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openmp: Don't optimize shared to firstprivate on task with depend clause

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The attached testcase is miscompiled, because we optimize shared clauses
to firstprivate when task body can't modify the variable even when the
task has depend clause.  That is wrong, because firstprivate means the
variable will be copied immediately when the task is created, while with
depend clause some other task might change it later before the dependencies
are satisfied and the task should observe the value only after the change.

2020-12-18  Jakub Jelinek  <jakub@redhat.com>

	* gimplify.c (struct gimplify_omp_ctx): Add has_depend member.
	(gimplify_scan_omp_clauses): Set it to true if OMP_CLAUSE_DEPEND
	appears on OMP_TASK.
	(gimplify_adjust_omp_clauses_1, gimplify_adjust_omp_clauses): Force
	GOVD_WRITTEN on shared variables if task construct has depend clause.

	* testsuite/libgomp.c/task-6.c: New test.
This commit is contained in:
Jakub Jelinek 2020-12-18 21:43:20 +01:00
parent bfb37fa4dd
commit 8b60459465
2 changed files with 59 additions and 0 deletions
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12
gcc/gimplify.c
View File

@ -231,6 +231,7 @@ struct gimplify_omp_ctx
bool target_firstprivatize_array_bases;
bool add_safelen1;
bool order_concurrent;
bool has_depend;
int defaultmap[4];
};
@ -9497,6 +9498,8 @@ gimplify_scan_omp_clauses (tree *list_p, gimple_seq *pre_p,
remove = true;
break;
}
if (code == OMP_TASK)
ctx->has_depend = true;
break;
case OMP_CLAUSE_TO:
@ -10207,6 +10210,11 @@ gimplify_adjust_omp_clauses_1 (splay_tree_node n, void *data)
return 0;
}
code = OMP_CLAUSE_SHARED;
/* Don't optimize shared into firstprivate for read-only vars
on tasks with depend clause, we shouldn't try to copy them
until the dependencies are satisfied. */
if (gimplify_omp_ctxp->has_depend)
flags |= GOVD_WRITTEN;
}
else if (flags & GOVD_PRIVATE)
code = OMP_CLAUSE_PRIVATE;
@ -10494,6 +10502,10 @@ gimplify_adjust_omp_clauses (gimple_seq *pre_p, gimple_seq body, tree *list_p,
OMP_CLAUSE_SET_CODE (c, OMP_CLAUSE_PRIVATE);
OMP_CLAUSE_PRIVATE_DEBUG (c) = 1;
}
if (OMP_CLAUSE_CODE (c) == OMP_CLAUSE_SHARED
&& ctx->has_depend
&& DECL_P (decl))
n->value |= GOVD_WRITTEN;
if (OMP_CLAUSE_CODE (c) == OMP_CLAUSE_SHARED
&& (n->value & GOVD_WRITTEN) == 0
&& DECL_P (decl)

47
libgomp/testsuite/libgomp.c/task-6.c Normal file
View File

@ -0,0 +1,47 @@
#include <stdlib.h>
#include <unistd.h>
int
main ()
{
int x = 0, y = 0;
#pragma omp parallel shared(x, y)
#pragma omp master
{
#pragma omp task depend(out:y) shared(x, y)
{
sleep (1);
x = 1;
y = 1;
}
#pragma omp task depend(inout:y) shared(x, y)
{
if (x != 1 || y != 1)
abort ();
y++;
}
}
if (x != 1 || y != 2)
abort ();
x = 0;
y = 0;
#pragma omp parallel
#pragma omp master
{
#pragma omp task depend(out:y)
{
sleep (1);
x = 1;
y = 1;
}
#pragma omp task depend(inout:y)
{
if (x != 1 || y != 1)
abort ();
y++;
}
}
if (x != 1 || y != 2)
abort ();
return 0;
}