Fix lowering of associated types in generic interfaces (#6600)

* Fix lowering of associated types in generic interfaces.

* Update diff-assoctype-generic-interface.slang

* Fix-up lowering of differentiable witnesses for implicit ops

* Update slang-ir-autodiff-transcriber-base.cpp

* Fix issue with differentiating type-packs

1 files changed, 21 insertions, 7 deletions

diff --git a/source/slang/slang-check-expr.cpp b/source/slang/slang-check-expr.cpp
index b730069b6..2f91a6a77 100644
--- a/source/slang/slang-check-expr.cpp
+++ b/source/slang/slang-check-expr.cpp
@@ -1405,14 +1405,12 @@ Type* SemanticsVisitor::getDifferentialType(ASTBuilder* builder, Type* type, Sou
     return result;
 }
 
-void SemanticsVisitor::addDifferentiableTypeToDiffTypeRegistry(
-    DeclRefType* type,
-    SubtypeWitness* witness)
+void SemanticsVisitor::addDifferentiableTypeToDiffTypeRegistry(Type* type, SubtypeWitness* witness)
 {
     SLANG_RELEASE_ASSERT(m_parentDifferentiableAttr);
     if (witness)
     {
-        m_parentDifferentiableAttr->addType(type->getDeclRef(), witness);
+        m_parentDifferentiableAttr->addType(type, witness);
     }
 }
 
@@ -1468,14 +1466,14 @@ void SemanticsVisitor::maybeRegisterDifferentiableTypeImplRecursive(ASTBuilder*
                 type,
                 getASTBuilder()->getDifferentiableInterfaceType())))
         {
-            addDifferentiableTypeToDiffTypeRegistry((DeclRefType*)type, subtypeWitness);
+            addDifferentiableTypeToDiffTypeRegistry(type, subtypeWitness);
         }
 
         if (auto subtypeWitness = as<SubtypeWitness>(tryGetInterfaceConformanceWitness(
                 type,
                 getASTBuilder()->getDifferentiableRefInterfaceType())))
         {
-            addDifferentiableTypeToDiffTypeRegistry((DeclRefType*)type, subtypeWitness);
+            addDifferentiableTypeToDiffTypeRegistry(type, subtypeWitness);
         }
 
         if (auto aggTypeDeclRef = declRefType->getDeclRef().as<AggTypeDecl>())
@@ -1515,6 +1513,15 @@ void SemanticsVisitor::maybeRegisterDifferentiableTypeImplRecursive(ASTBuilder*
             maybeRegisterDifferentiableTypeImplRecursive(builder, typePack->getElementType(i));
         return;
     }
+
+    // General check for types that may not be decl-ref-type, but still have some conformance to
+    // IDifferentiable/IDifferentiablePtrType
+    if (auto subtypeWitness = as<SubtypeWitness>(tryGetInterfaceConformanceWitness(
+            type,
+            getASTBuilder()->getDifferentiableInterfaceType())))
+    {
+        addDifferentiableTypeToDiffTypeRegistry(type, subtypeWitness);
+    }
 }
 
 
@@ -4846,7 +4853,14 @@ Expr* SemanticsVisitor::checkBaseForMemberExpr(
     auto baseExpr = inBaseExpr;
     baseExpr = CheckTerm(baseExpr);
 
-    return maybeInsertImplicitOpForMemberBase(baseExpr, checkBaseContext, outNeedDeref);
+    auto resultBaseExpr =
+        maybeInsertImplicitOpForMemberBase(baseExpr, checkBaseContext, outNeedDeref);
+
+    // We might want to register differentiability on any implicit ops that we add in.
+    if (this->m_parentFunc && this->m_parentFunc->findModifier<DifferentiableAttribute>())
+        maybeRegisterDifferentiableType(getASTBuilder(), resultBaseExpr->type.type);
+
+    return resultBaseExpr;
 }
 
 Expr* SemanticsVisitor::checkGeneralMemberLookupExpr(MemberExpr* expr, Type* baseType)