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

[Jakub Jelinek via Gcc-patches]

Hi!

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.

Bootstrapped/regtested on x86_64-linux and i686-linux, committed to trunk
so far.

2020-12-18  Jakub Jelinek  <ja...@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.jj   2020-11-26 01:14:47.537081889 +0100
+++ gcc/gimplify.c      2020-12-18 17:31:53.746888168 +0100
@@ -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,
              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_tre
            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
                  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)
--- libgomp/testsuite/libgomp.c/task-6.c.jj     2020-12-18 16:55:34.422690908 
+0100
+++ libgomp/testsuite/libgomp.c/task-6.c        2020-12-18 17:22:02.568615365 
+0100
@@ -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;
+}


        Jakub