Re: [gcn] Work-around libgomp 'error: array subscript 0 is outside array bounds of ‘__lds struct gomp_thread * __lds[0]’ [-Werror=array-bounds]'

[Thomas Schwinge <thomas@codesourcery.com>]

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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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From 8168338684fc2bed576bb09202c63b3e9e678d92 Mon Sep 17 00:00:00 2001
From: Thomas Schwinge <thomas@codesourcery.com>
Date: Mon, 19 Jul 2021 23:11:38 +0200
Subject: [PATCH] =?UTF-8?q?[gcn]=20Work-around=20libgomp=20'error:=20array?=
 =?UTF-8?q?=20subscript=200=20is=20outside=20array=20bounds=20of=20?=
 =?UTF-8?q?=E2=80=98=5F=5Flds=20struct=20gomp=5Fthread=20*=20=5F=5Flds[0]?=
 =?UTF-8?q?=E2=80=99=20[-Werror=3Darray-bounds]'=20some=20more=20[PR101484?=
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With yesterday's commit 9f2bc5077debef2b046b6c10d38591ac324ad8b5 "[gcn]
Work-around libgomp 'error: array subscript 0 is outside array bounds of
‘__lds struct gomp_thread * __lds[0]’ [-Werror=array-bounds]' [PR101484]",
I did defuse the "unexpected" '-Werror=array-bounds' diagnostics that we see
as of commit a110855667782dac7b674d3e328b253b3b3c919b "Correct handling of
variable offset minus constant in -Warray-bounds [PR100137]".  However, these
'#pragma GCC diagnostic [...]' directives cause some code generation changes
(that seems unexpected, problematic!), which 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.

Overall, still awaiting a different solution, of course.

	libgomp/
	PR target/101484
	* configure.tgt [amdgcn*-*-*] (XCFLAGS): Add
	'-Wno-error=array-bounds'.
	* config/gcn/team.c: Remove '-Werror=array-bounds' work-around.
	* libgomp.h [__AMDGCN__]: Likewise.
---
 libgomp/config/gcn/team.c |  3 ---
 libgomp/configure.tgt     |  3 +++
 libgomp/libgomp.h         | 12 ------------
 3 files changed, 3 insertions(+), 15 deletions(-)

diff --git a/libgomp/config/gcn/team.c b/libgomp/config/gcn/team.c
index 94ce2f2dfeb..627210ea407 100644
--- a/libgomp/config/gcn/team.c
+++ b/libgomp/config/gcn/team.c
@@ -65,12 +65,9 @@ gomp_gcn_enter_kernel (void)
       void * __lds *arena_start = (void * __lds *)TEAM_ARENA_START;
       void * __lds *arena_free = (void * __lds *)TEAM_ARENA_FREE;
       void * __lds *arena_end = (void * __lds *)TEAM_ARENA_END;
-# pragma GCC diagnostic push
-# pragma GCC diagnostic ignored "-Warray-bounds" /*TODO PR101484 */
       *arena_start = team_arena;
       *arena_free = team_arena;
       *arena_end = team_arena + TEAM_ARENA_SIZE;
-# pragma GCC diagnostic pop
 
       /* Allocate and initialize the team-local-storage data.  */
       struct gomp_thread *thrs = team_malloc_cleared (sizeof (*thrs)
diff --git a/libgomp/configure.tgt b/libgomp/configure.tgt
index fe2bf1dac51..d4f1e741b5a 100644
--- a/libgomp/configure.tgt
+++ b/libgomp/configure.tgt
@@ -173,6 +173,9 @@ case "${target}" in
 
   amdgcn*-*-*)
 	config_path="gcn accel"
+
+	#TODO PR101484
+	XCFLAGS="$XCFLAGS -Wno-error=array-bounds"
 	;;
 
   *)
diff --git a/libgomp/libgomp.h b/libgomp/libgomp.h
index 4159cbe3334..8d25dc8e2a8 100644
--- a/libgomp/libgomp.h
+++ b/libgomp/libgomp.h
@@ -128,10 +128,7 @@ team_malloc (size_t size)
        : "=v"(result) : "v"(TEAM_ARENA_FREE), "v"(size), "e"(1L) : "memory");
 
   /* Handle OOM.  */
-# pragma GCC diagnostic push
-# pragma GCC diagnostic ignored "-Warray-bounds" /*TODO PR101484 */
   if (result + size > *(void * __lds *)TEAM_ARENA_END)
-# pragma GCC diagnostic pop
     {
       /* While this is experimental, let's make sure we know when OOM
 	 happens.  */
@@ -162,11 +159,8 @@ team_free (void *ptr)
      However, if we fell back to using heap then we should free it.
      It would be better if this function could be a no-op, but at least
      LDS loads are cheap.  */
-# pragma GCC diagnostic push
-# pragma GCC diagnostic ignored "-Warray-bounds" /*TODO PR101484 */
   if (ptr < *(void * __lds *)TEAM_ARENA_START
       || ptr >= *(void * __lds *)TEAM_ARENA_END)
-# pragma GCC diagnostic pop
     free (ptr);
 }
 #else
@@ -795,19 +789,13 @@ static inline struct gomp_thread *gcn_thrs (void)
 {
   /* The value is at the bottom of LDS.  */
   struct gomp_thread * __lds *thrs = (struct gomp_thread * __lds *)4;
-# pragma GCC diagnostic push
-# pragma GCC diagnostic ignored "-Warray-bounds" /*TODO PR101484 */
   return *thrs;
-# pragma GCC diagnostic pop
 }
 static inline void set_gcn_thrs (struct gomp_thread *val)
 {
   /* The value is at the bottom of LDS.  */
   struct gomp_thread * __lds *thrs = (struct gomp_thread * __lds *)4;
-# pragma GCC diagnostic push
-# pragma GCC diagnostic ignored "-Warray-bounds" /*TODO PR101484 */
   *thrs = val;
-# pragma GCC diagnostic pop
 }
 static inline struct gomp_thread *gomp_thread (void)
 {
-- 
2.30.2