specialize witness tables when needed when specializing lookup_witness_table instruction. (shader-slang#376)

Author: csyonghe

source/slang/ir.cpp

@@ -4862,6 +4862,20 @@ namespace Slang
                             auto interfaceDeclRef = ((IRDeclRef*)lookupInst->interfaceType.usedValue)->declRef;
                             auto mangledName = getMangledNameForConformanceWitness(srcDeclRef, interfaceDeclRef);
                             witnessTables.TryGetValue(mangledName, witnessTable);
+                            
+                            if (!witnessTable)
+                            {
+                                // try specialize the witness table
+                                auto genDeclRef = srcDeclRef;
+                                genDeclRef.substitutions = createDefaultSubstitutions(module->session, genDeclRef.decl);
+                                auto genName = getMangledNameForConformanceWitness(genDeclRef, interfaceDeclRef);
+                                IRWitnessTable* genTable = nullptr;
+                                if (witnessTables.TryGetValue(genName, genTable))
+                                {
+                                    witnessTable = specializeWitnessTable(sharedContext, genTable, srcDeclRef, nullptr);
+                                    witnessTables.AddIfNotExists(witnessTable->mangledName, witnessTable);
+                                }
+                            }
                             if (witnessTable)
                             {
                                 lookupInst->replaceUsesWith(witnessTable);

source/slang/syntax.cpp

@@ -856,7 +856,12 @@ void Type::accept(IValVisitor* visitor, void* extra)
 
     Type* ErrorType::CreateCanonicalType()
     {
-        return  this;
+        return this;
+    }
+
+    RefPtr<Val> ErrorType::SubstituteImpl(SubstitutionSet /*subst*/, int* /*ioDiff*/)
+    {
+        return this;
     }
 
     int ErrorType::GetHashCode()

source/slang/type-defs.h

@@ -36,6 +36,7 @@ RAW(
 
 protected:
     virtual bool EqualsImpl(Type * type) override;
+    virtual RefPtr<Val> SubstituteImpl(SubstitutionSet subst, int* ioDiff) override;
     virtual Type* CreateCanonicalType() override;
     virtual int GetHashCode() override;
 )

tests/compute/int-generic.slang

@@ -0,0 +1,42 @@
+//TEST(compute):COMPARE_COMPUTE:-xslang -use-ir
+//TEST_INPUT:ubuffer(data=[0 0 0 0], stride=4):dxbinding(0),glbinding(0),out
+//TEST_INPUT:type Material<1,2>
+RWStructuredBuffer<int> outputBuffer;
+
+interface IBRDF
+{
+    int compute();
+};
+
+interface IMaterial
+{
+    associatedtype TBRDF : IBRDF;
+    TBRDF getBRDF();
+}
+
+struct BRDF<let A:int, let B:int> : IBRDF
+{
+    int c;
+    int compute()
+    {
+        return A+B;        
+    }
+};
+
+struct Material<let A:int, let B: int> : IMaterial
+{
+    typedef BRDF<A,B> TBRDF;
+    TBRDF getBRDF() { TBRDF a; a.c = 0; return a; }
+};
+
+type_param TMaterial : IMaterial;
+
+TMaterial material;
+
+[numthreads(1, 1, 1)]
+void computeMain(uint3 dispatchThreadID : SV_DispatchThreadID)
+{
+    TMaterial.TBRDF brdf = material.getBRDF();
+	int outVal = brdf.compute();
+	outputBuffer[dispatchThreadID.x] = outVal;
+}

tests/compute/int-generic.slang.expected.txt

@@ -0,0 +1 @@
+3