Add support for `[PrimalSubstitute]` and `[PrimalSubstituteOf]`. (#2691)

* Add support for `[PrimalSubstitute]` and `[PrimalSubstituteOf]`.

* Fix

* Fix.

* Cleanup.

---------

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

1 files changed, 27 insertions, 0 deletions

diff --git a/tests/autodiff/primal-substitute.slang b/tests/autodiff/primal-substitute.slang
new file mode 100644
index 000000000..01f221f2a
--- /dev/null
+++ b/tests/autodiff/primal-substitute.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(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;
+
+float original(float x)
+{
+    return x * x;
+}
+
+[PrimalSubstituteOf(original)]
+[BackwardDifferentiable]
+float primalSubst(float x)
+{
+    return 2.0f * x * x;
+}
+
+[numthreads(1, 1, 1)]
+void computeMain(uint3 dispatchThreadID : SV_DispatchThreadID)
+{
+    var a = diffPair(3.0, 1.0);
+    __bwd_diff(original)(a, 1.0);
+    outputBuffer[0] = a.d;                                       // Expect: 12.0
+    outputBuffer[1] = __fwd_diff(original)(diffPair(3.0, 1.0)).p; // Expect: 18.0
+}