[libomptarget] omp_get_default_device doesn't returning host device in the case of OMP_TARGET_OFFLOAD=disabled

[ye-luo]

spec 6.0 says
Support for the disabled value is implementation defined. If an implementation supports it, the behavior is as if the only device is the host device.

Based on the above spec, when the environment variable OMP_TARGET_OFFLOAD=disabled is set, the expected return from omp_get_default_device should agree with omp_get_initial_device which reports the host device. This is not the current case

reproducer.cpp

#include <omp.h>
#include <iostream>

int main(){
        std::cout << "num_of_device = " << omp_get_num_devices() << std::endl;
        std::cout << "initial_device = " << omp_get_initial_device() << std::endl;
        std::cout << "default_device = " << omp_get_default_device() << std::endl;

        int a[8];
#pragma omp target enter data map(to: a[:8])
        int* b = (int *)omp_get_mapped_ptr(a, omp_get_default_device());

        std::cout << "a_ptr = " << a << " b_ptr = " << b << std::endl;
}

compile and run

yeluo@epyc-server:~/temp$ clang++ -fopenmp --offload-arch=gfx906 main.cpp
yeluo@epyc-server:~/temp$ OMP_TARGET_OFFLOAD=disabled ./a.out 
num_of_device = 1
initial_device = 1
default_device = 0
a_ptr = 0x7ffdd63e4440 b_ptr = 0
yeluo@epyc-server:~/temp$ OMP_TARGET_OFFLOAD=mandatory ./a.out 
num_of_device = 1
initial_device = 1
default_device = 0
a_ptr = 0x7fff3355e020 b_ptr = 0x721958200000

default_device doesn't behave as expected.