Treat user defined backward derivative function as non differentiable. (#2650)

Co-authored-by: Yong He <yhe@nvidia.com>

2 files changed, 33 insertions, 0 deletions

diff --git a/tests/autodiff/backward-diff-check.slang b/tests/autodiff/backward-diff-check.slang
new file mode 100644
index 000000000..2718f31f1
--- /dev/null
+++ b/tests/autodiff/backward-diff-check.slang
@@ -0,0 +1,27 @@
+//TEST(compute):COMPARE_COMPUTE_EX:-slang -compute -shaderobj -output-using-type
+//TEST(compute, vulkan):COMPARE_COMPUTE_EX:-vk -compute -shaderobj -output-using-type
+
+//TEST_INPUT:ubuffer(data=[0 0 0 0 0], stride=4):out,name=outputBuffer
+RWStructuredBuffer<float> outputBuffer;
+
+typedef DifferentialPair<float> dpfloat;
+typedef float.Differential dfloat;
+
+[BackwardDifferentiable]
+float test()
+{
+    return 2.0f;
+}
+
+float noDiffFunc(float x) { return x; }
+[BackwardDerivativeOf(test)]
+void d_test(float dOut)
+{
+    outputBuffer[0] = noDiffFunc(dOut);
+}
+
+[numthreads(1, 1, 1)]
+void computeMain(uint3 dispatchThreadID : SV_DispatchThreadID)
+{
+    __bwd_diff(test)(3.0f);
+}
diff --git a/tests/autodiff/backward-diff-check.slang.expected.txt b/tests/autodiff/backward-diff-check.slang.expected.txt
new file mode 100644
index 000000000..72bbdbbcd
--- /dev/null
+++ b/tests/autodiff/backward-diff-check.slang.expected.txt
@@ -0,0 +1,6 @@
+type: float
+3.000000
+0.000000
+0.000000
+0.000000
+0.000000