests/bugs/nested-generics-call.slang.expected.txt
new file mode 100644
index 000000000..cc5e55ab6
--- /dev/null
+++ b/tests/bugs/nested-generics-call.slang.expected.txt
@@ -0,0 +1,4 @@
+3F800000
+3F800000
+3F800000
+3F800000
diff --git a/tests/bugs/nested-generics-method-call.slang b/tests/bugs/nested-generics-method-call.slang
new file mode 100644
index 000000000..d1e80da57
--- /dev/null
+++ b/tests/bugs/nested-generics-method-call.slang
@@ -0,0 +1,38 @@
+//TEST(compute):COMPARE_COMPUTE:-xslang -use-ir
+//TEST_INPUT:ubuffer(data=[0 0 0 0], stride=4):dxbinding(0),glbinding(0),out
+
+RWStructuredBuffer<float> outputBuffer;
+
+interface IBase
+{
+    float get();
+}
+
+struct BaseImpl : IBase
+{
+    float get() { return 1.0; }
+};
+
+struct S
+{
+    __generic<T:IBase>
+    float eval(T obj)
+    {
+        return obj.get();
+    }
+};
+
+__generic<T : IBase>
+float test(T obj)
+{
+    S s;
+    return s.eval<T>(obj);
+}
+
+[numthreads(4, 1, 1)]
+void computeMain(uint3 dispatchThreadID : SV_DispatchThreadID)
+{
+    BaseImpl base;
+	float outVal = test<BaseImpl>(base);
+	outputBuffer[dispatchThreadID.x] = outVal;
+}
\ No newline at end of file
diff --git a/tests/bugs/nested-generics-method-call.slang.expected.txt b/tests/bugs/nested-generics-method-call.slang.expected.txt
new file mode 100644
index 000000000..cc5e55ab6
--- /dev/null
+++ b/tests/bugs/nested-generics-method-call.slang.expected.txt
@@ -0,0 +1,4 @@
+3F800000
+3F800000
+3F800000
+3F800000
diff --git a/tests/compute/generic-interface-method-simple.slang b/tests/compute/generic-interface-method-simple.slang
new file mode 100644
index 000000000..7ba129492
--- /dev/null
+++ b/tests/compute/generic-interface-method-simple.slang
@@ -0,0 +1,48 @@
+//TEST(compute):COMPARE_COMPUTE:-xslang -use-ir
+//TEST_INPUT:ubuffer(data=[0 0 0 0], stride=4):dxbinding(0),glbinding(0),out
+
+RWStructuredBuffer<float> outputBuffer;
+
+interface IVertexInterpolant
+{
+    float2 getUV();
+}
+
+interface IBRDFPattern
+{
+    __generic<TVertexInterpolant:IVertexInterpolant>
+    float evalPattern(TVertexInterpolant interpolants);
+}
+
+struct StandardVertexInterpolant : IVertexInterpolant
+{
+    float2 getUV() { return float2(0.5); }
+};
+
+struct MaterialPattern1 : IBRDFPattern
+{
+    float base;
+    __generic<TVertexInterpolant:IVertexInterpolant>
+    float evalPattern(TVertexInterpolant interpolants)
+    {
+        float rs = base + interpolants.getUV().x;
+        return rs;
+    }
+};
+
+__generic<TPattern : IBRDFPattern, TInterpolant: IVertexInterpolant>
+float test(TPattern pattern, TInterpolant vertInterps)
+{
+    float rs = pattern.evalPattern<TInterpolant>(vertInterps);    
+    return rs;
+}
+
+[numthreads(4, 1, 1)]
+void computeMain(uint3 dispatchThreadID : SV_DispatchThreadID)
+{
+    StandardVertexInterpolant vertInterp;
+    MaterialPattern1 mp1;
+    mp1.base = 0.5;
+	float outVal = test<MaterialPattern1, StandardVertexInterpolant>(mp1, vertInterp);
+	outputBuffer[dispatchThreadID.x] = outVal;
+}
\ No newline at end of file
diff --git a/tests/compute/generic-interface-method-simple.slang.expected.txt b/tests/compute/generic-interface-method-simple.slang.expected.txt
new file mode 100644
index 000000000..e143b7f20
--- /dev/null
+++ b/tests/compute/generic-interface-method-simple.slang.expected.txt
@@ -0,0 +1,4 @@
+3F800000
+3F800000
+3F800000
+3F800000
\ No newline at end of file
diff --git a/tests/compute/generic-interface-method.slang b/tests/compute/generic-interface-method.slang
new file mode 100644
index 000000000..e4fa8cff5
--- /dev/null
+++ b/tests/compute/generic-interface-method.slang
@@ -0,0 +1,86 @@
+//TEST(compute):COMPARE_COMPUTE:-xslang -use-ir
+//TEST_INPUT:ubuffer(data=[0 0 0 0], stride=4):dxbinding(0),glbinding(0),out
+
+RWStructuredBuffer<float> outputBuffer;
+
+struct DisneyBRDFPattern
+{
+    float3 baseColor;
+    float3 normal;
+    float specular, metallic, roughness;
+    float opacity;
+    float3 emmissive;
+    float ambientOcclusion;  
+};
+
+struct VertexPosition
+{
+    float3 pos;
+    float3 normal;
+    float2 uv;
+};
+
+struct CameraView
+{
+    float3 camPos;
+    float3 camDir;
+};
+
+interface IVertexInterpolant
+{
+    float4 getVertexColor(int index);
+    int getVertexColorCount();
+    float2 getUV(int index);
+    int getUVCount();
+}
+
+interface IDisneyBRDFPattern
+{
+    __generic<TVertexInterpolant:IVertexInterpolant>
+    DisneyBRDFPattern evalPattern(
+        CameraView cam, 
+        VertexPosition vWorld,  
+        VertexPosition vObject, 
+        TVertexInterpolant interpolants);
+}
+
+struct StandardVertexInterpolant : IVertexInterpolant
+{
+    float4 getVertexColor(int index) { return float4(0.0); }
+    int getVertexColorCount() { return 0;}
+    float2 getUV(int index) { return float2(0.0); }
+    int getUVCount() {return 1; }
+};
+
+struct MaterialPattern1 : IDisneyBRDFPattern
+{
+    __generic<TVertexInterpolant:IVertexInterpolant>
+    DisneyBRDFPattern evalPattern(
+        CameraView cam, 
+        VertexPosition vWorld,  
+        VertexPosition vObject, 
+        TVertexInterpolant interpolants)
+    {
+        DisneyBRDFPattern rs;
+        rs.baseColor = float3(0.5);
+        rs.opacity = 1.0;
+        return rs;
+    }
+};
+
+__generic<TVertexInterpolant:IVertexInterpolant, TPattern : IDisneyBRDFPattern>
+float test(TVertexInterpolant vertInterps, TPattern pattern)
+{
+    CameraView cam;
+    VertexPosition vW, vO;
+    DisneyBRDFPattern rs = pattern.evalPattern(cam, vW, vO, vertInterps);    
+    return rs.baseColor.x;
+}
+[numthreads(4, 1, 1)]
+void computeMain(uint3 dispatchThreadID : SV_DispatchThreadID)
+{
+    StandardVertexInterpolant vertInterp;
+    MaterialPattern1 mp1;
+	float outVal = test<StandardVertexInterpolant, MaterialPattern1>(vertInterp, mp1);
+	outputBuffer[dispatchThreadID.x] = outVal;
+}
\ No newline at end of file
diff --git a/tests/compute/generic-interface-method.slang.expected.txt b/tests/compute/generic-interface-method.slang.expected.txt
new file mode 100644
index 000000000..e4e4c642a
--- /dev/null
+++ b/tests/compute/generic-interface-method.slang.expected.txt
@@ -0,0 +1,4 @@
+3F000000
+3F000000
+3F000000
+3F000000