Eliminate empty struct on metal target (#6603)

* Eliminate empty struct on metal target

Close 6573.

We previously disabled the type legalization for ParameterBlock on
Metal, but Metal doesn't allow empty struct in the argument buffer
which is mapped from ParameterBlock, so we will need legalizeEmptyTypes
on Metal target.

* update test

* update function name

1 files changed, 33 insertions, 0 deletions

diff --git a/tests/metal/empty-struct-remove.slang b/tests/metal/empty-struct-remove.slang
new file mode 100644
index 000000000..2d9ee436b
--- /dev/null
+++ b/tests/metal/empty-struct-remove.slang
@@ -0,0 +1,33 @@
+
+//TEST:SIMPLE(filecheck=LIB):-target metallib -entry computeMain -stage compute -DMETAL
+//TEST:SIMPLE(filecheck=METAL):-target metal -entry computeMain -stage compute -DMETAL
+
+// METAL-NOT: struct emptyStruct
+struct emptyStruct
+{
+    void set(RWStructuredBuffer<int> buffer, int value) {buffer[0] = value;}
+}
+
+
+struct MyStruct
+{
+    RWStructuredBuffer<int> buffer;
+    int value;
+    void set()
+    {
+        e.set(buffer, value);
+    }
+    emptyStruct e;
+}
+
+ParameterBlock<MyStruct> param;
+
+// LIB: @computeMain
+[shader("compute")]
+[numthreads(1, 1, 1)]
+void computeMain(
+    uint tid: SV_DispatchThreadID,
+)
+{
+    param.set();
+}