Support `IDifferentiablePtrType` (#5031)

* initial diff-ref-type interface

* Initial support for `IDifferentiablePtrType`

* Fix unused vars

* More tests + fix switch case fallthrough.

* Update slang-ir-autodiff.cpp

* Update diff-ptr-type-loop.slang

* Add optimization to allow more complex pair types

* Update slang-ir-autodiff-primal-hoist.cpp

* Update diff-ptr-type-loop.slang

* Update slang-ir-autodiff-primal-hoist.cpp

* More fixes to address reviews

* Update slang-check-expr.cpp

* Optimizations + rename `differentiableRefInterfaceType` -> `differentiablePtrInterfaceType`

* Move pair logic to ir-builder, unify the type dictionaries.

---------

Co-authored-by: Yong He <yonghe@outlook.com>

1 files changed, 25 insertions, 7 deletions

diff --git a/source/slang/slang-check-expr.cpp b/source/slang/slang-check-expr.cpp
index 8f24ec5b0..5233008fd 100644
--- a/source/slang/slang-check-expr.cpp
+++ b/source/slang/slang-check-expr.cpp
@@ -1131,7 +1131,8 @@ namespace Slang
         {
             if (auto builtinRequirement = declRefType->getDeclRef().getDecl()->findModifier<BuiltinRequirementModifier>())
             {
-                if (builtinRequirement->kind == BuiltinRequirementKind::DifferentialType)
+                if (builtinRequirement->kind == BuiltinRequirementKind::DifferentialType
+                    || builtinRequirement->kind == BuiltinRequirementKind::DifferentialPtrType)
                 {
                     // We are trying to get differential type from a differential type.
                     // The result is itself.
@@ -1139,7 +1140,10 @@ namespace Slang
                 }
             }
             type = resolveType(type);
-            if (const auto witness = as<SubtypeWitness>(tryGetInterfaceConformanceWitness(type, builder->getDifferentiableInterfaceType())))
+            auto witness = as<SubtypeWitness>(tryGetInterfaceConformanceWitness(type, builder->getDifferentiableInterfaceType()));
+            if (!witness)
+                witness = as<SubtypeWitness>(tryGetInterfaceConformanceWitness(type, builder->getDifferentiableRefInterfaceType()));
+            if (witness)
             {
                 auto diffTypeLookupResult = lookUpMember(
                     getASTBuilder(),
@@ -1367,6 +1371,13 @@ namespace Slang
             {
                 addDifferentiableTypeToDiffTypeRegistry((DeclRefType*)type, subtypeWitness);
             }
+
+            if (auto subtypeWitness = as<SubtypeWitness>(
+                tryGetInterfaceConformanceWitness(type, getASTBuilder()->getDifferentiableRefInterfaceType())))
+            {
+                addDifferentiableTypeToDiffTypeRegistry((DeclRefType*)type, subtypeWitness);
+            }
+
             if (auto aggTypeDeclRef = declRefType->getDeclRef().as<AggTypeDecl>())
             {
                 foreachDirectOrExtensionMemberOfType<InheritanceDecl>(this, aggTypeDeclRef, [&](DeclRef<InheritanceDecl> member)
@@ -2899,18 +2910,25 @@ namespace Slang
                 return m_astBuilder->getExpandType(diffPairEachType, makeArrayViewSingle(primalType));
             }
         }
+
         // Get a reference to the builtin 'IDifferentiable' interface
         auto differentiableInterface = getASTBuilder()->getDifferentiableInterfaceType();
+        auto differentiableRefInterface = getASTBuilder()->getDifferentiableRefInterfaceType();
 
-        auto conformanceWitness = as<Witness>(isSubtype(primalType, differentiableInterface, IsSubTypeOptions::None));
         // Check if the provided type inherits from IDifferentiable.
         // If not, return the original type.
-        if (conformanceWitness)
+        if (auto conformanceWitness = isTypeDifferentiable(primalType))
         {
-            return m_astBuilder->getDifferentialPairType(primalType, conformanceWitness);
+            if (conformanceWitness->getSup() == differentiableInterface)
+            {
+                return m_astBuilder->getDifferentialPairType(primalType, conformanceWitness);
+            }
+            else if (conformanceWitness->getSup() == differentiableRefInterface)
+            {
+                return m_astBuilder->getDifferentialPtrPairType(primalType, conformanceWitness);
+            }
         }
-        else
-            return primalType;
+        return primalType;
     }
 
     Type* SemanticsVisitor::getForwardDiffFuncType(FuncType* originalType)