From: Denis Zaitsev <zzz@anda.ru>
To: Paul Brook <paul@codesourcery.com>
Cc: gcc@gcc.gnu.org, Michael Matz <matz@suse.de>, linux-gcc@vger.kernel.org
Subject: Re: [new-ra] GCC-3.3.2/x86: some suspicious behaviour
Date: Thu, 8 Jul 2004 23:18:56 +0600 [thread overview]
Message-ID: <20040708231856.B7162@natasha.ward.six> (raw)
In-Reply-To: <200407081752.57212.paul@codesourcery.com>; from paul@codesourcery.com on Thu, Jul 08, 2004 at 05:52:57PM +0100
On Thu, Jul 08, 2004 at 05:52:57PM +0100, Paul Brook wrote:
> On Thursday 08 July 2004 17:31, Denis Zaitsev wrote:
> > On Thu, Jul 08, 2004 at 04:46:33PM +0200, Michael Matz wrote:
> > > Hi,
> > >
> > > On Thu, 8 Jul 2004, Denis Zaitsev wrote:
> > > > So, what does these two commands mean:
> > > >
> > > >
> > > > movl %ecx, 16(%esp)
> > > > movl %esi, 20(%esp)
> > >
> > > It means that the compiler wasn't able to optimize them away. They do no
> > > harm. FWIW gcc 3.4 or the new-regalloc-branch don't have this problem.
> >
> > They don't harm. But to optimize _what_? So, what is the initial
> > meaning of these assignments? And why they appear only for the double
> > asm statement?
>
> They're storing the modified values of s and d back into their stack slots
> after the first asm. The compiler wasn't able to determine that these were
> dead stores.
>
> Remove the "extern inline" and compile with -O0. This will show you
> approximately what the code looks like before optimization.
Yes, this way the variables are really just stored back into their
stack locations. But in my case:
movl 20(%esp), %ecx
movl 16(%esp), %esi
movl %ecx, 16(%esp)
movl %esi, 20(%esp)
So, the stack slots seem to be swapped. Why?
prev parent reply other threads:[~2004-07-08 17:18 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2004-07-07 22:06 [new-ra] GCC-3.3.2/x86: some suspicious behaviour Denis Zaitsev
2004-07-08 14:46 ` Michael Matz
2004-07-08 16:31 ` Denis Zaitsev
2004-07-08 16:52 ` Paul Brook
2004-07-08 17:18 ` Denis Zaitsev [this message]
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