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 446B1385B835; Thu, 16 Apr 2020 11:28:24 +0000 (GMT)
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 446B1385B835
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gcc.gnu.org;
 s=default; t=1587036504;
 bh=j4DPXmr00+lLdlg2klpZeEt3NCP23AwpA0KAWOmciyg=;
 h=From:To:Subject:Date:From;
 b=n1RJWvVyqRz6f6AQNWLKtEDOcsjHkyw97z432iQBBHqKhBY956UrcU06nC3Z4QsAJ
 qkwz/t47V+/eKCv+ifdPW3kF4UrCcnU1LX1/HVB3USl6PLuaNLHdzlYvXUe/ICcbi+
 ch3IMsXR4TNs/+q6NbOR3matmflI5B49E6TrHRZg=
From: "soap at gentoo dot org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/94617] New: Simple if condition not optimized
Date: Thu, 16 Apr 2020 11:28:24 +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: soap at gentoo dot org
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-94617-4@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: Thu, 16 Apr 2020 11:28:24 -0000

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D94617

            Bug ID: 94617
           Summary: Simple if condition not optimized
           Product: gcc
           Version: 10.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: soap at gentoo dot org
  Target Milestone: ---

Given the following C++ snippet

  const char* vanilla_bandpass(int a, int b, int x, const char* low, const
char* high)
  {
      const bool within_interval { (a <=3D x) && (x < b) };
      return (within_interval ? high : low);
  }

GCC trunk yields with -O3 -march=3Dznver2 the following assembly

  vanilla_bandpass(int, int, int, char const*, char const*):
          mov     rax, r8
          cmp     edi, edx
          jg      .L4
          cmp     edx, esi
          jge     .L4
          ret
  .L4:
          mov     rax, rcx
          ret

which is terrible. On the other hand, Clang emits

  vanilla_bandpass(int, int, int, char const*, char const*):
          cmp     edx, esi
          cmovge  r8, rcx
          cmp     edi, edx
          cmovg   r8, rcx
          mov     rax, r8
          ret

which is a lot better. There exists an unbranched version for which I'm not
100% certain whether it's free of UB:

  #include <cstdint>

  const char* funky_bandpass(int a, int b, int x, const char* low, const ch=
ar*
high)
  {
      const bool within_interval { (a <=3D x) && (x < b) };
      const auto low_ptr =3D reinterpret_cast<uintptr_t>(low) *
(!within_interval);
      const auto high_ptr =3D reinterpret_cast<uintptr_t>(high) *
within_interval;

      const auto ptr_sum =3D low_ptr + high_ptr;
      const auto* result =3D reinterpret_cast<const char*>(ptr_sum);
      return result;
  }

which yields

  funky_bandpass(int, int, int, char const*, char const*):
          cmp     edi, edx
          setle   al
          cmp     edx, esi
          setl    dl
          and     eax, edx
          mov     edx, eax
          xor     edx, 1
          movzx   edx, dl
          movzx   eax, al
          imul    rcx, rdx
          imul    rax, r8
          add     rax, rcx
          ret

which is jump-free and in practice executes at the same observable rate as
Clang's assembly, but still looks needlessly complex. Clang manages to comp=
ile
this code to the same assembly as vanilla_bandpass.

Any chance of getting the optimizer ironed out for this?=