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* [Bug target/25112]  New: [m68k] Inefficient equality comparison with small integers
@ 2005-11-27  2:11 kazu at gcc dot gnu dot org
  2005-11-28  5:02 ` [Bug target/25112] [m68k] Suboptimal equality comparisons " pinskia at gcc dot gnu dot org
  0 siblings, 1 reply; 2+ messages in thread
From: kazu at gcc dot gnu dot org @ 2005-11-27  2:11 UTC (permalink / raw)
  To: gcc-bugs

Consider:

int bar (void);

void
foo (void)
{
  int a = bar ();
  if (a == 1)
    bar ();
}

./cc1 -quiet -O2 -m5200 -fomit-frame-pointer generates

foo:
        move.l %a2,-(%sp)
        lea bar,%a2
        jbsr (%a2)
        moveq #1,%d1
        cmp.l %d0,%d1
        jbne .L4
        jbsr (%a2)
.L4:
        move.l (%sp)+,%a2
        rts

Note that

        moveq #1,%d1
        cmp.l %d0,%d1

can be replaced with

        subq.l #1,%d1

as long as the comparison is either == or !=, and %d1 dies at the comparison.

A similar optimization can be done for an equality comparison with
a negative numbers between -8 and -1, inclusive.


-- 
           Summary: [m68k] Inefficient equality comparison with small
                    integers
           Product: gcc
           Version: 4.2.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: enhancement
          Priority: P3
         Component: target
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: kazu at gcc dot gnu dot org
GCC target triplet: m68k-elf


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=25112


^ permalink raw reply	[flat|nested] 2+ messages in thread
* [Bug target/25112] [m68k] Suboptimal equality comparisons with small integers
  2005-11-27  2:11 [Bug target/25112] New: [m68k] Inefficient equality comparison with small integers kazu at gcc dot gnu dot org
@ 2005-11-28  5:02 ` pinskia at gcc dot gnu dot org
  0 siblings, 0 replies; 2+ messages in thread
From: pinskia at gcc dot gnu dot org @ 2005-11-28  5:02 UTC (permalink / raw)
  To: gcc-bugs



------- Comment #1 from pinskia at gcc dot gnu dot org  2005-11-28 05:02 -------
Confirmed.


-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|0                           |1
   Last reconfirmed|0000-00-00 00:00:00         |2005-11-28 05:02:38
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=25112


^ permalink raw reply	[flat|nested] 2+ messages in thread
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2005-11-27  2:11 [Bug target/25112] New: [m68k] Inefficient equality comparison with small integers kazu at gcc dot gnu dot org
2005-11-28  5:02 ` [Bug target/25112] [m68k] Suboptimal equality comparisons " pinskia at gcc dot gnu dot org

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