public inbox for gcc-bugs@sourceware.org
help / color / mirror / Atom feed
* [Bug middle-end/23664] New: fold does not change (a&C1)+(b&C2) to (a&C1)|(b&C2) iff (C1 & C2) == 0
@ 2005-09-01  0:40 pinskia at gcc dot gnu dot org
  2005-09-01  0:42 ` [Bug middle-end/23664] " pinskia at gcc dot gnu dot org
  2005-09-17  2:12 ` pinskia at gcc dot gnu dot org
  0 siblings, 2 replies; 3+ messages in thread
From: pinskia at gcc dot gnu dot org @ 2005-09-01  0:40 UTC (permalink / raw)
  To: gcc-bugs

These two functions should produce the same asm:
int f(int a, int b)
{
  return (a&0xF)+(b&0xF0);
}
int f1(int a, int b)
{
  return (a&0xF)|(b&0xF0);
}
For PPC, we get:
_f:
        rlwinm r4,r4,0,24,27
        rlwinm r3,r3,0,28,31
        add r3,r3,r4
        blr
_f1:
        rlwinm r4,r4,0,24,27
        rlwimi r3,r4,0,0,27
        blr

Which shows the | is more efficient than the + one.

-- 
           Summary: fold does not change (a&C1)+(b&C2) to (a&C1)|(b&C2) iff
                    (C1 & C2) == 0
           Product: gcc
           Version: 4.1.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: enhancement
          Priority: P2
         Component: middle-end
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: pinskia at gcc dot gnu dot org
                CC: gcc-bugs at gcc dot gnu dot org
GCC target triplet: powerpc-*-*
OtherBugsDependingO 19987
             nThis:


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23664


^ permalink raw reply	[flat|nested] 3+ messages in thread
* [Bug middle-end/23664] fold does not change (a&C1)+(b&C2) to (a&C1)|(b&C2) iff (C1 & C2) == 0
  2005-09-01  0:40 [Bug middle-end/23664] New: fold does not change (a&C1)+(b&C2) to (a&C1)|(b&C2) iff (C1 & C2) == 0 pinskia at gcc dot gnu dot org
@ 2005-09-01  0:42 ` pinskia at gcc dot gnu dot org
  2005-09-17  2:12 ` pinskia at gcc dot gnu dot org
  1 sibling, 0 replies; 3+ messages in thread
From: pinskia at gcc dot gnu dot org @ 2005-09-01  0:42 UTC (permalink / raw)
  To: gcc-bugs


------- Additional Comments From pinskia at gcc dot gnu dot org  2005-09-01 00:42 -------
I should give credit to LLVM's instruction combine pass which have this.

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23664


^ permalink raw reply	[flat|nested] 3+ messages in thread
* [Bug middle-end/23664] fold does not change (a&C1)+(b&C2) to (a&C1)|(b&C2) iff (C1 & C2) == 0
  2005-09-01  0:40 [Bug middle-end/23664] New: fold does not change (a&C1)+(b&C2) to (a&C1)|(b&C2) iff (C1 & C2) == 0 pinskia at gcc dot gnu dot org
  2005-09-01  0:42 ` [Bug middle-end/23664] " pinskia at gcc dot gnu dot org
@ 2005-09-17  2:12 ` pinskia at gcc dot gnu dot org
  1 sibling, 0 replies; 3+ messages in thread
From: pinskia at gcc dot gnu dot org @ 2005-09-17  2:12 UTC (permalink / raw)
  To: gcc-bugs


------- Additional Comments From pinskia at gcc dot gnu dot org  2005-09-17 02:12 -------
Confirmed.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|                            |1
   Last reconfirmed|0000-00-00 00:00:00         |2005-09-17 02:12:40
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23664


^ permalink raw reply	[flat|nested] 3+ messages in thread
end of thread, other threads:[~2005-09-17  2:12 UTC | newest]

Thread overview: 3+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2005-09-01  0:40 [Bug middle-end/23664] New: fold does not change (a&C1)+(b&C2) to (a&C1)|(b&C2) iff (C1 & C2) == 0 pinskia at gcc dot gnu dot org
2005-09-01  0:42 ` [Bug middle-end/23664] " pinskia at gcc dot gnu dot org
2005-09-17  2:12 ` pinskia at gcc dot gnu dot org

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).