[clang] [llvm] [AMDGPU][clang][CodeGen][opt] Add late-resolved feature identifying predicates (PR #134016)

[Alex Voicu via llvm-commits]

================
@@ -4920,6 +4920,116 @@ If no address spaces names are provided, all address spaces are fenced.
   __builtin_amdgcn_fence(__ATOMIC_SEQ_CST, "workgroup", "local")
   __builtin_amdgcn_fence(__ATOMIC_SEQ_CST, "workgroup", "local", "global")
 
+__builtin_amdgcn_processor_is and __builtin_amdgcn_is_invocable
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+``__builtin_amdgcn_processor_is`` and ``__builtin_amdgcn_is_invocable`` provide
+a functional mechanism for programatically querying:
+
+* the identity of the current target processor;
+* the capability of the current target processor to invoke a particular builtin.
+
+**Syntax**:
+
+.. code-block:: c
+
+  // When used as the predicate for a control structure
+  bool __builtin_amdgcn_processor_is(const char*);
+  bool __builtin_amdgcn_is_invocable(builtin_name);
+  // Otherwise
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AlexVlx wrote:

Type, when "observable", is always `void`. So e.g. `decltype(__builtin_amdgcn_processor_is(...)), sizeof(__builtin_amdgcn_processor_is(...)), auto x = __builtin_amdgcn_processor_is(...); decltype(x)` would always be `void` / errors. I will pick up the other two Qs in a more thorough reply.

https://github.com/llvm/llvm-project/pull/134016