From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <gcc-bugs-return-332436-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org>
Received: (qmail 2342 invoked by alias); 29 Sep 2010 19:41:23 -0000
Received: (qmail 2328 invoked by uid 22791); 29 Sep 2010 19:41:22 -0000
X-SWARE-Spam-Status: No, hits=-2.3 required=5.0	tests=ALL_TRUSTED,AWL,BAYES_00,MISSING_MID,TW_DR
X-Spam-Check-By: sourceware.org
Received: from localhost (HELO gcc.gnu.org) (127.0.0.1)    by sourceware.org (qpsmtpd/0.43rc1) with ESMTP; Wed, 29 Sep 2010 19:41:18 +0000
From: "mikpe at it dot uu.se" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug rtl-optimization/45813] alias analysis problem ?
X-Bugzilla-Reason: CC
X-Bugzilla-Type: changed
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: gcc
X-Bugzilla-Component: rtl-optimization
X-Bugzilla-Keywords:
X-Bugzilla-Severity: normal
X-Bugzilla-Who: mikpe at it dot uu.se
X-Bugzilla-Status: UNCONFIRMED
X-Bugzilla-Priority: P3
X-Bugzilla-Assigned-To: unassigned at gcc dot gnu.org
X-Bugzilla-Target-Milestone: ---
X-Bugzilla-Changed-Fields:
In-Reply-To: <bug-45813-4@http.gcc.gnu.org/bugzilla/>
References: <bug-45813-4@http.gcc.gnu.org/bugzilla/>
X-Bugzilla-URL: http://gcc.gnu.org/bugzilla/
Auto-Submitted: auto-generated
Content-Type: text/plain; charset="UTF-8"
MIME-Version: 1.0
Date: Thu, 30 Sep 2010 01:18:00 -0000
Mailing-List: contact gcc-bugs-help@gcc.gnu.org; run by ezmlm
Precedence: bulk
List-Id: <gcc-bugs.gcc.gnu.org>
List-Archive: <http://gcc.gnu.org/ml/gcc-bugs/>
List-Post: <mailto:gcc-bugs@gcc.gnu.org>
List-Help: <mailto:gcc-bugs-help@gcc.gnu.org>
Sender: gcc-bugs-owner@gcc.gnu.org
X-SW-Source: 2010-09/txt/msg03160.txt.bz2
Message-ID: <20100930011800.0VlE1QUUuq08Puc59ba_X8wJ6eGMQBXGIS8aKNQAtZw@z>

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45813

--- Comment #9 from Mikael Pettersson <mikpe at it dot uu.se> 2010-09-29 19:41:08 UTC ---
I can reproduce it with crosses to arm-elf and arm-linux-gnueabi.  The
combination of -mthumb (1 not 2) and -fno-omit-frame-pointer is the trigger.
GCC 4.3.5 works, 4.4 and 4.5 generate broken code, 4.6 works.

gcc-4.3.5 -march=armv5te -mthumb -fno-omit-frame-pointer -Os generates:

ReadLE16U:
        push    {r7, lr}
        ldrb    r3, [r0]
        sub     sp, sp, #8
        add     r7, sp, #0
        add     r2, r7, #6
        strb    r3, [r2]
        ldrb    r3, [r0, #1]
        mov     sp, r7
        add     sp, sp, #8
        strb    r3, [r2, #1]
        ldrh    r0, [r2]
        @ sp needed for prologue
        pop     {r7, pc}

The second byte is correctly stored before the short is read and returned.

gcc-4.4-20100928 and gcc-4.5-20100923 generate:

ReadLE16U:
        push    {r7, lr}
        ldrb    r2, [r0]
        sub     sp, sp, #8
        add     r7, sp, #0
        add     r3, r7, #6
        mov     sp, r7
        strb    r2, [r3]
        add     sp, sp, #8
        ldrb    r2, [r0, #1]
        @ sp needed for prologue
        ldrh    r0, [r3]
        pop     {r7, pc}

The second byte is read but not written before the short is read.

gcc-4.6-20100925 generates:

ReadLE16U:
        push    {r0, r1, r7, lr}
        ldrb    r3, [r0]
        add     r7, sp, #0
        mov     sp, r7
        strb    r3, [r7, #6]
        ldrb    r3, [r0, #1]
        @ sp needed for prologue
        strb    r3, [r7, #7]
        ldrh    r0, [r7, #6]
        pop     {r1, r2, r7, pc}

This is correct.