[clang] [clang][HIP] Normalize __cdecl on abstract function types to the device default CC on amdgcnspirv (PR #210882)

[Arseniy Obolenskiy via cfe-commits]

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@@ -0,0 +1,30 @@
+// RUN: %clang_cc1 %s -fcuda-is-device -std=c++17 -triple spirv32 -aux-triple x86_64-pc-windows-msvc -fms-extensions -verify
+// RUN: %clang_cc1 %s -fcuda-is-device -std=c++17 -triple spirv64 -aux-triple x86_64-pc-windows-msvc -fms-extensions -verify
+// RUN: %clang_cc1 %s -fcuda-is-device -std=c++17 -triple spirv64-amd-amdhsa -aux-triple x86_64-pc-windows-msvc -fms-extensions -verify
+
+// __cdecl on an abstract function type must normalize to the device default
+// so std::function<void()> matches the library specialization keyed on
+// __cdecl on amdgcnspirv Windows.
+
+template <class T> struct classify_fn {
+  static constexpr int value = 0;
+};
+template <class R, class... A> struct classify_fn<R __cdecl(A...)> {
+  static constexpr int value = 1;
+};
+template <class R, class... A> struct classify_fn<R __vectorcall(A...)> {
+  static constexpr int value = 2;
+};
+
+// Unadorned function types resolve to the __cdecl specialization.
+static_assert(classify_fn<void()>::value == 1, "void() must match __cdecl");
+static_assert(classify_fn<int(double, char)>::value == 1,
+              "int(double,char) must match __cdecl");
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aobolensk wrote:

 Done, switched to the direct comparison you suggested

https://github.com/llvm/llvm-project/pull/210882