[Bug rtl-optimization/45617] New: optimize bit shift+compare at RTL level

[Bug rtl-optimization/45617] New: optimize bit shift+compare at RTL level

[zsojka at seznam dot cz]

+++ This bug was initially created as a clone of Bug #20517 +++

>From comment #4:

----- testcase.c -----
_Bool foo(unsigned i)
{
        return (i >> 5) > 10;
}

_Bool bar(unsigned i)
{
        return i > (10 << 5) + 31;
}

int fooi(unsigned i)
{
        return (i >> 5) > 10;
}

int bari(unsigned i)
{
        return i > (10 << 5) + 31;
}
----------------------

Compiled with:
$ gcc-4.6.0-pre9999 tst6.c -O3 -S -m32 -fomit-frame-pointer
(svn r162190)

Results in:
foo:
        movl    4(%esp), %eax
        shrl    $5, %eax
        cmpl    $10, %eax
        seta    %al
        ret
bar:
        cmpl    $351, 4(%esp)
        seta    %al
        ret
fooi:
        movl    4(%esp), %eax
        shrl    $5, %eax
        cmpl    $10, %eax
        seta    %al
        movzbl  %al, %eax
        ret
bari:
        xorl    %eax, %eax
        cmpl    $351, 4(%esp)
        seta    %al
        ret


-- 
           Summary: optimize bit shift+compare at RTL level
           Product: gcc
           Version: 4.6.0
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P3
         Component: rtl-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: zsojka at seznam dot cz
GCC target triplet: x86(_64)-pc-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45617

[Bug rtl-optimization/45617] optimize bit shift+compare at RTL level

[zsojka at seznam dot cz]

------- Comment #1 from zsojka at seznam dot cz  2010-09-09 17:51 -------
Created an attachment (id=21756)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=21756&action=view)
Jakub's patch from PR20517 comment #6

gcc bootstrapped fine

The resulting code for foo() and fooi() is the same as for bar() and bari(),
respectively.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45617

[Bug rtl-optimization/45617] optimize bit shift+compare at RTL level

[jakub at gcc dot gnu dot org]

------- Comment #2 from jakub at gcc dot gnu dot org  2010-09-13 21:00 -------
Subject: Bug 45617

Author: jakub
Date: Mon Sep 13 21:00:03 2010
New Revision: 164257

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=164257
Log:
        PR rtl-optimization/45617
        * combine.c (simplify_comparison): Optimize (X >> N) {>,>=,<,<=} C
        even if low N bits of X aren't known to be zero.

        * gcc.target/i386/pr45617.c: New test.

Added:
    trunk/gcc/testsuite/gcc.target/i386/pr45617.c
Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/combine.c
    trunk/gcc/testsuite/ChangeLog


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45617

[Bug rtl-optimization/45617] optimize bit shift+compare at RTL level

[jakub at gcc dot gnu dot org]

------- Comment #3 from jakub at gcc dot gnu dot org  2010-09-13 21:10 -------
Committed.


-- 

jakub at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|                            |FIXED


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45617