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From: "grg-webvisible+gcc.gnu.org at ai dot mit.edu"
 <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug libgomp/109452] New: omp_init_lock_with_hint() and
 omp_init_nest_lock_with_hint() are undefined
Date: Sat, 08 Apr 2023 20:34:02 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D109452

            Bug ID: 109452
           Summary: omp_init_lock_with_hint() and
                    omp_init_nest_lock_with_hint() are undefined
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libgomp
          Assignee: unassigned at gcc dot gnu.org
          Reporter: grg-webvisible+gcc.gnu.org at ai dot mit.edu
                CC: jakub at gcc dot gnu.org
  Target Milestone: ---

omp_init_lock_with_hint() and omp_init_nest_lock_with_hint() appear to be
declared but not defined:

    #include <omp.h>
    int main() {
        omp_lock_t lock;
        omp_init_lock_with_hint(&lock, omp_sync_hint_none);
    }

compiled with:

    gcc -fopenmp main.cpp

fails to link:

    In function `main':
    main.cpp:(.text+0x15): undefined reference to `omp_init_lock_with_hint'
    collect2: error: ld returned 1 exit status

on v12.1.0:

    GNU C++17 (GCC) version 12.1.0 (x86_64-pc-linux-gnu)
        compiled by GNU C version 12.1.0, GMP version 6.2.1, MPFR version
4.1.0, MPC version 1.2.1, isl version isl-0.24-GMP

Adding extra link options like -lgomp and -lpthread and -static does not he=
lp,
nor does using a different omp_sync_hint (and none of these should in fact
help).  Also confirmed with v11.3.0 and v9.5.0.

As a sanity check, the non-hint version works fine:

    #include <omp.h>
    int main() {
        omp_lock_t lock;
        omp_init_lock(&lock);
    }

These results are consistent with the observation that all of the init...lo=
ck
versions ({with and without hints} x {with and without nesting}) are declar=
ed
in omp.h, while only the versions without hints are defined in
gcc/libgomp/lock.c

omp_init_lock_with_hint() and omp_init_nest_lock_with_hint() are part of the
OpenMP 4.5 spec (Nov 2015), which is documented as being fully supported si=
nce
gcc v6.

The expedient solution of course would be to define in gcc/libgomp/lock.c t=
he
two init...with_hint functions to ignore the hint and call their correspond=
ing
unhinted init functions, e.g:

    void omp_init_lock_with_hint(omp_lock_t *lock, omp_sync_hint_t)
    {
        omp_init_lock(lock);
    }

    void omp_init_nest_lock_with_hint(omp_nest_lock_t *lock, omp_sync_hint_=
t)
    {
        omp_init_nest_lock(lock);
    }

Combined with the appropriate alias magic in the various
gcc/libgomp/config/*/lock.c files.

It would be particularly impressive to actually use the hints to make the l=
ocks
faster, but that's a larger project which probably deserves its own Bugz
entry...=