From: Ian Lance Taylor <ian@wasabisystems.com>
To: Jamie Lokier <jamie@shareable.org>
Cc: gcc@gcc.gnu.org
Subject: Re: A question about "memory" clobbers in asm
Date: Fri, 17 Sep 2004 15:39:00 -0000 [thread overview]
Message-ID: <m3hdpx6jc2.fsf@gossamer.airs.com> (raw)
In-Reply-To: <20040917144519.GB31970@mail.shareable.org>
Jamie Lokier <jamie@shareable.org> writes:
Should this be on gcc-help?
> I'm having trouble understand when it's appropriate to use a "memory"
> clobber, when to use volatile, and when to use both. The manual is
> unclear to me. Although I see that someone has tried to clarify it
> since I last read it, it's still not obvious how "memory" is different
> from `volatile'.
Volatile means that the assembler instruction can not be deleted, even
if it appears to be useless.
Marking the instruction as clobbering memory means that if the
instruction is executed, then memory is clobbered in some undescribed
way. However, that clobbering is not important to proper execution of
the program, and the instruction can be deleted if the specified
side-effects turn out to be unnecessary.
At least, that is my understanding.
Ian
next prev parent reply other threads:[~2004-09-17 14:50 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2004-09-17 15:32 Jamie Lokier
2004-09-17 15:39 ` Ian Lance Taylor [this message]
2004-09-17 15:50 ` Jamie Lokier
2004-09-17 16:07 ` Nathan Sidwell
2004-09-17 18:02 ` Jamie Lokier
2004-09-18 1:52 ` Giovanni Bajo
2004-09-18 17:10 ` Jamie Lokier
2004-09-18 20:48 ` Giovanni Bajo
2004-09-20 7:37 ` tm_gccmail
2004-09-20 13:57 ` Paul Koning
2004-09-20 15:16 ` Dave Korn
2004-09-20 15:39 ` Nathan Sidwell
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