[Bug regression/16458] New: PowerPC - redundant compare

[Bug regression/16458] New: PowerPC - redundant compare

[gcc-bugzilla at gcc dot gnu dot org]

Description:
A non-optimal compare sequence is illustrated.  Two compares are being
done, one signed and the other unsigned.  One unsigned compare would
suffice.  Duplicate using gcc 3.5 and command line:

gcc -O3 -m64 -c test.c

Testcase:
unsigned int a, b;

int foo ()
{
  if (a == b) return 1;
  if (a > b)  return 2;
  if (a < b)  return 3;
  if (a != b) return 4;
  return 0;
}

Assembly:
      ld 9,.LC1@toc(2)
      li 3,1
      ld 11,.LC0@toc(2)
      lwz 10,0(9)
      lwz 0,0(11)
      cmpw 7,0,10   - signed compare of a and b
      cmplw 6,0,10  - unsigned compare of a and b
      beqlr- 7      - (a == b uses signed compare)
      li 3,2
      bgtlr- 6      - (a > b uses unsigned compare)
      li 3,4
      bgelr- 6      - (a != b uses unsigned compare)
      li 3,3
      blr



-- 
           Summary: PowerPC - redundant compare
           Product: gcc
           Version: 3.5.0
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P1
         Component: regression
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: steinmtz at us dot ibm dot com
                CC: gcc-bugs at gcc dot gnu dot org,steinmtz at us dot ibm
                    dot com
 GCC build triplet: powerpc64-linux
  GCC host triplet: powerpc64-linux
GCC target triplet: powerpc64-linux


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=16458

[Bug rtl-optimization/16458] PowerPC - redundant compare

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2004-07-09 18:42 -------
Confirmed, any PPC has this trouble, 32 bit or not.
This looks more like a middle-end problem or a target because when converting unsigned == 
unsigned from tree to RTL, it changes it to be a signed comparison.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
          Component|regression                  |rtl-optimization
     Ever Confirmed|                            |1
  GCC build triplet|powerpc64-linux             |
   GCC host triplet|powerpc64-linux             |
 GCC target triplet|powerpc64-linux             |powerpc*-*
           Keywords|                            |missed-optimization
   Last reconfirmed|0000-00-00 00:00:00         |2004-07-09 18:42:00
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=16458

[Bug middle-end/16458] PowerPC - redundant compare

[nathan at gcc dot gnu dot org]

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
         AssignedTo|unassigned at gcc dot gnu   |nathan at gcc dot gnu dot
                   |dot org                     |org
             Status|NEW                         |ASSIGNED


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=16458

[Bug middle-end/16458] PowerPC - redundant compare

[nathan at gcc dot gnu dot org]

------- Additional Comments From nathan at gcc dot gnu dot org  2004-11-11 08:39 -------
2004-11-11  Nathan Sidwell  <nathan@codesourcery.com>

	PR target/16458
	* config/rs6000/rs6000.c (rs6000_generate_compare): Generate an
	unsigned equality compare when we know the operands are unsigned.

this is a partial fix, the remainder is dependent on 18395, IMO

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
  BugsThisDependsOn|                            |18395
         AssignedTo|nathan at gcc dot gnu dot   |unassigned at gcc dot gnu
                   |org                         |dot org
             Status|ASSIGNED                    |NEW


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=16458

[Bug middle-end/16458] PowerPC - redundant compare

[cvs-commit at gcc dot gnu dot org]

------- Additional Comments From cvs-commit at gcc dot gnu dot org  2004-11-11 08:41 -------
Subject: Bug 16458

CVSROOT:	/cvs/gcc
Module name:	gcc
Changes by:	nathan@gcc.gnu.org	2004-11-11 08:40:43

Modified files:
	gcc            : ChangeLog 
	gcc/config/rs6000: rs6000.c 
	gcc/testsuite  : ChangeLog 
Added files:
	gcc/testsuite/gcc.dg: ppc-compare-1.c 

Log message:
	.:
	PR target/16458
	* config/rs6000/rs6000.c (rs6000_generate_compare): Generate an
	unsigned equality compare when we know the operands are unsigned.
	testsuite:
	PR target/16458
	* gcc.dg/ppc-compare-1.c: New.

Patches:
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/ChangeLog.diff?cvsroot=gcc&r1=2.6271&r2=2.6272
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/config/rs6000/rs6000.c.diff?cvsroot=gcc&r1=1.739&r2=1.740
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/testsuite/ChangeLog.diff?cvsroot=gcc&r1=1.4574&r2=1.4575
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/testsuite/gcc.dg/ppc-compare-1.c.diff?cvsroot=gcc&r1=NONE&r2=1.1



-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=16458