Make tuple types work in autodiff. (#4923)

1 files changed, 17 insertions, 3 deletions

diff --git a/source/slang/slang-lower-to-ir.cpp b/source/slang/slang-lower-to-ir.cpp
index 31427e616..87199734a 100644
--- a/source/slang/slang-lower-to-ir.cpp
+++ b/source/slang/slang-lower-to-ir.cpp
@@ -5401,6 +5401,8 @@ struct LValueExprLoweringVisitor : ExprLoweringVisitorBase<LValueExprLoweringVis
             }
         };
 
+        LoweredValInfo result;
+
         // As required by the implementation of 'assign' and as a small
         // optimization, we will detect if the base expression has also lowered
         // into a swizzle and only return a single swizzle instead of nested
@@ -5435,7 +5437,7 @@ struct LValueExprLoweringVisitor : ExprLoweringVisitorBase<LValueExprLoweringVis
                 swizzledLValue->elementIndices);
 
             context->shared->extValues.add(swizzledLValue);
-            return LoweredValInfo::swizzledLValue(swizzledLValue);
+            result = LoweredValInfo::swizzledLValue(swizzledLValue);
         }
         else if(loweredBase.flavor == LoweredValInfo::Flavor::SwizzledMatrixLValue)
         {
@@ -5455,7 +5457,7 @@ struct LValueExprLoweringVisitor : ExprLoweringVisitorBase<LValueExprLoweringVis
                 swizzledLValue->elementCoords);
 
             context->shared->extValues.add(swizzledLValue);
-            return LoweredValInfo::swizzledMatrixLValue(swizzledLValue);
+            result = LoweredValInfo::swizzledMatrixLValue(swizzledLValue);
         }
         else
         {
@@ -5464,8 +5466,20 @@ struct LValueExprLoweringVisitor : ExprLoweringVisitorBase<LValueExprLoweringVis
             swizzledLValue->base = loweredBase;
             swizzledLValue->elementIndices = expr->elementIndices;
             context->shared->extValues.add(swizzledLValue);
-            return LoweredValInfo::swizzledLValue(swizzledLValue);
+            result = LoweredValInfo::swizzledLValue(swizzledLValue);
+        }
+
+        // For a one-element swizzle on a tuple, we can just return the pointer to the member
+        // instead of a SwizzledLValue because they can't follow the same folding logic as
+        // vectors and matrices.
+        //
+        bool shouldUseSimpleLVal = elementCount == 1 && as<TupleType>(expr->base->type) != nullptr;
+        if (shouldUseSimpleLVal)
+        {
+            auto addr = getAddress(context, result, expr->loc);
+            return LoweredValInfo::ptr(addr);
         }
+        return result;
     }
 };