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From: "tanzhangxi at gmail dot com" <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: Sun, 14 Aug 2011 22:43:00 -0000 [thread overview]
Message-ID: <bug-50065-4-hkEgORCCX5@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
--- Comment #8 from Zhangxi Tan <tanzhangxi at gmail dot com> 2011-08-14 21:00:40 UTC ---
Thanks for the clear explanation.
I agree that a memory barrier would solve this issue.
Regarding the spinlock_unlock in linux, the regular arch_spin_unlock is
implemented with a single inline assembly. That will prevent the memory
reordering in C. However, for the 32-bit port the arch_write_unlock is still
defined as the following without a memory barrier in
arch/sparc/include/asm/spinlock_32.h
#define arch_write_unlock(rw) do { (rw)->lock = 0; } while(0)
OTH, the 64-bit implemention is ok. Or did I miss something here.
Anyway, I think this is a separated issue from this thread.
(In reply to comment #6)
> > The code is equivalent to
> >
> > volatile unsigned char lock;
> > int remap_barrier;
> >
> > while (atomic_test_and_set(lock)) {
> > while (lock) {
> > ;
> > }
> > }
> > remap_barrier++;
> > lock = 0;
> >
> > Eric: could you let me know you you think the code inside function
> > spinlock_lock(&remap_lock) is a NOP?
>
> I don't, you simply misquoted, I wrote "the end of the code". The first part
> of the spinlock implementation is correct, in particular you have the required
> memory barrier in spinlock_is_locked. The second part is not correct, as you
> don't have the memory barrier in spinlock_unlock.
>
> > Also, the arch_write_lock/unlock in the SPARC port of Linux uses a very
> > similar implementation.
>
> No, it precisely doesn't, it has the memory barrier in spinlock_unlock.
next prev parent reply other threads:[~2011-08-14 21:01 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
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 [this message]
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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