Make `__BuiltinFloatingPointType` conform to `IDifferentiable`. (#2499)

1 files changed, 10 insertions, 1 deletions

diff --git a/source/slang/slang-lower-to-ir.cpp b/source/slang/slang-lower-to-ir.cpp
index f8d8282d8..12a9f73e6 100644
--- a/source/slang/slang-lower-to-ir.cpp
+++ b/source/slang/slang-lower-to-ir.cpp
@@ -1349,6 +1349,7 @@ struct ValLoweringVisitor : ValVisitor<ValLoweringVisitor, LoweredValInfo, Lower
         // The base (subToMid) will turn into a value with
         // witness-table type.
         IRInst* baseWitnessTable = lowerSimpleVal(context, val->subToMid);
+        IRInst* midToSup = nullptr;
 
         // The next step should map to an interface requirement
         // that is itself an interface conformance, so the result
@@ -1366,7 +1367,6 @@ struct ValLoweringVisitor : ValVisitor<ValLoweringVisitor, LoweredValInfo, Lower
         // produce transitive witnesses in shapes that will cuase us
         // problems here.
         //
-        IRInst* midToSup = lowerSimpleVal(context, val->midToSup);
 
         if (!baseWitnessTable)
         {
@@ -1380,6 +1380,15 @@ struct ValLoweringVisitor : ValVisitor<ValLoweringVisitor, LoweredValInfo, Lower
             return LoweredValInfo::simple(midToSup);
         }
 
+        if (auto declaredMidToSup = as<DeclaredSubtypeWitness>(val->midToSup))
+        {
+            midToSup = getInterfaceRequirementKey(context, declaredMidToSup->declRef.decl);
+        }
+        else
+        {
+            midToSup = lowerSimpleVal(context, val->midToSup);
+        }
+
         return LoweredValInfo::simple(getBuilder()->emitLookupInterfaceMethodInst(
             getBuilder()->getWitnessTableType(lowerType(context, val->sup)),
             baseWitnessTable,