From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <gcc-return-167598-listarch-gcc=gcc.gnu.org@gcc.gnu.org>
Received: (qmail 20953 invoked by alias); 18 Mar 2011 13:26:44 -0000
Received: (qmail 20942 invoked by uid 22791); 18 Mar 2011 13:26:42 -0000
X-SWARE-Spam-Status: No, hits=-1.6 required=5.0	tests=AWL,BAYES_00,DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,RCVD_IN_DNSWL_NONE
X-Spam-Check-By: sourceware.org
Received: from mo-p00-ob.rzone.de (HELO mo-p00-ob.rzone.de) (81.169.146.160)    by sourceware.org (qpsmtpd/0.43rc1) with ESMTP; Fri, 18 Mar 2011 13:26:37 +0000
X-RZG-AUTH: :LXoWVUeid/7A29J/hMvvT2k715jHQaJercGObUOFkj18odoYNahU4Q==
X-RZG-CLASS-ID: mo00
Received: from [192.168.0.22]	(business-188-111-022-002.static.arcor-ip.net [188.111.22.2])	by post.strato.de (fruni mo58) (RZmta 25.8)	with ESMTPA id p056abn2ICvjuN ; Fri, 18 Mar 2011 14:26:35 +0100 (MET)
Message-ID: <4D835D8A.5000400@gjlay.de>
Date: Fri, 18 Mar 2011 13:26:00 -0000
From: Georg-Johann Lay <avr@gjlay.de>
User-Agent: Thunderbird 2.0.0.24 (X11/20100302)
MIME-Version: 1.0
To: "Paulo J. Matos" <pocmatos@gmail.com>
CC: gcc@gcc.gnu.org
Subject: Re: avr compilation
References: <ilv67b$au6$1@dough.gmane.org>
In-Reply-To: <ilv67b$au6$1@dough.gmane.org>
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: 7bit
X-IsSubscribed: yes
Mailing-List: contact gcc-help@gcc.gnu.org; run by ezmlm
Precedence: bulk
List-Id: <gcc.gcc.gnu.org>
List-Archive: <http://gcc.gnu.org/ml/gcc/>
List-Post: <mailto:gcc@gcc.gnu.org>
List-Help: <http://gcc.gnu.org/ml/>
Sender: gcc-owner@gcc.gnu.org
X-SW-Source: 2011-03/txt/msg00256.txt.bz2

Paulo J. Matos schrieb:
> Hi all,
> 
> I am looking at the avr backend in order to try to sort some things out
> on my own backend.
> 
> One of the tests I am doing is by compiling the following:
> int x = 0x1010;
> int y = 0x0101;
> 
> int add(void)
> {
>   return x+y;
> }
> 
> It compiles to (in gcc-4.3.5_avr with -Os)
> add:
> /* prologue: function */
> /* frame size = 0 */
>         lds r18,y
>         lds r19,(y)+1
>         lds r24,x
>         lds r25,(x)+1
>         add r18,r24
>         adc r19,r25
>         mov r24,r18
>         mov r25,r19
> /* epilogue start */
>         ret
> 
> I don't know much avr assembler so bear with me but I would expect this

note that the last moves are two QI moves, the add is HI.

Without splitting HI the moves will disappear, try -fno-split-wide-types.

Johann

> to be written:
> add:
> /* prologue: function */
> /* frame size = 0 */
>         lds r18,y
>         lds r19,(y)+1
>         lds r24,x
>         lds r25,(x)+1
>         add r24,r18
>         adc r25,r19
> /* epilogue start */
>         ret
> 
> By inverting the add arguments we save two mov instructions.
> 
> If it can be written like this any ideas on why GCC is avoiding it?

Try newer version of gcc, like 4.5.2
> 
> Cheers,
> 
> -- 
> PMatos