7 files changed, 97 insertions, 0 deletions

diff --git a/source/slang/slang-ast-expr.h b/source/slang/slang-ast-expr.h
index c07f7f5b9..f9b8831f1 100644
--- a/source/slang/slang-ast-expr.h
+++ b/source/slang/slang-ast-expr.h
@@ -544,6 +544,13 @@ class OpenRefExpr : public Expr
     Expr* innerExpr = nullptr;
 };
 
+class DetachExpr : public Expr
+{
+    SLANG_AST_CLASS(DetachExpr)
+
+    Expr* inner = nullptr;
+};
+
     /// Base class for higher-order function application
     /// Eg: foo(fn) where fn is a function expression.
     ///
@@ -563,6 +570,7 @@ class DifferentiateExpr : public HigherOrderInvokeExpr
 {
     SLANG_ABSTRACT_AST_CLASS(DifferentiateExpr)
 };
+
     /// An expression of the form `__fwd_diff(fn)` to access the 
     /// forward-mode derivative version of the function `fn`
     ///
diff --git a/source/slang/slang-check-conversion.cpp b/source/slang/slang-check-conversion.cpp
index c135ada8d..85040dc55 100644
--- a/source/slang/slang-check-conversion.cpp
+++ b/source/slang/slang-check-conversion.cpp
@@ -498,6 +498,27 @@ namespace Slang
             toInitializerListExpr->type = QualType(toType);
             toInitializerListExpr->args = coercedArgs;
 
+            // Wrap initalizer list args if we're creating a non-differentiable struct within a 
+            // differentiable function.
+            // 
+            if (auto func = getParentFuncOfVisitor())
+            {
+                if (func->findModifier<DifferentiableAttribute>() && 
+                    !isTypeDifferentiable(toType))
+                {
+                    for (auto &arg : toInitializerListExpr->args)
+                    {
+                        if (isTypeDifferentiable(arg->type.type))
+                        {
+                            auto detachedArg = m_astBuilder->create<DetachExpr>();
+                            detachedArg->inner = arg;
+                            detachedArg->type = arg->type;
+                            arg = detachedArg;
+                        }
+                    }
+                }
+            }
+
             *outToExpr = toInitializerListExpr;
         }
 
diff --git a/source/slang/slang-check-expr.cpp b/source/slang/slang-check-expr.cpp
index 4d36299bb..3072c3257 100644
--- a/source/slang/slang-check-expr.cpp
+++ b/source/slang/slang-check-expr.cpp
@@ -3242,6 +3242,13 @@ namespace Slang
         return expr;
     }
 
+    Expr* SemanticsExprVisitor::visitDetachExpr(DetachExpr* expr)
+    {
+        expr->inner = CheckTerm(expr->inner);
+        expr->type = expr->inner->type;
+        return expr;
+    }
+
 
     static bool _isSizeOfType(Type* type)
     {
diff --git a/source/slang/slang-check-impl.h b/source/slang/slang-check-impl.h
index 82ac8de59..f997abc57 100644
--- a/source/slang/slang-check-impl.h
+++ b/source/slang/slang-check-impl.h
@@ -2806,6 +2806,8 @@ namespace Slang
 
         Expr* visitDefaultConstructExpr(DefaultConstructExpr* expr);
 
+        Expr* visitDetachExpr(DetachExpr* expr);
+
         Expr* visitSPIRVAsmExpr(SPIRVAsmExpr*);
 
             /// Perform semantic checking on a `modifier` that is being applied to the given `type`
diff --git a/source/slang/slang-lower-to-ir.cpp b/source/slang/slang-lower-to-ir.cpp
index 02c4fae68..b9d7a898f 100644
--- a/source/slang/slang-lower-to-ir.cpp
+++ b/source/slang/slang-lower-to-ir.cpp
@@ -3929,6 +3929,16 @@ struct ExprLoweringVisitorBase : public ExprVisitor<Derived, LoweredValInfo>
                 baseVal.val));
     }
 
+    LoweredValInfo visitDetachExpr(DetachExpr* expr)
+    {
+        auto baseVal = lowerRValueExpr(context, expr->inner);
+
+        return LoweredValInfo::simple(
+            getBuilder()->emitDetachDerivative(
+                lowerType(context, expr->type),
+                getSimpleVal(context, baseVal)));
+    }
+
     LoweredValInfo visitPrimalSubstituteExpr(PrimalSubstituteExpr* expr)
     {
         auto baseVal = lowerSubExpr(expr->baseFunction);
diff --git a/tests/autodiff/field-extract-of-make-struct.slang b/tests/autodiff/field-extract-of-make-struct.slang
new file mode 100644
index 000000000..1cf2b40c4
--- /dev/null
+++ b/tests/autodiff/field-extract-of-make-struct.slang
@@ -0,0 +1,43 @@
+//TEST(compute):COMPARE_COMPUTE_EX:-slang -compute -shaderobj -output-using-type
+//TEST(compute, vulkan):COMPARE_COMPUTE_EX:-vk -compute -shaderobj -output-using-type
+//TEST(compute):COMPARE_COMPUTE_EX:-cpu -compute -output-using-type -shaderobj
+
+//TEST_INPUT:ubuffer(data=[0 0 0 0 0], stride=4):out,name=outputBuffer
+RWStructuredBuffer<float> outputBuffer;
+
+// This test checks to ensure that expressions of the form FieldExtract(MakeStruct(...))
+// are handled correctly in the presence of differentiation. 
+// Such expressions are often optimized out, and the non-differentiability of the struct 
+// type can be accidentally overlooked.
+//
+
+typedef DifferentialPair<float> dpfloat;
+typedef float.Differential dfloat;
+
+struct Data
+{
+    [PreferRecompute]
+    __init(float tin)
+    {
+        this.t = tin;
+    }
+    float t;
+};
+
+[BackwardDifferentiable]
+float test_make_struct(float y)
+{
+    Data d = { y };
+    return d.t;
+}
+
+[numthreads(1, 1, 1)]
+void computeMain(uint3 dispatchThreadID : SV_DispatchThreadID)
+{
+    {
+        dpfloat dpa = dpfloat(1.0, 0.0);
+
+        bwd_diff(test_make_struct)(dpa, 1.0f);
+        outputBuffer[0] = dpa.d; // Expect: 0.0
+    }
+}
\ No newline at end of file
diff --git a/tests/autodiff/field-extract-of-make-struct.slang.expected.txt b/tests/autodiff/field-extract-of-make-struct.slang.expected.txt
new file mode 100644
index 000000000..e070cf84d
--- /dev/null
+++ b/tests/autodiff/field-extract-of-make-struct.slang.expected.txt
@@ -0,0 +1,6 @@
+type: float
+0.000000
+0.000000
+0.000000
+0.000000
+0.000000