[clang] [Clang][AMDGPU] Add a new builtin type for buffer rsrc (PR #94830)

[Matt Arsenault via cfe-commits]

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+// REQUIRES: amdgpu-registered-target
+// RUN: %clang_cc1 -fsyntax-only -verify -triple amdgcn -Wno-unused-value %s
+
+void foo() {
+  int n = 100;
+  __buffer_rsrc_t v = 0; // expected-error {{cannot initialize a variable of type '__buffer_rsrc_t' with an rvalue of type 'int'}}
+  static_cast<__buffer_rsrc_t>(n); // expected-error {{static_cast from 'int' to '__buffer_rsrc_t' is not allowed}}
+  dynamic_cast<__buffer_rsrc_t>(n); // expected-error {{invalid target type '__buffer_rsrc_t' for dynamic_cast; target type must be a reference or pointer type to a defined class}}
+  reinterpret_cast<__buffer_rsrc_t>(n); // expected-error {{reinterpret_cast from 'int' to '__buffer_rsrc_t' is not allowed}}
+  int c(v); // expected-error {{cannot initialize a variable of type 'int' with an lvalue of type '__buffer_rsrc_t'}}
+}
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arsenm wrote:

Also test some c style casts to other pointer types 

https://github.com/llvm/llvm-project/pull/94830