[gcc/devel/omp/gcc-11] openmp: Fix OpenMP expansion of scope with non-fallthrugh body [PR102415]

[Tobias Burnus <burnus@gcc.gnu.org>]

https://gcc.gnu.org/g:147d6b7dda411f3fcfe585b967ecaf0f5b75551b

commit 147d6b7dda411f3fcfe585b967ecaf0f5b75551b
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Wed Sep 22 09:57:46 2021 +0200

    openmp: Fix OpenMP expansion of scope with non-fallthrugh body [PR102415]
    
    I've used function for omp single expansion also for omp scope.  That is
    mostly ok, but as the testcase shows, there is one important difference.
    The omp single expansion always has a fallthru body, because it during
    omp lowering expands the body as if wrapped in an if to simulate that
    one thread runs the body and others wait (unless nowait) until it completes
    and continue.  omp scope is invoked by all threads and so if the body
    is non-fallthru, the barrier (unless nowait) at the end will not be reached
    by any of the threads.
    
    The following patch fixes that by handling the case where cfg pass optimizes
    away the exit bb of it gracefully.
    
    2021-09-22  Jakub Jelinek  <jakub@redhat.com>
    
            PR middle-end/102415
            * omp-expand.c (expand_omp_single): If region->exit is NULL,
            assert region->entry is GIMPLE_OMP_SCOPE region and return.
    
            * c-c++-common/gomp/scope-3.c: New test.
    
    (cherry picked from commit c4432b2776aeeffee9125bf87ff937e4a8907bbd)

Diff:
---
 gcc/ChangeLog.omp                         |  9 +++++++++
 gcc/omp-expand.c                          | 10 ++++++++--
 gcc/testsuite/ChangeLog.omp               |  8 ++++++++
 gcc/testsuite/c-c++-common/gomp/scope-3.c | 21 +++++++++++++++++++++
 4 files changed, 46 insertions(+), 2 deletions(-)

diff --git a/gcc/ChangeLog.omp b/gcc/ChangeLog.omp
index a84e0411304..e62ff21c278 100644
--- a/gcc/ChangeLog.omp
+++ b/gcc/ChangeLog.omp
@@ -1,3 +1,12 @@
+2021-09-22  Tobias Burnus  <tobias@codesourcery.com>
+
+	Backported from master:
+	2021-09-22  Jakub Jelinek  <jakub@redhat.com>
+
+	PR middle-end/102415
+	* omp-expand.c (expand_omp_single): If region->exit is NULL,
+	assert region->entry is GIMPLE_OMP_SCOPE region and return.
+
 2021-09-22  Tobias Burnus  <tobias@codesourcery.com>
 
 	Backported from master:
diff --git a/gcc/omp-expand.c b/gcc/omp-expand.c
index fd86786270f..b87921b166a 100644
--- a/gcc/omp-expand.c
+++ b/gcc/omp-expand.c
@@ -8483,11 +8483,17 @@ expand_omp_single (struct omp_region *region)
   exit_bb = region->exit;
 
   si = gsi_last_nondebug_bb (entry_bb);
-  gcc_assert (gimple_code (gsi_stmt (si)) == GIMPLE_OMP_SINGLE
-	      || gimple_code (gsi_stmt (si)) == GIMPLE_OMP_SCOPE);
+  enum gimple_code code = gimple_code (gsi_stmt (si));
+  gcc_assert (code == GIMPLE_OMP_SINGLE || code == GIMPLE_OMP_SCOPE);
   gsi_remove (&si, true);
   single_succ_edge (entry_bb)->flags = EDGE_FALLTHRU;
 
+  if (exit_bb == NULL)
+    {
+      gcc_assert (code == GIMPLE_OMP_SCOPE);
+      return;
+    }
+
   si = gsi_last_nondebug_bb (exit_bb);
   if (!gimple_omp_return_nowait_p (gsi_stmt (si)))
     {
diff --git a/gcc/testsuite/ChangeLog.omp b/gcc/testsuite/ChangeLog.omp
index 3138d9893a9..48a9f531afe 100644
--- a/gcc/testsuite/ChangeLog.omp
+++ b/gcc/testsuite/ChangeLog.omp
@@ -1,3 +1,11 @@
+2021-09-22  Tobias Burnus  <tobias@codesourcery.com>
+
+	Backported from master:
+	2021-09-22  Jakub Jelinek  <jakub@redhat.com>
+
+	PR middle-end/102415
+	* c-c++-common/gomp/scope-3.c: New test.
+
 2021-09-22  Tobias Burnus  <tobias@codesourcery.com>
 
 	Backported from master:
diff --git a/gcc/testsuite/c-c++-common/gomp/scope-3.c b/gcc/testsuite/c-c++-common/gomp/scope-3.c
new file mode 100644
index 00000000000..78bb1a3ccb9
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/gomp/scope-3.c
@@ -0,0 +1,21 @@
+/* PR middle-end/102415 */
+
+extern
+#ifdef __cplusplus
+"C"
+#endif
+void abort ();
+
+void
+foo (void)
+{
+  #pragma omp scope nowait
+  abort ();
+}
+
+void
+bar (void)
+{
+  #pragma omp scope
+  abort ();
+}