[Bug libgomp/66715] New: libgomp.oacc-c/../libgomp.oacc-c-c++-common/data-{2,3}.c exec fails -Ofast

["vries at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66715

            Bug ID: 66715
           Summary: libgomp.oacc-c/../libgomp.oacc-c-c++-common/data-{2,3}
                    .c exec fails -Ofast
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libgomp
          Assignee: unassigned at gcc dot gnu.org
          Reporter: vries at gcc dot gnu.org
                CC: jakub at gcc dot gnu.org
  Target Milestone: ---

With gomp-4_0-branch, when running target-libgomp testsuite with
--target_board=unix/-Ofast, we have:

c.exp:
...
FAIL: libgomp.oacc-c/../libgomp.oacc-c-c++-common/data-2.c
-DACC_DEVICE_TYPE_host_nonshm=1 -DACC_MEM_SHARED=0 execution test
FAIL: libgomp.oacc-c/../libgomp.oacc-c-c++-common/data-3.c
-DACC_DEVICE_TYPE_host_nonshm=1 -DACC_MEM_SHARED=0 execution test
FAIL: libgomp.oacc-c/../libgomp.oacc-c-c++-common/data-2.c
-DACC_DEVICE_TYPE_host=1 -DACC_MEM_SHARED=1 execution test
FAIL: libgomp.oacc-c/../libgomp.oacc-c-c++-common/data-3.c
-DACC_DEVICE_TYPE_host=1 -DACC_MEM_SHARED=1 execution test
...

c++.exp:
...
FAIL: libgomp.oacc-c++/../libgomp.oacc-c-c++-common/data-2.c
-DACC_DEVICE_TYPE_host_nonshm=1 -DACC_MEM_SHARED=0 execution test
FAIL: libgomp.oacc-c++/../libgomp.oacc-c-c++-common/data-3.c
-DACC_DEVICE_TYPE_host_nonshm=1 -DACC_MEM_SHARED=0 execution test
FAIL: libgomp.oacc-c++/../libgomp.oacc-c-c++-common/data-2.c
-DACC_DEVICE_TYPE_host=1 -DACC_MEM_SHARED=1 execution test
FAIL: libgomp.oacc-c++/../libgomp.oacc-c-c++-common/data-3.c
-DACC_DEVICE_TYPE_host=1 -DACC_MEM_SHARED=1 execution test
...

failure mode:
...
(gdb) up
#2  0x000000000040347f in main (argc=<optimized out>, argv=<optimized out>)
    at
src/libgomp/testsuite/libgomp.oacc-c/../libgomp.oacc-c-c++-common/data-2.c:40
40              abort ();
(gdb) l
35      #pragma acc wait
36      
37        for (i = 0; i < N; i++)
38          {
39            if (a[i] != 3.0)
40              abort ();
41      
42            if (b[i] != 3.0)
43              abort ();
44          }
...