[clang] [AMDGPU] Add builtin to test for constant memory (PR #209679)

[Krzysztof Drewniak via cfe-commits]

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@@ -356,6 +356,7 @@ def __builtin_amdgcn_fcmpf : AMDGPUBuiltin<"uint64_t(float, float, _Constant int
 //===----------------------------------------------------------------------===//
 def __builtin_amdgcn_is_shared : AMDGPUBuiltin<"bool(void const address_space<0> *)", [Const]>;
 def __builtin_amdgcn_is_private : AMDGPUBuiltin<"bool(void const address_space<0> *)", [Const]>;
+def __builtin_amdgcn_is_constant : AMDGPUBuiltin<"bool(void const address_space<0> *)", [Const]>;
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krzysz00 wrote:

I think because "constant" != "in addrspace(4)"

https://github.com/llvm/llvm-project/pull/209679