Hi!
On 2021-07-19T10:46:35+0200, I wrote:
> | On 7/16/21 11:42 AM, Thomas Schwinge wrote:
> |> <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. [...]
> [...] 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]" [...]
> Now: "Awaiting a different solution, of course." ;-)
Well, I just stumbled over that one; please have a look at the attached
"GCN: Implement 'TARGET_ADDR_SPACE_ZERO_ADDRESS_VALID' [PR101484]".
I'm not very familiar with the GCN named address spaces -- in addition to
'__lds', which ones to include in 'TARGET_ADDR_SPACE_ZERO_ADDRESS_VALID',
and/or instead of 'as == ADDR_SPACE_LDS', which 'AS_[...]_P' conditional
to use?
'gcc/config/gcn/gcn.h':
/* Address spaces. */
enum gcn_address_spaces
{
ADDR_SPACE_DEFAULT = 0,
ADDR_SPACE_FLAT,
ADDR_SPACE_SCALAR_FLAT,
ADDR_SPACE_FLAT_SCRATCH,
ADDR_SPACE_LDS,
ADDR_SPACE_GDS,
ADDR_SPACE_SCRATCH,
ADDR_SPACE_GLOBAL
};
#define REGISTER_TARGET_PRAGMAS() do { \
c_register_addr_space ("__flat", ADDR_SPACE_FLAT); \
c_register_addr_space ("__flat_scratch", ADDR_SPACE_FLAT_SCRATCH); \
c_register_addr_space ("__scalar_flat", ADDR_SPACE_SCALAR_FLAT); \
c_register_addr_space ("__lds", ADDR_SPACE_LDS); \
c_register_addr_space ("__gds", ADDR_SPACE_GDS); \
c_register_addr_space ("__global", ADDR_SPACE_GLOBAL); \
} while (0);
#define STACK_ADDR_SPACE ADDR_SPACE_GLOBAL
#define DEFAULT_ADDR_SPACE \
((cfun && cfun->machine && !cfun->machine->use_flat_addressing) \
? ADDR_SPACE_GLOBAL : ADDR_SPACE_FLAT)
#define AS_SCALAR_FLAT_P(AS) ((AS) == ADDR_SPACE_SCALAR_FLAT)
#define AS_FLAT_SCRATCH_P(AS) ((AS) == ADDR_SPACE_FLAT_SCRATCH)
#define AS_FLAT_P(AS) ((AS) == ADDR_SPACE_FLAT \
|| ((AS) == ADDR_SPACE_DEFAULT \
&& DEFAULT_ADDR_SPACE == ADDR_SPACE_FLAT))
#define AS_LDS_P(AS) ((AS) == ADDR_SPACE_LDS)
#define AS_GDS_P(AS) ((AS) == ADDR_SPACE_GDS)
#define AS_SCRATCH_P(AS) ((AS) == ADDR_SPACE_SCRATCH)
#define AS_GLOBAL_P(AS) ((AS) == ADDR_SPACE_GLOBAL \
|| ((AS) == ADDR_SPACE_DEFAULT \
&& DEFAULT_ADDR_SPACE == ADDR_SPACE_GLOBAL))
#define AS_ANY_FLAT_P(AS) (AS_FLAT_SCRATCH_P (AS) || AS_FLAT_P (AS))
#define AS_ANY_DS_P(AS) (AS_LDS_P (AS) || AS_GDS_P (AS))
Additionally:
On 2021-07-19T12:10:59+0100, Andrew Stubbs <[email protected]> wrote:
> On 19/07/2021 09:46, Thomas Schwinge wrote:
>>> GCN already uses address 4 for this value because address 0 caused
>>> problems with null-pointer checks.
>>
>> Ugh. How much wasted bytes per what is that? (I haven't looked yet;
>> hopefully not per GPU thread?) Because:
>
> It's 4 bytes per gang. And that pointer is the only 8 bytes in the whole
> of LDS (OpenMP mostly uses stack and heap), so it's not so bad, but still.
>
> I did investigate the target macro that lets you control null pointer
> behaviour, but it didn't just work, and it wasn't important enough for
> me to spend more time on it so I let it go.
Maybe what we get per the above ('TARGET_ADDR_SPACE_ZERO_ADDRESS_VALID')
is already sufficient to also get rid of having to use "address 4 for
this value because address 0 caused problems with null-pointer checks"?
(I've not yet tried.)
Grüße
Thomas
>From 50fa0cc04cef6b5c471e380d42cd3d4e3ec4a965 Mon Sep 17 00:00:00 2001
From: Thomas Schwinge <[email protected]>
Date: Thu, 11 Jun 2026 21:41:10 +0200
Subject: [PATCH] GCN: Implement 'TARGET_ADDR_SPACE_ZERO_ADDRESS_VALID'
[PR101484]
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit
This is the proper fix to replace
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]",
commit 8168338684fc2bed576bb09202c63b3e9e678d92
"[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]".
PR target/101484
gcc/
* config/gcn/gcn.cc (TARGET_ADDR_SPACE_ZERO_ADDRESS_VALID): Implement.
libgomp/
* configure.tgt [GCN] (XCFLAGS): Don't add '-Wno-error=array-bounds'.
---
gcc/config/gcn/gcn.cc | 10 ++++++++++
libgomp/configure.tgt | 3 ---
2 files changed, 10 insertions(+), 3 deletions(-)
diff --git a/gcc/config/gcn/gcn.cc b/gcc/config/gcn/gcn.cc
index 18995d61e7b..ed27acfb8a1 100644
--- a/gcc/config/gcn/gcn.cc
+++ b/gcc/config/gcn/gcn.cc
@@ -1874,6 +1874,14 @@ gcn_addr_space_subset_p (addr_space_t subset, addr_space_t superset)
return false;
}
+static bool
+gcn_addr_space_zero_address_valid (addr_space_t as)
+{
+ if (as == ADDR_SPACE_LDS)
+ return true;
+ return false;
+}
+
static addr_space_t
gcn_addr_space_resolve_default (addr_space_t as)
{
@@ -8085,6 +8093,8 @@ gcn_dwarf_register_span (rtx rtl)
#define TARGET_ADDR_SPACE_POINTER_MODE gcn_addr_space_pointer_mode
#undef TARGET_ADDR_SPACE_SUBSET_P
#define TARGET_ADDR_SPACE_SUBSET_P gcn_addr_space_subset_p
+#undef TARGET_ADDR_SPACE_ZERO_ADDRESS_VALID
+#define TARGET_ADDR_SPACE_ZERO_ADDRESS_VALID gcn_addr_space_zero_address_valid
#undef TARGET_ADDR_SPACE_CONVERT
#define TARGET_ADDR_SPACE_CONVERT gcn_addr_space_convert
#undef TARGET_ARG_PARTIAL_BYTES
diff --git a/libgomp/configure.tgt b/libgomp/configure.tgt
index 46af75f978f..a74e966fdfd 100644
--- a/libgomp/configure.tgt
+++ b/libgomp/configure.tgt
@@ -181,9 +181,6 @@ case "${target}" in
amdgcn*-*-*)
config_path="gcn accel"
-
- #TODO PR101484
- XCFLAGS="$XCFLAGS -Wno-error=array-bounds"
;;
*)
--
2.34.1
