Don't initialize temp var for out parameters. (#6076)

1 files changed, 6 insertions, 4 deletions

diff --git a/source/slang/slang-ir-autodiff-rev.cpp b/source/slang/slang-ir-autodiff-rev.cpp
index 65ce69877..3237ba3b2 100644
--- a/source/slang/slang-ir-autodiff-rev.cpp
+++ b/source/slang/slang-ir-autodiff-rev.cpp
@@ -528,10 +528,12 @@ InstPair BackwardDiffTranscriber::transcribeFuncHeader(IRBuilder* inBuilder, IRF
                 // If primal parameter is mutable, we need to pass in a temp var.
                 auto tempVar = builder.emitVar(primalParamPtrType->getValueType());
 
-                // We also need to setup the initial value of the temp var, otherwise
-                // the temp var will be uninitialized which could cause undefined behavior
-                // in the primal function.
-                builder.emitStore(tempVar, primalArg);
+                // If the parameter is not a pure 'out' param, we also need to setup the initial
+                // value of the temp var, otherwise the temp var will be uninitialized which could
+                // cause undefined behavior in the primal function.
+                //
+                if (!as<IROutType>(primalParamType))
+                    builder.emitStore(tempVar, primalArg);
 
                 primalArgs.add(tempVar);
             }