From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <gcc-bugs-return-156596-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org>
Received: (qmail 14195 invoked by alias); 2 Sep 2005 09:54:57 -0000
Mailing-List: contact gcc-bugs-help@gcc.gnu.org; run by ezmlm
Precedence: bulk
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 14175 invoked by uid 48); 2 Sep 2005 09:54:53 -0000
Date: Fri, 02 Sep 2005 09:54:00 -0000
Message-ID: <20050902095453.14174.qmail@sourceware.org>
From: "rguenth at gcc dot gnu dot org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
In-Reply-To: <20050720134633.22568.arndt@jjj.de>
References: <20050720134633.22568.arndt@jjj.de>
Reply-To: gcc-bugzilla@gcc.gnu.org
Subject: [Bug rtl-optimization/22568] Should use cmov in some stituations
X-Bugzilla-Reason: CC
X-SW-Source: 2005-09/txt/msg00190.txt.bz2
List-Id: <gcc-bugs.sourceware.org>


------- Additional Comments From rguenth at gcc dot gnu dot org  2005-09-02 09:54 -------
Blindly applying ifcvt to something like

int a,b;
void foo(int flag)
{
  int x;
  if (flag)
    x=a,a=b,b=x;
}

because we're presented with

  if (flag)
  {
    int reg_a = a;
    x = reg_a;
    int reg_b = b;
    a = reg_b;
    b = x;
  }

and we get cmovs for loading a,b into pseudos instead of
loading them unconditionally.  F.i.

int a,b;
void foobar(int flag)
{
  if (flag)
    a = b;
}

will become

foobar:
        movl    4(%esp), %eax   # flag, flag
        testl   %eax, %eax      # flag
        cmovne  b, %edx # b,, b
        movl    a, %eax # a, tmp61
        cmovne  %edx, %eax      # b,, tmp61
        movl    %eax, a # tmp61, a
        ret

notice how we special-cased the _store_ to use a temporary.  I'll
try applying the same for loads.

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=22568