[clang] [HLSL] Parameter modifier parsing and AST (PR #72139)

[Justin Bogner via cfe-commits]

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+// RUN: %clang_cc1 -triple dxil-pc-shadermodel6.6-library %s -verify
+void fn(in out float f); // #fn
+
+// expected-error@#fn2{{duplicate parameter modifier 'in'}}
+// expected-note@#fn2{{conflicting attribute is here}}
+void fn2(in in float f); // #fn2
+
+// expected-error@#fn3{{duplicate parameter modifier 'out'}}
+// expected-note@#fn3{{conflicting attribute is here}}
+void fn3(out out float f); // #fn3
+
+// expected-error@#fn4{{duplicate parameter modifier 'in'}}
+// expected-error@#fn4{{duplicate parameter modifier 'out'}}
+// expected-note@#fn4{{conflicting attribute is here}}
+// expected-note@#fn4{{conflicting attribute is here}}
+void fn4(inout in out float f); // #fn4
+
+// expected-error@#fn5{{duplicate parameter modifier 'in'}}
+// expected-note@#fn5{{conflicting attribute is here}}
+void fn5(inout in float f); // #fn5
+
+// expected-error@#fn6{{duplicate parameter modifier 'out'}}
+// expected-note@#fn6{{conflicting attribute is here}}
+void fn6(inout out float f); // #fn6
+
+// expected-error@#fn-def{{conflicting parameter qualifier 'out' on parameter 'f'}}
+// expected-note@#fn{{previously declared as 'inout' here}}
+void fn(out float f) { // #fn-def
+  f = 2;
+}
+
+// Overload resolution failure.
+void fn(in float f); // #fn-in
+
+void failOverloadResolution() {
+  float f = 1.0;
+  fn(f); // expected-error{{call to 'fn' is ambiguous}}
+  // expected-note@#fn-def{{candidate function}}
+  // expected-note@#fn-in{{candidate function}}
+}
+
+// No errors on these scenarios.
+
+// Alternating `inout` and `in out` spellings between declaration and
+// definitions is fine since they have the same semantic meaning.
+void fn7(inout float f);
+void fn7(in out float f) {}
+
+void fn8(in out float f);
+void fn8(inout float f) {}
+
+// These two declare two different functions (although calling them will be
+// ambiguous). This is equivalent to declaring a functiion that takes a
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bogner wrote:

Typo. s/functiion/function/

https://github.com/llvm/llvm-project/pull/72139