Correct IR generation for no-diff pointer type (#5976)

* Correct IR generation for no-diff pointer type

Close #5805 

There is an issue on checking whether a pointer type parameter
is no_diff, we should first check whether this parameter is
an Attribute type first, then check the data type.

In the back-propagate pass, for the pointer type parameter, we should
load this parameter to a temp variable, then pass it to the primal
function call. Otherwise, the temp variable will no be initialized,
which will cause the following calculation wrong.

1 files changed, 14 insertions, 5 deletions

diff --git a/source/slang/slang-ir-autodiff.cpp b/source/slang/slang-ir-autodiff.cpp
index 5c05b0811..4edd8eabe 100644
--- a/source/slang/slang-ir-autodiff.cpp
+++ b/source/slang/slang-ir-autodiff.cpp
@@ -126,13 +126,22 @@ static IRInst* _getDiffTypeWitnessFromPairType(
 
 bool isNoDiffType(IRType* paramType)
 {
-    while (auto ptrType = as<IRPtrTypeBase>(paramType))
-        paramType = ptrType->getValueType();
-    while (auto attrType = as<IRAttributedType>(paramType))
+    while (paramType)
     {
-        if (attrType->findAttr<IRNoDiffAttr>())
+        if (auto attrType = as<IRAttributedType>(paramType))
         {
-            return true;
+            if (attrType->findAttr<IRNoDiffAttr>())
+                return true;
+
+            paramType = attrType->getBaseType();
+        }
+        else if (auto ptrType = as<IRPtrTypeBase>(paramType))
+        {
+            paramType = ptrType->getValueType();
+        }
+        else
+        {
+            return false;
         }
     }
     return false;