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From: "ebotcazou at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug rtl-optimization/50065] -Os, -O2, -O3 optimization breaks LD/ST ordering on 32-bit SPARC
Date: Sat, 13 Aug 2011 10:12:00 -0000 [thread overview]
Message-ID: <bug-50065-4-VXFuQl4Ytv@http.gcc.gnu.org/bugzilla/> (raw)
In-Reply-To: <bug-50065-4@http.gcc.gnu.org/bugzilla/>
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50065
Eric Botcazou <ebotcazou at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |RESOLVED
CC| |ebotcazou at gcc dot
| |gnu.org
Resolution| |INVALID
--- Comment #2 from Eric Botcazou <ebotcazou at gcc dot gnu.org> 2011-08-13 10:10:47 UTC ---
> instruction 2C, clrb [%g1] corresponds to inline function 'spinlock_unlock'
> *(volatile unsigned char*)lock = 0;
>
> This happens before the lock protected content 'remap_barrier++', i.e.
>
> 30: c6 00 a0 00 ld [ %g2 ], %g3
> 34: 86 00 e0 01 inc %g3
> 38: 81 c3 e0 08 retl
> 3c: c6 20 a0 00 st %g3, [ %g2 ] ---> use the branch delay slot
>
> This is wrong and will cause serious lock issues under a multithreading
> environment.
On what grounds is this wrong exactly? The end of the code is equivalent to:
volatile unsigned char lock;
int remap_barrier;
remap_barrier++;
lock = 0;
It is perfectly valid for an optimizing C compiler to swap the two lines.
You want something like:
static inline void spin_unlock(char *lock)
{
__asm__ __volatile__("stb %%g0, [%0]" : : "r" (lock) : "memory");
}
next prev parent reply other threads:[~2011-08-13 10:11 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-08-12 21:49 [Bug c/50065] New: " tanzhangxi at gmail dot com
2011-08-13 4:33 ` [Bug rtl-optimization/50065] " pinskia at gcc dot gnu.org
2011-08-13 10:12 ` ebotcazou at gcc dot gnu.org [this message]
2011-08-14 1:30 ` tanzhangxi at gmail dot com
2011-08-14 4:42 ` tanzhangxi at gmail dot com
2011-08-14 9:38 ` mikpe at it dot uu.se
2011-08-14 13:00 ` ebotcazou at gcc dot gnu.org
2011-08-14 13:11 ` ebotcazou at gcc dot gnu.org
2011-08-14 22:43 ` tanzhangxi at gmail dot com
2011-08-15 8:52 ` ebotcazou at gcc dot gnu.org
2011-08-16 7:29 ` mikpe at it dot uu.se
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