[clang] [HLSL] Add testing for space parameter on global constants (PR #106782)

[Joshua Batista via cfe-commits]

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@@ -1,5 +1,24 @@
 // RUN: %clang_cc1 -triple dxil-pc-shadermodel6.3-library -x hlsl -o - -fsyntax-only %s -verify
 
+// valid
+cbuffer cbuf {
+    RWBuffer<int> r : register(u0, space0);
+}
+
+cbuffer cbuf2 {
+    struct x {
+        // expected-error at +1 {{'register' attribute only applies to cbuffer/tbuffer and external global variables}}
+        RWBuffer<int> E : register(u2, space3);
+    };
+}
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bob80905 wrote:

I thought to add this to show why the `!isDeclaredWithinCOrTBuffer` call is necessary. It prevents the second diagnostic about the space parameter from being emitted. I don't believe there is a case like this that uses the space parameter.

https://github.com/llvm/llvm-project/pull/106782