Hi!

On 2021-07-19T10:46:35+0200, I wrote:
> | On 7/16/21 11:42 AM, Thomas Schwinge wrote:
> |> On 2021-07-09T17:11:25-0600, Martin Sebor via Gcc-patches <gcc-patches@gcc.gnu.org> wrote:
> |>> The attached tweak avoids the new -Warray-bounds instances when
> |>> building libatomic for arm. Christophe confirms it resolves
> |>> the problem (thank you!)
> |>
> |> As Abid has just reported in
> |> <https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101374#c16>, similar
> |> problem with GCN target libgomp build:
> |>
> |>      In function ‘gcn_thrs’,
> |>          inlined from ‘gomp_thread’ at [...]/source-gcc/libgomp/libgomp.h:803:10,
> |>          inlined from ‘GOMP_barrier’ at [...]/source-gcc/libgomp/barrier.c:34:29:
> |>      [...]/source-gcc/libgomp/libgomp.h:792:10: error: array subscript 0 is outside array bounds of ‘__lds struct gomp_thread * __lds[0]’ [-Werror=array-bounds]
> |>        792 |   return *thrs;
> |>            |          ^~~~~
> |>
> |>      gcc/config/gcn/gcn.h:  c_register_addr_space ("__lds", ADDR_SPACE_LDS);                   \
> |>
> |>      libgomp/libgomp.h-static inline struct gomp_thread *gcn_thrs (void)
> |>      libgomp/libgomp.h-{
> |>      libgomp/libgomp.h-  /* The value is at the bottom of LDS.  */
> |>      libgomp/libgomp.h:  struct gomp_thread * __lds *thrs = (struct gomp_thread * __lds *)4;
> |>      libgomp/libgomp.h-  return *thrs;
> |>      libgomp/libgomp.h-}
> |>
> |> ..., plus a few more.  Work-around:
> |>
> |>         struct gomp_thread * __lds *thrs = (struct gomp_thread * __lds *)4;
> |>      +# pragma GCC diagnostic push
> |>      +# pragma GCC diagnostic ignored "-Warray-bounds"
> |>         return *thrs;
> |>      +# pragma GCC diagnostic pop
> |>
> |> ..., but it's a bit tedious to add that in all that the other places,
> |> too.
>
> Wasn't so bad after all; a lot of duplicates due to 'libgomp.h'.  I've
> thus pushed "[gcn] Work-around libgomp 'error: array subscript 0 is
> outside array bounds of ‘__lds struct gomp_thread * __lds[0]’
> [-Werror=array-bounds]' [PR101484]" to master branch in commit
> 9f2bc5077debef2b046b6c10d38591ac324ad8b5, see attached.

As I should find, these '#pragma GCC diagnostic [...]' directives cause
some code generation changes (that seems unexpected, problematic!).
(Martin, any idea?  Might be a pre-existing problem, of course.)  This
results in a lot (ten thousands) of 'GCN team arena exhausted' run-time
diagnostics, also leading to a few FAILs:

    PASS: libgomp.c/../libgomp.c-c++-common/for-11.c (test for excess errors)
    [-PASS:-]{+FAIL:+} libgomp.c/../libgomp.c-c++-common/for-11.c execution test

    PASS: libgomp.c/../libgomp.c-c++-common/for-12.c (test for excess errors)
    [-PASS:-]{+FAIL:+} libgomp.c/../libgomp.c-c++-common/for-12.c execution test

    PASS: libgomp.c/../libgomp.c-c++-common/for-3.c (test for excess errors)
    [-PASS:-]{+FAIL:+} libgomp.c/../libgomp.c-c++-common/for-3.c execution test

    PASS: libgomp.c/../libgomp.c-c++-common/for-5.c (test for excess errors)
    [-PASS:-]{+FAIL:+} libgomp.c/../libgomp.c-c++-common/for-5.c execution test

    PASS: libgomp.c/../libgomp.c-c++-common/for-6.c (test for excess errors)
    [-PASS:-]{+FAIL:+} libgomp.c/../libgomp.c-c++-common/for-6.c execution test

    PASS: libgomp.c/../libgomp.c-c++-common/for-9.c (test for excess errors)
    [-PASS:-]{+FAIL:+} libgomp.c/../libgomp.c-c++-common/for-9.c execution test

Same for 'libgomp.c++'.

It remains to be analyzed how '#pragma GCC diagnostic [...]' directives
can cause code generation changes; for now I'm working around the
"unexpected" '-Werror=array-bounds' diagnostics differently:

> |> (So I'll consider some GCN-specific '-Wno-array-bounds' if we don't
> |> get to resolve this otherwise, soon.)

'-Wno-error=array-bounds', precisely.  I've now pushed "[gcn]
Work-around libgomp 'error: array subscript 0 is outside array bounds of
‘__lds struct gomp_thread * __lds[0]’ [-Werror=array-bounds]' some more
[PR101484]" to master branch in commit
8168338684fc2bed576bb09202c63b3e9e678d92, see attached.


Grüße
 Thomas


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