Fix DCE for calls to functions that have associations (#6272)

* Fix DCE for calls to functions that have associations

* Update slang-ir-util.cpp

* Update slang-ir-util.cpp

1 files changed, 35 insertions, 0 deletions

diff --git a/tests/autodiff/custom-diff-empty-func.slang b/tests/autodiff/custom-diff-empty-func.slang
new file mode 100644
index 000000000..c566d9e19
--- /dev/null
+++ b/tests/autodiff/custom-diff-empty-func.slang
@@ -0,0 +1,35 @@
+//TEST(compute):COMPARE_COMPUTE_EX(filecheck-buffer=CHECK):-slang -compute -shaderobj -output-using-type -g0
+
+//TEST_INPUT:ubuffer(data=[0 0 0 0], stride=4):out,name=outputBuffer
+RWStructuredBuffer<float> outputBuffer;
+
+void foo_bwd(float a, inout DifferentialPair<float> dpx)
+{
+    outputBuffer[2] = 2.f;
+}
+
+[Differentiable, BackwardDerivative(foo_bwd)]
+void foo(no_diff float a, float x)
+{ }
+
+[Differentiable]
+float outerFunc(no_diff float a, float x)
+{
+    foo(a, x);
+    return 1.f;
+}
+
+[numthreads(1, 1, 1)]
+[shader("compute")]
+void computeMain(uint3 dispatchThreadID: SV_DispatchThreadID)
+{
+    float a = 10.0;
+    DifferentialPair<float> dpx = DifferentialPair<float>(4.f, 1.f);
+    bwd_diff(outerFunc)(a, dpx, 1.0);
+    
+    // CHECK: type: float
+    // CHECK: 0.0
+    // CHECK: 0.0
+    // CHECK: 2.0
+    // CHECK: 0.0
+}
\ No newline at end of file