[clang] [Clang][OpenCL][AMDGPU] Allow a kernel to call another kernel (PR #115821)

[Matt Arsenault via cfe-commits]

================
@@ -0,0 +1,43 @@
+// RUN: %clang_cc1 -triple amdgcn-unknown-unknown -emit-llvm -o - %s | FileCheck %s
+
+// CHECK: define dso_local amdgpu_kernel void @callee_kern({{.*}})
+__attribute__((noinline)) kernel void callee_kern(global int *A){
+  *A = 1;
+}
+
+__attribute__((noinline)) kernel void ext_callee_kern(global int *A);
+
+// CHECK: define dso_local void @callee_func({{.*}})
+__attribute__((noinline)) void callee_func(global int *A){
+  *A = 2;
+}
+
+// CHECK: define dso_local amdgpu_kernel void @caller_kern({{.*}})
+kernel void caller_kern(global int* A){
+  callee_kern(A);
+  // CHECK: tail call void @__clang_ocl_kern_imp_callee_kern({{.*}})
+  ext_callee_kern(A);
+  // CHECK: tail call void @__clang_ocl_kern_imp_ext_callee_kern({{.*}})
+  callee_func(A);
+  // CHECK: tail call void @callee_func({{.*}})
+
+}
+
+// CHECK: define dso_local void @__clang_ocl_kern_imp_callee_kern({{.*}})
+
+// CHECK: declare void @__clang_ocl_kern_imp_ext_callee_kern({{.*}})
+
+// CHECK: define dso_local void @caller_func({{.*}})
+void caller_func(global int* A){
+  callee_kern(A);
+  // CHECK: tail call void @__clang_ocl_kern_imp_callee_kern({{.*}}) #7
+  ext_callee_kern(A);
+  // CHECK: tail call void @__clang_ocl_kern_imp_ext_callee_kern({{.*}}) #8
+  callee_func(A);
+  // CHECK: tail call void @callee_func({{.*}})
+}
+
----------------
arsenm wrote:

I'd like to see more ABI attributes stressed, especially for aggregates. Test some structs of different sizes, and vectors. Also add another target runline to make sure we test both byref and byval 

https://github.com/llvm/llvm-project/pull/115821