[Libomptarget] Add `cold` to KeepAlive attributes

[jhuber6]

Summary

This patch adds the cold attribute to the keepAlive functions in the
RTL. This dummy function exists to keep certain RTL calls alive without
them being optimized out, but it is never called and can be declared
cold. This also helps some erroneous remarks being given on this
function because it has weak linkage and cannot be made internal.

[tianshilei1992]

LG. Do we want a test that checks if the remark is not emitted?

[jhuber6]

In D117513#3249536, @tianshilei1992 wrote:

LG. Do we want a test that checks if the remark is not emitted?

I did a test locally and it resolved the issue, but it's not necessary because I already have a test that doesn't emit a remark if the cold attribute is present in OpenMPOpt's tests.

[tianshilei1992]

In D117513#3249539, @jhuber6 wrote:

In D117513#3249536, @tianshilei1992 wrote:

LG. Do we want a test that checks if the remark is not emitted?

I did a test locally and it resolved the issue, but it's not necessary because I already have a test that doesn't emit a remark if the cold attribute is present in OpenMPOpt's tests.

We don't have check line(s) in the test case?

[jhuber6]

In D117513#3249560, @tianshilei1992 wrote:

In D117513#3249539, @jhuber6 wrote:

In D117513#3249536, @tianshilei1992 wrote:

LG. Do we want a test that checks if the remark is not emitted?

I did a test locally and it resolved the issue, but it's not necessary because I already have a test that doesn't emit a remark if the cold attribute is present in OpenMPOpt's tests.

We don't have check line(s) in the test case?

It's covered by this line which basically tests internalization, which is what emits the remark this hides.

llvm/test/Transforms/OpenMP/single_threaded_execution.ll:; CHECK-NOT: [openmp-opt] Basic block @cold entry is executed by a single thread.

openmp/libomptarget/DeviceRTL/src/Utils.cpp

 #include "Mapping.h"
 
 #pragma omp declare target
 
 using namespace _OMP;
 
 namespace _OMP {
 /// Helper to keep code alive without introducing a performance penalty.
-__attribute__((used, retain, weak, optnone)) void keepAlive() {
+__attribute__((used, retain, weak, optnone, cold)) void keepAlive() {
   __kmpc_get_hardware_thread_id_in_block();
   __kmpc_get_hardware_num_threads_in_block();
   __kmpc_get_warp_size();
   __kmpc_barrier_simple_spmd(nullptr, 0);
   __kmpc_barrier_simple_generic(nullptr, 0);
 }
 } // namespace _OMP
 

openmp/libomptarget/deviceRTLs/common/src/support.cu

#include "common/generated_microtask_cases.gen"
   default:
     printf("Too many arguments in kmp_invoke_microtask, aborting execution.\n");
     __builtin_trap();
   }
 }
 
 namespace _OMP {
 /// Helper to keep code alive without introducing a performance penalty.
-__attribute__((used, retain, weak, optnone)) void keepAlive() {
+__attribute__((used, retain, weak, optnone, cold)) void keepAlive() {
   __kmpc_get_hardware_thread_id_in_block();
   __kmpc_get_hardware_num_threads_in_block();
   __kmpc_get_warp_size();
   __kmpc_barrier_simple_spmd(nullptr, 0);
   __kmpc_barrier_simple_generic(nullptr, 0);
 }
 } // namespace _OMP
 
 #pragma omp end declare target