Bug 603546 – tc-has-openmp() function in toolchain-funcs.eclass fails to check for openmp support via libomp

• Status: RESOLVED INVALID
• Product: Gentoo Linux

[Description Amit Prakash Ambasta 2016-12-23 07:10:52 UTC]

tc-has-openmp is implemented as 

tc-has-openmp() {
	local base="${T}/test-tc-openmp"
	cat <<-EOF > "${base}.c"
	#include <omp.h>
	int main() {
		int nthreads, tid, ret = 0;
		#pragma omp parallel private(nthreads, tid)
		{
		tid = omp_get_thread_num();
		nthreads = omp_get_num_threads(); ret += tid + nthreads;
		}
		return ret;
	}
	EOF
	$(tc-getCC "$@") -fopenmp "${base}.c" -o "${base}" >&/dev/null
	local ret=$?
	rm -f "${base}"*
	return ${ret}
}

However, for llvm/clang openmp support is provided via libomp and the -fopenmp flag should be changed to -fopenmp=libomp.

The following implementation is recommended instead.

tc-has-openmp() {
	local base="${T}/test-tc-openmp"
	cat <<-EOF > "${base}.c"
	#include <omp.h>
	int main() {
		int nthreads, tid, ret = 0;
		#pragma omp parallel private(nthreads, tid)
		{
		tid = omp_get_thread_num();
		nthreads = omp_get_num_threads(); ret += tid + nthreads;
		}
		return ret;
	}
	EOF

	if tc-is-gcc; then
		$(tc-getCC "$@") -fopenmp "${base}.c" -o "${base}" >&/dev/null
	elif tc-is-clang; then
		$(tc-getCC "$@") -fopenmp=libomp "${base}.c" -o "${base}" >&/dev/null
	fi

	local ret=$?
	rm -f "${base}"*
	return ${ret}
}

[Comment 1 Amit Prakash Ambasta 2016-12-23 07:20:53 UTC]

Created attachment 457176 [details, diff]
libomp-llvm-openmp.patch

[Comment 2 Amit Prakash Ambasta 2016-12-23 08:41:33 UTC]

Sorry.. just verified that -fopenmp is sufficient