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* [gcc r9-9402] openmp: Don't optimize shared to firstprivate on task with depend clause
@ 2021-04-20 23:30 Jakub Jelinek
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From: Jakub Jelinek @ 2021-04-20 23:30 UTC (permalink / raw)
To: gcc-cvs
https://gcc.gnu.org/g:8313557e2714f710247372caa8b473e292ebff42
commit r9-9402-g8313557e2714f710247372caa8b473e292ebff42
Author: Jakub Jelinek <jakub@redhat.com>
Date: Fri Dec 18 21:43:20 2020 +0100
openmp: Don't optimize shared to firstprivate on task with depend clause
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.
(cherry picked from commit 99ddd36e800a24fcb744a14ff9adabb0a7ef72c8)
Diff:
---
gcc/gimplify.c | 12 +++++++++
libgomp/testsuite/libgomp.c/task-6.c | 47 ++++++++++++++++++++++++++++++++++++
2 files changed, 59 insertions(+)
diff --git a/gcc/gimplify.c b/gcc/gimplify.c
index e103e76b466..8c30910d90d 100644
--- a/gcc/gimplify.c
+++ b/gcc/gimplify.c
@@ -211,6 +211,7 @@ struct gimplify_omp_ctx
bool distribute;
bool target_firstprivatize_array_bases;
bool add_safelen1;
+ bool has_depend;
int defaultmap[4];
};
@@ -8886,6 +8887,8 @@ 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:
@@ -9503,6 +9506,11 @@ 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;
@@ -9750,6 +9758,10 @@ 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)
diff --git a/libgomp/testsuite/libgomp.c/task-6.c b/libgomp/testsuite/libgomp.c/task-6.c
new file mode 100644
index 00000000000..e5fc758d283
--- /dev/null
+++ b/libgomp/testsuite/libgomp.c/task-6.c
@@ -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;
+}
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