[SYCL][NATIVECPU] Fix assert in MS name mangler (#11103)

This PR prevents the MS name mangler to assert on the unhandled
`CC_OpenCLKernel` calling convention which can end up in the AST when
targeting NativeCPU on Windows - see attached test case that triggers
the assert. This assert is also triggered on a number of e2e tests on
NativeCPU. This patch handles the CC_OpenCLKernel convention currently
only for NativeCPU and the usual error is raised for other targets as
before.

Author: uwedolinsky

clang/lib/AST/MicrosoftMangle.cpp

@@ -2906,6 +2906,17 @@ void MicrosoftCXXNameMangler::mangleCallingConvention(CallingConv CC) {
       else
         Out << "w";
       break;
+    case CC_OpenCLKernel:
+      // This can occur on the SYCl NativeCPU device
+      // where device code is compiled with the same
+      // target triple (eg for Windows) as host code.
+      // FIXME: 1.) provide mangling if needed
+      //        2.) check if other conventions need to be handled.
+      if (!getASTContext().getLangOpts().SYCLIsNativeCPU)
+        // Currently we only allow this convention in
+        // SYCLNativeCPU and raise the usual error otherwise.
+        llvm_unreachable("Unsupported CC for mangling");
+      break;
   }
 }
 void MicrosoftCXXNameMangler::mangleCallingConvention(const FunctionType *T) {

clang/test/CodeGenSYCL/native_cpu_mangling.cpp

@@ -0,0 +1,18 @@
+// This test ensures the native-cpu device generates the expected kernel names,
+// and that the MS mangler doesn't assert on the code below.
+
+// RUN: %clang_cc1 -triple x86_64-pc-windows-msvc   -aux-triple x86_64-pc-windows-msvc   -I %S/Inputs -fsycl-is-device -fsycl-is-native-cpu -emit-llvm -o - -x c++ %s | FileCheck %s
+// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -aux-triple x86_64-unknown-linux-gnu -I %S/Inputs -fsycl-is-device -fsycl-is-native-cpu -emit-llvm -o - -x c++ %s | FileCheck %s
+// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -aux-triple x86_64-pc-windows-msvc   -I %S/Inputs -fsycl-is-device -fsycl-is-native-cpu -emit-llvm -o - -x c++ %s | FileCheck %s
+// RUN: %clang_cc1 -triple x86_64-pc-windows-msvc   -aux-triple x86_64-unknown-linux-gnu -I %S/Inputs -fsycl-is-device -fsycl-is-native-cpu -emit-llvm -o - -x c++ %s | FileCheck %s
+// Todo: check other cpus
+
+#include "sycl.hpp"
+
+struct name1;
+
+void test(sycl::handler &h) {
+  h.parallel_for_work_group<name1>(sycl::range<1>(2),sycl::range<1>(1), [=](sycl::group<1> G) {});
+}    
+
+// CHECK: void @_ZTS5name1(