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From: "amonakov at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/100363] gcc generating wider load/store than warranted at -O3
Date: Sat, 01 May 2021 22:54:42 +0000 [thread overview]
Message-ID: <bug-100363-4-9LlWxyjMDC@http.gcc.gnu.org/bugzilla/> (raw)
In-Reply-To: <bug-100363-4@http.gcc.gnu.org/bugzilla/>
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100363
Alexander Monakov <amonakov at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |amonakov at gcc dot gnu.org
--- Comment #7 from Alexander Monakov <amonakov at gcc dot gnu.org> ---
The github issue has a more relevant code quote:
#ifdef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS <-- this is enabled for ARCv2
279: PUP(sout) = PUP(sfrom);
#else
PUP(sout) = UP_UNALIGNED(sfrom);
#endif
Most likely the issue is that sout/sfrom are misaligned at runtime, while the
vectorized code somewhere relies on them being sufficiently aligned for a
'short'.
It is unsafe to dereference a misaligned pointer. The pointed-to-type must have
reduced alignment:
typedef unsigned short u16_u __attribute__((aligned(1)));
u16_u *sout = ...
u16_u *sfrom = (void *)(from - OFF);
(without -ffreestanding, memcpy/memmove is a portable way to express a
misaligned access)
https://trust-in-soft.com/blog/2020/04/06/gcc-always-assumes-aligned-pointer-accesses/
next prev parent reply other threads:[~2021-05-01 22:54 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-30 20:09 [Bug c/100363] New: " vgupta at synopsys dot com
2021-04-30 21:43 ` [Bug middle-end/100363] " pinskia at gcc dot gnu.org
2021-04-30 21:44 ` pinskia at gcc dot gnu.org
2021-04-30 21:56 ` vgupta at synopsys dot com
2021-04-30 22:02 ` torvalds@linux-foundation.org
2021-04-30 22:19 ` [Bug tree-optimization/100363] " pinskia at gcc dot gnu.org
2021-04-30 22:20 ` pinskia at gcc dot gnu.org
2021-04-30 22:33 ` vgupta at synopsys dot com
2021-05-01 22:54 ` amonakov at gcc dot gnu.org [this message]
2021-05-01 23:09 ` torvalds@linux-foundation.org
2021-05-03 7:41 ` rguenth at gcc dot gnu.org
2021-05-03 16:03 ` torvalds@linux-foundation.org
2021-05-03 16:18 ` torvalds@linux-foundation.org
2021-05-03 17:25 ` vgupta at synopsys dot com
2021-05-03 17:28 ` vgupta at synopsys dot com
2021-05-03 17:47 ` torvalds@linux-foundation.org
2021-05-03 18:45 ` vgupta at synopsys dot com
2021-05-03 19:43 ` pinskia at gcc dot gnu.org
2021-05-04 6:24 ` rguenth at gcc dot gnu.org
2021-05-04 19:33 ` vgupta at synopsys dot com
2021-05-05 6:32 ` rguenther at suse dot de
2021-05-05 19:59 ` ndesaulniers at google dot com
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