From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <gcc-bugs-return-431955-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org>
Received: (qmail 21571 invoked by alias); 16 Oct 2013 14:11:49 -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
Received: (qmail 21506 invoked by uid 48); 16 Oct 2013 14:11:44 -0000
From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/57742] memset(malloc(n),0,n) -> calloc(n,1)
Date: Wed, 16 Oct 2013 14:11:00 -0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: changed
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: gcc
X-Bugzilla-Component: tree-optimization
X-Bugzilla-Version: 4.9.0
X-Bugzilla-Keywords:
X-Bugzilla-Severity: enhancement
X-Bugzilla-Who: rguenth at gcc dot gnu.org
X-Bugzilla-Status: NEW
X-Bugzilla-Priority: P3
X-Bugzilla-Assigned-To: unassigned at gcc dot gnu.org
X-Bugzilla-Target-Milestone: ---
X-Bugzilla-Flags:
X-Bugzilla-Changed-Fields:
Message-ID: <bug-57742-4-8H4n2o8nxu@http.gcc.gnu.org/bugzilla/>
In-Reply-To: <bug-57742-4@http.gcc.gnu.org/bugzilla/>
References: <bug-57742-4@http.gcc.gnu.org/bugzilla/>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: 7bit
X-Bugzilla-URL: http://gcc.gnu.org/bugzilla/
Auto-Submitted: auto-generated
MIME-Version: 1.0
X-SW-Source: 2013-10/txt/msg01099.txt.bz2

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57742

--- Comment #12 from Richard Biener <rguenth at gcc dot gnu.org> ---
(In reply to Marc Glisse from comment #11)
> (In reply to Richard Biener from comment #9)
> > because of points-to analysis being not context sensitive.
> 
> Is "context sensitivity" the thing that is missing to perform the obvious
> optimization (i=3) on the following code without adding restrict to q? If
> so, I assume I don't need to file a PR about it... (there are too many PRs
> that mention alias analysis, I can't find anything)

Yes, the fact that the return value p cannot be equal to q inside the
function is not exposable.

> int i;
> int* g(int n,int*q){
>   int*p=__builtin_malloc(n);
>   p[2]=3;
>   *q=5;
>   i=p[2];
>   return p;
> }
> 
> (the "easy" cases are when we don't return p (no "global" var) or when p and
> q have incompatible types (but malloc+memset seems to lose any type I could
> try to force on the pointer))