[Bug target/31557] New: return 0x80000000UL code gen can be improved

[Bug target/31557] New: return 0x80000000UL code gen can be improved

[pinskia at gcc dot gnu dot org]

Testcase:
unsigned int f(void)
{
  return 0x80000001UL;
}

This should be able to done in three instructions:
.f:
        li 3,1
        oris 3,3,0x8000
        blr

Right now it is done as:
.L.f:
        li 3,0
        ori 3,3,32768
        sldi 3,3,16
        ori 3,3,1
        blr
Which is (0x8000 << 16) | 1 but (0x8000 << 16) is what is done for oris.


-- 
           Summary: return 0x80000000UL code gen can be improved
           Product: gcc
           Version: 4.3.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: enhancement
          Priority: P3
         Component: target
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: pinskia at gcc dot gnu dot org
GCC target triplet: powerpc64-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31557

[Bug target/31557] return 0x80000000UL code gen can be improved

[pinskia at gcc dot gnu dot org]

------- Comment #1 from pinskia at gcc dot gnu dot org  2007-07-02 21:35 -------
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         |2007-07-02 21:35:45
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31557

[Bug target/31557] return 0x80000000UL code gen can be improved

[bje at gcc dot gnu dot org]

------- Comment #2 from bje at gcc dot gnu dot org  2009-05-14 05:19 -------
Still present in GCC 4.5.0 20090513.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31557

[Bug target/31557] return 0x80000000UL code gen can be improved

[PHHargrove at lbl dot gov]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31557

Paul H. Hargrove <PHHargrove at lbl dot gov> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |PHHargrove at lbl dot gov

--- Comment #3 from Paul H. Hargrove <PHHargrove at lbl dot gov> 2012-08-13 23:03:06 UTC ---
FWIW, 4.8.0 20120809 w/ -O1 or higher is now using just 4 instructions instead
of 5.  So, "half way there".


.L.f:
        lis 3,0x8000
        ori 3,3,1
        rldicl 3,3,0,32
        blr

[Bug target/31557] return 0x80000000UL code gen can be improved

[PHHargrove at lbl dot gov]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31557

--- Comment #4 from Paul H. Hargrove <PHHargrove at lbl dot gov> 2012-08-14 00:31:14 UTC ---
(In reply to comment #3)
> FWIW, 4.8.0 20120809 w/ -O1 or higher is now using just 4 instructions instead
> of 5.  So, "half way there".
> 
> 
> .L.f:
>         lis 3,0x8000
>         ori 3,3,1
>         rldicl 3,3,0,32
>         blr

That was for a 64-bit target, where the need to zero the upper half of r3
(which is 0xffffffff due to sign extension of 0x8000 by 'lis') accounts for the
4th instruction.  So, there is still room for improvement using the originally
proposed 3-instruction sequence (since 'oris' won't sign-extend as 'lis' does).


For a 32-bit target, it appears that GCC 4.8.0 20120809 has reached the desired
three instructions:

f:
        lis 3,0x8000
        ori 3,3,1
        blr

[Bug target/31557] return 0x80000000UL code gen can be improved

[bergner at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=31557

Peter Bergner <bergner at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |FIXED
                 CC|                            |bergner at gcc dot gnu.org
             Status|REOPENED                    |RESOLVED

--- Comment #7 from Peter Bergner <bergner at gcc dot gnu.org> ---
(In reply to Segher Boessenkool from comment #6)
> Actually, huh, *not* fixed on trunk yet.

This was fixed in GCC 13.  Marking it as FIXED.

[Bug target/31557] return 0x80000000UL code gen can be improved

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=31557

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |13.0