[CUDA][SPIRV] Use OpenCLKernel CC for CUDA -> SPIRV

[dcastagna]

Summary

Select the OpenCLKernel calling convention for kernels when compiling
CUDA targeting SPIR-V.

In this way the generated LLVM IR will have a spir_kernel calling
convention that will be translated to an OpEntryPoint when converting
to SPIRV.

clang/lib/Sema/SemaType.cpp

static CallingConv getCCForDeclaratorChunk(
   // calling convention for OpenCL kernels.
   if (S.getLangOpts().OpenCL) {
     for (const ParsedAttr &AL : D.getDeclSpec().getAttributes()) {
       if (AL.getKind() == ParsedAttr::AT_OpenCLKernel) {
         CC = CC_OpenCLKernel;
         break;
       }
     }
+  } else if (S.getLangOpts().CUDA) {
+    // If we're compiling CUDA/HIP code and targeting SPIR-V we need to make
+    // sure the kernels will be marked with the right calling convention so that
+    // they will be visible by the APIs that ingest SPIR-V.
+    llvm::Triple Triple = S.Context.getTargetInfo().getTriple();
+    if (Triple.getArch() == llvm::Triple::spirv32 ||
+        Triple.getArch() == llvm::Triple::spirv64) {
+      for (const ParsedAttr &AL : D.getDeclSpec().getAttributes()) {
+        if (AL.getKind() == ParsedAttr::AT_CUDAGlobal) {
+          CC = CC_OpenCLKernel;
+          break;
+        }
+      }
+    }
   }
 
   return CC;
 }
 
 namespace {
   /// A simple notion of pointer kinds, which matches up with the various
   /// pointer declarators.

clang/test/CodeGenCUDASPIRV/kernel-cc.cu

+// RUN: %clang_cc1 -fcuda-is-device -triple spirv32 -o - -emit-llvm -x cuda %s  | FileCheck %s
+// RUN: %clang_cc1 -fcuda-is-device -triple spirv64 -o - -emit-llvm -x cuda %s  | FileCheck %s
+
+// Verifies that building CUDA targeting SPIR-V {32,64} generates LLVM IR with
+// spir_kernel attributes for kernel functions.
+
+// CHECK: define spir_kernel void @_Z6kernelv()
+
+__attribute__((global)) void kernel() { return; }