From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <gcc-bugs-return-177756-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org>
Received: (qmail 22126 invoked by alias); 22 Feb 2006 12:47:48 -0000
Received: (qmail 22091 invoked by uid 48); 22 Feb 2006 12:47:43 -0000
Date: Wed, 22 Feb 2006 12:47:00 -0000
Message-ID: <20060222124743.22090.qmail@sourceware.org>
X-Bugzilla-Reason: CC
References: <bug-26406-6528@http.gcc.gnu.org/bugzilla/>
Subject: [Bug tree-optimization/26406] Fowardprop does harm for VRP to figure out if a point is non zero
In-Reply-To: <bug-26406-6528@http.gcc.gnu.org/bugzilla/>
Reply-To: gcc-bugzilla@gcc.gnu.org
To: gcc-bugs@gcc.gnu.org
From: "rguenth at gcc dot gnu dot org" <gcc-bugzilla@gcc.gnu.org>
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
X-SW-Source: 2006-02/txt/msg02502.txt.bz2
List-Id: <gcc-bugs.sourceware.org>



------- Comment #5 from rguenth at gcc dot gnu dot org  2006-02-22 12:47 -------
Of course we have the other case where we _have_ to propagate to optimize away
the test (gcc.dg/tree-ssa/20030807-2.c):

foo(int n)
{
  int *space = (int *)__builtin_alloca (n);

  if (space == 0)
    abort ();
  else
    bar (space);
}

where there is a 2nd use of space:

foo (n)
{
  int * space;
  void * D.1899;
  long unsigned int D.1898;

<bb 2>:
  D.1898_2 = (long unsigned int) n_1;
  D.1899_3 = __builtin_alloca (D.1898_2);
  space_4 = (int *) D.1899_3;
  if (space_4 == 0B) goto <L0>; else goto <L1>;

<L0>:;
  abort ();

<L1>:;
  bar (space_4);
  return;

}

So I think extending VRP is the only way to get both testcases optimized.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26406