gcc/libgomp/config/gcn/bar.c

/* Copyright (C) 2015-2020 Free Software Foundation, Inc.
   Contributed by Mentor Embedded.

   This file is part of the GNU Offloading and Multi Processing Library
   (libgomp).

   Libgomp is free software; you can redistribute it and/or modify it
   under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 3, or (at your option)
   any later version.

   Libgomp is distributed in the hope that it will be useful, but WITHOUT ANY
   WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
   FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
   more details.

   Under Section 7 of GPL version 3, you are granted additional
   permissions described in the GCC Runtime Library Exception, version
   3.1, as published by the Free Software Foundation.

   You should have received a copy of the GNU General Public License and
   a copy of the GCC Runtime Library Exception along with this program;
   see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
   <http://www.gnu.org/licenses/>.  */

/* This is an AMD GCN specific implementation of a barrier synchronization
   mechanism for libgomp.  This type is private to the library.  This
   implementation uses atomic instructions and s_barrier instruction.  It
   uses MEMMODEL_RELAXED here because barriers are within workgroups and
   therefore don't need to flush caches.  */

#include <limits.h>
#include "libgomp.h"


void
gomp_barrier_wait_end (gomp_barrier_t *bar, gomp_barrier_state_t state)
{
  if (__builtin_expect (state & BAR_WAS_LAST, 0))
    {
      /* Next time we'll be awaiting TOTAL threads again.  */
      bar->awaited = bar->total;
      __atomic_store_n (&bar->generation, bar->generation + BAR_INCR,
			MEMMODEL_RELAXED);
    }
  asm ("s_barrier" ::: "memory");
}

void
gomp_barrier_wait (gomp_barrier_t *bar)
{
  gomp_barrier_wait_end (bar, gomp_barrier_wait_start (bar));
}

/* Like gomp_barrier_wait, except that if the encountering thread
   is not the last one to hit the barrier, it returns immediately.
   The intended usage is that a thread which intends to gomp_barrier_destroy
   this barrier calls gomp_barrier_wait, while all other threads
   call gomp_barrier_wait_last.  When gomp_barrier_wait returns,
   the barrier can be safely destroyed.  */

void
gomp_barrier_wait_last (gomp_barrier_t *bar)
{
  /* Deferring to gomp_barrier_wait does not use the optimization opportunity
     allowed by the interface contract for all-but-last participants.  The
     original implementation in config/linux/bar.c handles this better.  */
  gomp_barrier_wait (bar);
}

void
gomp_team_barrier_wake (gomp_barrier_t *bar, int count)
{
  asm ("s_barrier" ::: "memory");
}

void
gomp_team_barrier_wait_end (gomp_barrier_t *bar, gomp_barrier_state_t state)
{
  unsigned int generation, gen;

  if (__builtin_expect (state & BAR_WAS_LAST, 0))
    {
      /* Next time we'll be awaiting TOTAL threads again.  */
      struct gomp_thread *thr = gomp_thread ();
      struct gomp_team *team = thr->ts.team;

      bar->awaited = bar->total;
      team->work_share_cancelled = 0;
      if (__builtin_expect (team->task_count, 0))
	{
	  gomp_barrier_handle_tasks (state);
	  state &= ~BAR_WAS_LAST;
	}
      else
	{
	  state &= ~BAR_CANCELLED;
	  state += BAR_INCR - BAR_WAS_LAST;
	  __atomic_store_n (&bar->generation, state, MEMMODEL_RELAXED);
	  asm ("s_barrier" ::: "memory");
	  return;
	}
    }

  generation = state;
  state &= ~BAR_CANCELLED;
  int retry = 100;
  do
    {
      if (retry-- == 0)
	{
	  /* It really shouldn't happen that barriers get out of sync, but
	     if they do then this will loop until they realign, so we need
	     to avoid an infinite loop where the thread just isn't there.  */
	  const char msg[] = ("Barrier sync failed (another thread died?);"
			      " aborting.");
	  write (2, msg, sizeof (msg)-1);
	  abort();
	}

      asm ("s_barrier" ::: "memory");
      gen = __atomic_load_n (&bar->generation, MEMMODEL_ACQUIRE);
      if (__builtin_expect (gen & BAR_TASK_PENDING, 0))
	{
	  gomp_barrier_handle_tasks (state);
	  gen = __atomic_load_n (&bar->generation, MEMMODEL_ACQUIRE);
	}
      generation |= gen & BAR_WAITING_FOR_TASK;
    }
  while (gen != state + BAR_INCR);
}

void
gomp_team_barrier_wait (gomp_barrier_t *bar)
{
  gomp_team_barrier_wait_end (bar, gomp_barrier_wait_start (bar));
}

void
gomp_team_barrier_wait_final (gomp_barrier_t *bar)
{
  gomp_barrier_state_t state = gomp_barrier_wait_final_start (bar);
  if (__builtin_expect (state & BAR_WAS_LAST, 0))
    bar->awaited_final = bar->total;
  gomp_team_barrier_wait_end (bar, state);
}

bool
gomp_team_barrier_wait_cancel_end (gomp_barrier_t *bar,
				   gomp_barrier_state_t state)
{
  unsigned int generation, gen;

  if (__builtin_expect (state & BAR_WAS_LAST, 0))
    {
      /* Next time we'll be awaiting TOTAL threads again.  */
      /* BAR_CANCELLED should never be set in state here, because
	 cancellation means that at least one of the threads has been
	 cancelled, thus on a cancellable barrier we should never see
	 all threads to arrive.  */
      struct gomp_thread *thr = gomp_thread ();
      struct gomp_team *team = thr->ts.team;

      bar->awaited = bar->total;
      team->work_share_cancelled = 0;
      if (__builtin_expect (team->task_count, 0))
	{
	  gomp_barrier_handle_tasks (state);
	  state &= ~BAR_WAS_LAST;
	}
      else
	{
	  state += BAR_INCR - BAR_WAS_LAST;
	  __atomic_store_n (&bar->generation, state, MEMMODEL_RELAXED);
	  asm ("s_barrier" ::: "memory");
	  return false;
	}
    }

  if (__builtin_expect (state & BAR_CANCELLED, 0))
    return true;

  generation = state;
  int retry = 100;
  do
    {
      if (retry-- == 0)
	{
	  /* It really shouldn't happen that barriers get out of sync, but
	     if they do then this will loop until they realign, so we need
	     to avoid an infinite loop where the thread just isn't there.  */
	  const char msg[] = ("Barrier sync failed (another thread died?);"
			      " aborting.");
	  write (2, msg, sizeof (msg)-1);
	  abort();
	}

      asm ("s_barrier" ::: "memory");
      gen = __atomic_load_n (&bar->generation, MEMMODEL_RELAXED);
      if (__builtin_expect (gen & BAR_CANCELLED, 0))
	return true;
      if (__builtin_expect (gen & BAR_TASK_PENDING, 0))
	{
	  gomp_barrier_handle_tasks (state);
	  gen = __atomic_load_n (&bar->generation, MEMMODEL_RELAXED);
	}
      generation |= gen & BAR_WAITING_FOR_TASK;
    }
  while (gen != state + BAR_INCR);

  return false;
}

bool
gomp_team_barrier_wait_cancel (gomp_barrier_t *bar)
{
  return gomp_team_barrier_wait_cancel_end (bar, gomp_barrier_wait_start (bar));
}

void
gomp_team_barrier_cancel (struct gomp_team *team)
{
  gomp_mutex_lock (&team->task_lock);
  if (team->barrier.generation & BAR_CANCELLED)
    {
      gomp_mutex_unlock (&team->task_lock);
      return;
    }
  team->barrier.generation |= BAR_CANCELLED;
  gomp_mutex_unlock (&team->task_lock);
  gomp_team_barrier_wake (&team->barrier, INT_MAX);
}