From: Brian Dessent <brian@dessent.net>
To: Bob Plantz <plantz@cds1.net>
Cc: Andrew Haley <aph@redhat.com>,
Robin-Vossen <robin-vossen@hotmail.com>,
gcc-help@gcc.gnu.org
Subject: Re: GNU C++ Inline Assembler
Date: Tue, 12 Aug 2008 02:29:00 -0000 [thread overview]
Message-ID: <48A0E23F.EE8BC28C@dessent.net> (raw)
In-Reply-To: <1218489833.5989.6.camel@bob-desktop>
Bob Plantz wrote:
> How can that be? The thing that matters is the machine code. Both
> syntaxes generate exactly the same machine code.
Because the MSVC style of inline assembler doesn't allow for specifying
any constraints such as which registers or stack slots are clobbered.
This means that compiler can't assume anything about the state before
and after the block, it must just throw away all dataflow information it
had before the block and assume everything was clobbered, leading to
tons of useless redundant loads/stores. The GNU style inline asm works
within the framework of the optimizing compiler, rather than outside it
by totally going behind it's back.
Read the long thread that starts here:
<http://gcc.gnu.org/ml/gcc/2004-05/threads.html#00070>.
Brian
next prev parent reply other threads:[~2008-08-12 1:08 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-08-10 21:39 Robin-Vossen
2008-08-11 6:37 ` Bob Plantz
2008-08-11 16:35 ` Robin-Vossen
2008-08-11 16:59 ` David Daney
2008-08-11 21:24 ` Andrew Haley
2008-08-12 1:08 ` Bob Plantz
2008-08-12 2:29 ` Brian Dessent [this message]
2008-08-12 8:56 ` Bob Plantz
2008-08-13 17:27 ` Robin-Vossen
2008-08-12 15:26 ` Ian Lance Taylor
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