Support mutable existential parameters. (#3836)

* Support mutable existential parameters.

* Update test.

1 files changed, 47 insertions, 0 deletions

diff --git a/tests/bugs/gh-3818.slang b/tests/bugs/gh-3818.slang
new file mode 100644
index 000000000..5b2c4db78
--- /dev/null
+++ b/tests/bugs/gh-3818.slang
@@ -0,0 +1,47 @@
+//TEST(compute):COMPARE_COMPUTE(filecheck-buffer=CHECK):-shaderobj -output-using-type
+
+interface IOperation
+{
+    [mutating]
+    void Store(float v);
+
+    float Load();
+};
+
+struct TOperationMax : IOperation
+{
+    float result;
+
+    [mutating]
+    void Store(float v)
+    {
+        result = v;
+    }
+
+    float Load()
+    {
+        return result;
+    }
+};
+
+float Run(inout IOperation op, float val)
+{
+    op.Store(val);
+    return op.Load();
+}
+
+//TEST_INPUT:ubuffer(data=[0 0 0 0], stride=4):out,name outputBuffer
+RWStructuredBuffer<float> outputBuffer;
+
+[numthreads(4, 1, 1)]
+[shader("compute")]
+void computeMain(uint3 dispatchThreadID : SV_DispatchThreadID)
+{
+    TOperationMax opMax;
+    opMax.result = 0.f;
+    float val = 2.f;
+    IOperation op = opMax;
+    float result = Run(op, val);
+    // CHECK: 2.0
+    outputBuffer[0] = result;
+}