From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <gcc-bugs-return-400197-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org>
Received: (qmail 27100 invoked by alias); 5 Sep 2012 13:05:50 -0000
Received: (qmail 27085 invoked by uid 22791); 5 Sep 2012 13:05:49 -0000
X-SWARE-Spam-Status: No, hits=-3.5 required=5.0	tests=ALL_TRUSTED,AWL,BAYES_00,TW_OV
X-Spam-Check-By: sourceware.org
Received: from localhost (HELO gcc.gnu.org) (127.0.0.1)    by sourceware.org (qpsmtpd/0.43rc1) with ESMTP; Wed, 05 Sep 2012 13:05:36 +0000
From: "neleai at seznam dot cz" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c/54491] New: interval membership optimization
Date: Wed, 05 Sep 2012 13:05:00 -0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: new
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: gcc
X-Bugzilla-Component: c
X-Bugzilla-Keywords:
X-Bugzilla-Severity: normal
X-Bugzilla-Who: neleai at seznam dot cz
X-Bugzilla-Status: UNCONFIRMED
X-Bugzilla-Priority: P3
X-Bugzilla-Assigned-To: unassigned at gcc dot gnu.org
X-Bugzilla-Target-Milestone: ---
X-Bugzilla-Changed-Fields:
Message-ID: <bug-54491-4@http.gcc.gnu.org/bugzilla/>
X-Bugzilla-URL: http://gcc.gnu.org/bugzilla/
Auto-Submitted: auto-generated
Content-Type: text/plain; charset="UTF-8"
MIME-Version: 1.0
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
X-SW-Source: 2012-09/txt/msg00363.txt.bz2

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54491

             Bug #: 54491
           Summary: interval membership optimization
    Classification: Unclassified
           Product: gcc
           Version: 4.8.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: neleai@seznam.cz


A common optimization to test range membership b \in [c,d] is to use integer
overflow as in function range below. 

gcc does this optimization when both c and d are constants. However inlining
disables this optimization. 

Same optimization can be automatically applied for c arbitrary expression and 
d=c+positive_constant 


unsigned int range(unsigned int b,unsigned int c){
  if (b-c<=42) return c;
  return b;
}
unsigned int foo(unsigned int b,unsigned int c){
  if (c<=b && b <=42+c) return c;
  return b;
}
unsigned int bar(unsigned int b){
  return foo(b,42);
}
unsigned int baz(unsigned int b){
  if (42<=b && b<=84) return 42;
  return b;
}

 .file "a.c"
  .text
  .p2align 4,,15
  .globl  range
  .type range, @function
range:
.LFB0:
  .cfi_startproc
  movl  %edi, %eax
  subl  %esi, %eax
  cmpl  $42, %eax
  movl  %esi, %eax
  cmova %edi, %eax
  ret
  .cfi_endproc
.LFE0:
  .size range, .-range
  .p2align 4,,15
  .globl  foo
  .type foo, @function
foo:
.LFB1:
  .cfi_startproc
  cmpl  %edi, %esi
  movl  %edi, %eax
  ja  .L5
  leal  42(%rsi), %edx
  cmpl  %edx, %edi
  cmovbe  %esi, %eax
.L5:
  rep; ret
  .cfi_endproc
.LFE1:
  .size foo, .-foo
  .p2align 4,,15
  .globl  bar
  .type bar, @function
bar:
.LFB2:
  .cfi_startproc
  cmpl  $41, %edi
  movl  %edi, %eax
  jbe .L10
  cmpl  $85, %edi
  movl  $42, %edx
  cmovb %edx, %eax
.L10:
  rep; ret

  .cfi_endproc
.LFE2:
  .size bar, .-bar
  .p2align 4,,15
  .globl  baz
  .type baz, @function
baz:
.LFB3:
  .cfi_startproc
  leal  -42(%rdi), %edx
  movl  $42, %eax
  cmpl  $42, %edx
  cmova %edi, %eax
  ret
  .cfi_endproc
.LFE3:
  .size baz, .-baz
  .ident  "GCC: (Debian 20120820-1) 4.8.0 20120820 (experimental) [trunk
revision 190537]"
  .section  .note.GNU-stack,"",@progbits