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/* Copyright (C) 2005-2022 Free Software Foundation, Inc.
Contributed by Richard Henderson <rth@redhat.com>.
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 file contains routines for managing work-share iteration, both
for loops and sections. */
#include "libgomp.h"
#include <stdlib.h>
/* This function implements the STATIC scheduling method. The caller should
iterate *pstart <= x < *pend. Return zero if there are more iterations
to perform; nonzero if not. Return less than 0 if this thread had
received the absolutely last iteration. */
int
gomp_iter_static_next (long *pstart, long *pend)
{
struct gomp_thread *thr = gomp_thread ();
struct gomp_team *team = thr->ts.team;
struct gomp_work_share *ws = thr->ts.work_share;
unsigned long nthreads = team ? team->nthreads : 1;
if (thr->ts.static_trip == -1)
return -1;
/* Quick test for degenerate teams and orphaned constructs. */
if (nthreads == 1)
{
*pstart = ws->next;
*pend = ws->end;
thr->ts.static_trip = -1;
return ws->next == ws->end;
}
/* We interpret chunk_size zero as "unspecified", which means that we
should break up the iterations such that each thread makes only one
trip through the outer loop. */
if (ws->chunk_size == 0)
{
unsigned long n, q, i, t;
unsigned long s0, e0;
long s, e;
if (thr->ts.static_trip > 0)
return 1;
/* Compute the total number of iterations. */
s = ws->incr + (ws->incr > 0 ? -1 : 1);
n = (ws->end - ws->next + s) / ws->incr;
i = thr->ts.team_id;
/* Compute the "zero-based" start and end points. That is, as
if the loop began at zero and incremented by one. */
q = n / nthreads;
t = n % nthreads;
if (i < t)
{
t = 0;
q++;
}
s0 = q * i + t;
e0 = s0 + q;
/* Notice when no iterations allocated for this thread. */
if (s0 >= e0)
{
thr->ts.static_trip = 1;
return 1;
}
/* Transform these to the actual start and end numbers. */
s = (long)s0 * ws->incr + ws->next;
e = (long)e0 * ws->incr + ws->next;
*pstart = s;
*pend = e;
thr->ts.static_trip = (e0 == n ? -1 : 1);
return 0;
}
else
{
unsigned long n, s0, e0, i, c;
long s, e;
/* Otherwise, each thread gets exactly chunk_size iterations
(if available) each time through the loop. */
s = ws->incr + (ws->incr > 0 ? -1 : 1);
n = (ws->end - ws->next + s) / ws->incr;
i = thr->ts.team_id;
c = ws->chunk_size;
/* Initial guess is a C sized chunk positioned nthreads iterations
in, offset by our thread number. */
s0 = (thr->ts.static_trip * nthreads + i) * c;
e0 = s0 + c;
/* Detect overflow. */
if (s0 >= n)
return 1;
if (e0 > n)
e0 = n;
/* Transform these to the actual start and end numbers. */
s = (long)s0 * ws->incr + ws->next;
e = (long)e0 * ws->incr + ws->next;
*pstart = s;
*pend = e;
if (e0 == n)
thr->ts.static_trip = -1;
else
thr->ts.static_trip++;
return 0;
}
}
/* This function implements the DYNAMIC scheduling method. Arguments are
as for gomp_iter_static_next. This function must be called with ws->lock
held. */
bool
gomp_iter_dynamic_next_locked (long *pstart, long *pend)
{
struct gomp_thread *thr = gomp_thread ();
struct gomp_work_share *ws = thr->ts.work_share;
long start, end, chunk, left;
start = ws->next;
if (start == ws->end)
return false;
chunk = ws->chunk_size;
left = ws->end - start;
if (ws->incr < 0)
{
if (chunk < left)
chunk = left;
}
else
{
if (chunk > left)
chunk = left;
}
end = start + chunk;
ws->next = end;
*pstart = start;
*pend = end;
return true;
}
#ifdef HAVE_SYNC_BUILTINS
/* Similar, but doesn't require the lock held, and uses compare-and-swap
instead. Note that the only memory value that changes is ws->next. */
bool
gomp_iter_dynamic_next (long *pstart, long *pend)
{
struct gomp_thread *thr = gomp_thread ();
struct gomp_work_share *ws = thr->ts.work_share;
long start, end, nend, chunk, incr;
end = ws->end;
incr = ws->incr;
chunk = ws->chunk_size;
if (__builtin_expect (ws->mode, 1))
{
long tmp = __sync_fetch_and_add (&ws->next, chunk);
if (incr > 0)
{
if (tmp >= end)
return false;
nend = tmp + chunk;
if (nend > end)
nend = end;
*pstart = tmp;
*pend = nend;
return true;
}
else
{
if (tmp <= end)
return false;
nend = tmp + chunk;
if (nend < end)
nend = end;
*pstart = tmp;
*pend = nend;
return true;
}
}
start = __atomic_load_n (&ws->next, MEMMODEL_RELAXED);
while (1)
{
long left = end - start;
long tmp;
if (start == end)
return false;
if (incr < 0)
{
if (chunk < left)
chunk = left;
}
else
{
if (chunk > left)
chunk = left;
}
nend = start + chunk;
tmp = __sync_val_compare_and_swap (&ws->next, start, nend);
if (__builtin_expect (tmp == start, 1))
break;
start = tmp;
}
*pstart = start;
*pend = nend;
return true;
}
#endif /* HAVE_SYNC_BUILTINS */
/* This function implements the GUIDED scheduling method. Arguments are
as for gomp_iter_static_next. This function must be called with the
work share lock held. */
bool
gomp_iter_guided_next_locked (long *pstart, long *pend)
{
struct gomp_thread *thr = gomp_thread ();
struct gomp_work_share *ws = thr->ts.work_share;
struct gomp_team *team = thr->ts.team;
unsigned long nthreads = team ? team->nthreads : 1;
unsigned long n, q;
long start, end;
if (ws->next == ws->end)
return false;
start = ws->next;
n = (ws->end - start) / ws->incr;
q = (n + nthreads - 1) / nthreads;
if (q < ws->chunk_size)
q = ws->chunk_size;
if (q <= n)
end = start + q * ws->incr;
else
end = ws->end;
ws->next = end;
*pstart = start;
*pend = end;
return true;
}
#ifdef HAVE_SYNC_BUILTINS
/* Similar, but doesn't require the lock held, and uses compare-and-swap
instead. Note that the only memory value that changes is ws->next. */
bool
gomp_iter_guided_next (long *pstart, long *pend)
{
struct gomp_thread *thr = gomp_thread ();
struct gomp_work_share *ws = thr->ts.work_share;
struct gomp_team *team = thr->ts.team;
unsigned long nthreads = team ? team->nthreads : 1;
long start, end, nend, incr;
unsigned long chunk_size;
start = __atomic_load_n (&ws->next, MEMMODEL_RELAXED);
end = ws->end;
incr = ws->incr;
chunk_size = ws->chunk_size;
while (1)
{
unsigned long n, q;
long tmp;
if (start == end)
return false;
n = (end - start) / incr;
q = (n + nthreads - 1) / nthreads;
if (q < chunk_size)
q = chunk_size;
if (__builtin_expect (q <= n, 1))
nend = start + q * incr;
else
nend = end;
tmp = __sync_val_compare_and_swap (&ws->next, start, nend);
if (__builtin_expect (tmp == start, 1))
break;
start = tmp;
}
*pstart = start;
*pend = nend;
return true;
}
#endif /* HAVE_SYNC_BUILTINS */
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