From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <gcc-bugzilla@gcc.gnu.org>
Received: by sourceware.org (Postfix, from userid 48)
 id D98653851C00; Tue, 28 Apr 2020 23:56:36 +0000 (GMT)
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org D98653851C00
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gcc.gnu.org;
 s=default; t=1588118196;
 bh=wVir3YIRULFSrq50Cah+lttZr6s/L0Y4smyPBTcWwLg=;
 h=From:To:Subject:Date:From;
 b=un3h9tJktCA4FZdyocnzHQ0xXvGJMJXrgCST5RRavhdoHql9Orz4xVxEraOExpGez
 bn6XWKskmHgbUUyc1RPLoW+upeuA+mySWD+0HIxn6K/dT7xEo3QNcIjvdDv+KS0H2+
 0FobMDgt1XmJXYQ5cT+X39bzWiell7/dUis/IpN8=
From: "gabravier at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/94836] New: Failure to optimize condition
 based on known value of static variable
Date: Tue, 28 Apr 2020 23:56:36 +0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: new
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: gcc
X-Bugzilla-Component: tree-optimization
X-Bugzilla-Version: 10.0
X-Bugzilla-Keywords: 
X-Bugzilla-Severity: normal
X-Bugzilla-Who: gabravier at gmail dot com
X-Bugzilla-Status: UNCONFIRMED
X-Bugzilla-Resolution: 
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: bug_id short_desc product version bug_status
 bug_severity priority component assigned_to reporter target_milestone
Message-ID: <bug-94836-4@http.gcc.gnu.org/bugzilla/>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
X-Bugzilla-URL: http://gcc.gnu.org/bugzilla/
Auto-Submitted: auto-generated
MIME-Version: 1.0
X-BeenThere: gcc-bugs@gcc.gnu.org
X-Mailman-Version: 2.1.29
Precedence: list
List-Id: Gcc-bugs mailing list <gcc-bugs.gcc.gnu.org>
List-Unsubscribe: <http://gcc.gnu.org/mailman/options/gcc-bugs>,
 <mailto:gcc-bugs-request@gcc.gnu.org?subject=unsubscribe>
List-Archive: <https://gcc.gnu.org/pipermail/gcc-bugs/>
List-Post: <mailto:gcc-bugs@gcc.gnu.org>
List-Help: <mailto:gcc-bugs-request@gcc.gnu.org?subject=help>
List-Subscribe: <http://gcc.gnu.org/mailman/listinfo/gcc-bugs>,
 <mailto:gcc-bugs-request@gcc.gnu.org?subject=subscribe>
X-List-Received-Date: Tue, 28 Apr 2020 23:56:37 -0000

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D94836

            Bug ID: 94836
           Summary: Failure to optimize condition based on known value of
                    static variable
           Product: gcc
           Version: 10.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: gabravier at gmail dot com
  Target Milestone: ---

int f(int x)
{
    static int s;

    if (s)
        s =3D x;

    return s;
}

This can be optimized to `return 0`. This transformation is done by LLVM, b=
ut
not by GCC

LLVM -O3 outputs :

f(int): # @f(int)
  xor eax, eax
  ret

GCC -O3 outputs :

f(int):
  mov eax, DWORD PTR f(int)::s[rip]
  test eax, eax
  je .L1
  mov DWORD PTR f(int)::s[rip], edi
  mov eax, edi
.L1:
  ret

(see also https://godbolt.org/z/FzpjCb)=