From 8b60459465252c7d47b58abf83fae2aa84915b03 Mon Sep 17 00:00:00 2001
From: Jakub Jelinek <jakub@redhat.com>
Date: Fri, 18 Dec 2020 21:43:20 +0100
Subject: [PATCH] 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.
---
 gcc/gimplify.c                       | 12 +++++++
 libgomp/testsuite/libgomp.c/task-6.c | 47 ++++++++++++++++++++++++++++
 2 files changed, 59 insertions(+)
 create mode 100644 libgomp/testsuite/libgomp.c/task-6.c

diff --git a/gcc/gimplify.c b/gcc/gimplify.c
index 54cb66bd1dd..87b6314e016 100644
--- a/gcc/gimplify.c
+++ b/gcc/gimplify.c
@@ -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)
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;
+}
-- 
2.30.2