From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <gcc-help-return-50147-listarch-gcc-help=gcc.gnu.org@gcc.gnu.org>
Received: (qmail 6051 invoked by alias); 1 Jun 2012 09:44:07 -0000
Received: (qmail 6029 invoked by uid 22791); 1 Jun 2012 09:44:05 -0000
X-SWARE-Spam-Status: No, hits=-2.0 required=5.0	tests=AWL,BAYES_00,DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,FREEMAIL_ENVFROM_END_DIGIT,FREEMAIL_FROM,KHOP_RCVD_TRUST,KHOP_THREADED,RCVD_IN_DNSWL_LOW,RCVD_IN_HOSTKARMA_YE,TW_NX
X-Spam-Check-By: sourceware.org
Received: from mail-lpp01m010-f47.google.com (HELO mail-lpp01m010-f47.google.com) (209.85.215.47)    by sourceware.org (qpsmtpd/0.43rc1) with ESMTP; Fri, 01 Jun 2012 09:43:52 +0000
Received: by lags15 with SMTP id s15so1489637lag.20        for <gcc-help@gcc.gnu.org>; Fri, 01 Jun 2012 02:43:50 -0700 (PDT)
MIME-Version: 1.0
Received: by 10.112.38.161 with SMTP id h1mr1529819lbk.85.1338543830724; Fri, 01 Jun 2012 02:43:50 -0700 (PDT)
Received: by 10.152.13.37 with HTTP; Fri, 1 Jun 2012 02:43:50 -0700 (PDT)
In-Reply-To: <4FC876E2.5050706@gmail.com>
References: <CABOpGfvcfbsb1BZvaHqZjQZaq1EV8QOo9pyMuvdq-PeRs9-LGw@mail.gmail.com>	<mcrtxyv7dsf.fsf@dhcp-172-18-216-180.mtv.corp.google.com>	<CABOpGftg8j0jV5_rMyCD4+0smHFuydeddPrKNZ_y+ZShcyqaWw@mail.gmail.com>	<4FC876E2.5050706@gmail.com>
Date: Fri, 01 Jun 2012 09:44:00 -0000
Message-ID: <CABOpGfvj8Rj0=NhV9fgryTcrwcjbzA6jsA7-dsziVGnKpqD+dQ@mail.gmail.com>
Subject: Re: some questions about GCC's options
From: ohav chochmah <philomath868@gmail.com>
To: xunxun <xunxun1982@gmail.com>
Cc: Ian Lance Taylor <iant@google.com>, gcc-help <gcc-help@gcc.gnu.org>
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: quoted-printable
Mailing-List: contact gcc-help-help@gcc.gnu.org; run by ezmlm
Precedence: bulk
List-Id: <gcc-help.gcc.gnu.org>
List-Archive: <http://gcc.gnu.org/ml/gcc-help/>
List-Post: <mailto:gcc-help@gcc.gnu.org>
List-Help: <mailto:gcc-help-help@gcc.gnu.org>
Sender: gcc-help-owner@gcc.gnu.org
X-SW-Source: 2012-06/txt/msg00003.txt.bz2

On 6/1/12, xunxun <xunxun1982@gmail.com> wrote:
> =E4=BA=8E 2012/6/1 15:59, ohav chochmah =E5=86=99=E9=81=93:
>> On 6/1/12, Ian Lance Taylor<iant@google.com>  wrote:
>>> ohav chochmah<philomath868@gmail.com>  writes:
>>>
>>>> first, is momit-leaf-frame-pointer bad for debugging (in the way
>>>> fomit-frame-pointer can be)?
>>> It's not as bad.  It may still trip up some debuggers.
>>>
>> but not GDB?
>>
>>>> if not, why is it disabled by default
>>>> even when optimizing (as -Q --help=3Dtarget | grep omit reveals)?
>>> When optimizing on x86 or x86_64, -fomit-frame-pointer is the default
>>> anyhow.  -fomit-frame-pointer essentially implies
>>> -momit-leaf-frame-pointer.
>>>
>> I was sure that's the answer, but then is GCC lying to me?
>> ~ $ gcc -S tst.c -O2 -march=3Dnative -Q --help=3Doptimizers | grep omit
>>    -fomit-frame-pointer        		[disabled]
> x86 or x86_64?
>
> I remembered -fomit-frame-pointer enabled only on x86_64 by default.

x86_64.
according to the manual, "Starting with GCC version 4.6, the default
setting (when not optimizing for size) for 32-bit Linux x86 and 32-bit
Darwin x86 targets has been changed to =E2=80=98-fomit-frame-pointer=E2=80=
=99.   The
default can be reverted to =E2=80=98-fno-omit-frame-pointer=E2=80=99 by con=
figuring
GCC with the =E2=80=98--enable-frame-pointer=E2=80=99 configure option."  i=
t does not
mention x86_64.
the bottom-line seems to be, that -Q --help=3D<class> is sometimes inaccura=
te.


> Best Regards,
> xunxun

all the best.