From 5e1974e8cad3396a8c4bedfd63c1ad31b82ec8eb Mon Sep 17 00:00:00 2001
From: Yong He <yonghe@outlook.com>
Date: Tue, 30 May 2023 10:41:34 -0700
Subject: Fix derivative signature bug in checkDerivativeAttribute. (#2905)

---
 source/slang/slang-check-decl.cpp                  |  3 ++-
 .../reverse-inout-param-custom-derivative.slang    | 28 ++++++++++++++++++++++
 ...nout-param-custom-derivative.slang.expected.txt |  2 ++
 3 files changed, 32 insertions(+), 1 deletion(-)
 create mode 100644 tests/autodiff/reverse-inout-param-custom-derivative.slang
 create mode 100644 tests/autodiff/reverse-inout-param-custom-derivative.slang.expected.txt

diff --git a/source/slang/slang-check-decl.cpp b/source/slang/slang-check-decl.cpp
index c7a955f06..4e2f146a1 100644
--- a/source/slang/slang-check-decl.cpp
+++ b/source/slang/slang-check-decl.cpp
@@ -7027,7 +7027,8 @@ namespace Slang
         List<Expr*> imaginaryArguments;
         auto isOutParam = [&](ParamDecl* param)
         {
-            return param->findModifier<OutModifier>() != nullptr && param->findModifier<InModifier>() == nullptr;
+            return param->findModifier<OutModifier>() != nullptr
+                && param->findModifier<InModifier>() == nullptr && param->findModifier<InOutModifier>() == nullptr;
         };
 
         for (auto param : originalFuncDecl->getParameters())
diff --git a/tests/autodiff/reverse-inout-param-custom-derivative.slang b/tests/autodiff/reverse-inout-param-custom-derivative.slang
new file mode 100644
index 000000000..8769a33c7
--- /dev/null
+++ b/tests/autodiff/reverse-inout-param-custom-derivative.slang
@@ -0,0 +1,28 @@
+//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], stride=4):out,name=outputBuffer
+RWStructuredBuffer<float> outputBuffer;
+
+float rng(inout int state, float x)
+{
+    return state + x;
+}
+
+[BackwardDerivativeOf(rng)]
+void rng_bwd(int inState, inout DifferentialPair<float> x, float dOut)
+{
+    x = diffPair(x.p, (float)inState + dOut - 1.0);
+}
+
+[numthreads(1, 1, 1)]
+void computeMain(uint3 dispatchThreadID : SV_DispatchThreadID)
+{
+    var x = diffPair(2.0, 1.0);
+
+    __bwd_diff(rng)(4, x, 3.0);
+
+    outputBuffer[0] = x.d; // should be 6
+
+}
diff --git a/tests/autodiff/reverse-inout-param-custom-derivative.slang.expected.txt b/tests/autodiff/reverse-inout-param-custom-derivative.slang.expected.txt
new file mode 100644
index 000000000..bb8f4137d
--- /dev/null
+++ b/tests/autodiff/reverse-inout-param-custom-derivative.slang.expected.txt
@@ -0,0 +1,2 @@
+type: float
+6.000000
-- 
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