[Bug middle-end/31271] Missing simple optimization

[Bug middle-end/31271] Missing simple optimization

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=31271

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |missed-optimization
      Known to work|4.7.1                       |

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
We produce in 4.7.0+

in_canforward(unsigned int):
.LFB0:
        .cfi_startproc
        andl    $224, %edi
        xorl    %eax, %eax
        cmpl    $224, %edi
        setne   %al
        ret


That is:
  D.2201_1 = in_2(D) & 224;
  D.2199_10 = D.2201_1 != 224;

I think we could do slightly better
((~in_2(D)) & 224) == 0

But only at exand time.
This gives:
        notl    %edi
        xorl    %eax, %eax
        testb   $-32, %dil
        setne   %al

Or for aarch64:
        mov     w8, #224
        bics    wzr, w8, w0
        cset    w0, ne
        ret

[Bug middle-end/31271] Missing simple optimization

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=31271

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |4.7.0

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
(In reply to Andrew Pinski from comment #2)
> 
> I think we could do slightly better
> ((~in_2(D)) & 224) == 0
> 
> But only at exand time.
> This gives:
>         notl    %edi
>         xorl    %eax, %eax
>         testb   $-32, %dil
>         setne   %al

x86_64 produces that in GCC 13 with r13-792-g29ae455901ac71 .

> 
> Or for aarch64:
>         mov     w8, #224
>         bics    wzr, w8, w0
>         cset    w0, ne
>         ret

For aarch64, it could define an instruction to catch:
(set (reg:CC_NZV 66 cc)
    (compare:CC_NZV (and:SI (not:SI (reg:SI 100))
            (const_int 224 [0xe0]))
        (const_int 0 [0])))


Anyways the original issue was fixed in GCC 4.7.0 and the small improvement for
x86_64 is in GCC 13. The aarch64 code generation is currently:
        and     w0, w0, 224
        cmp     w0, 224
        cset    w0, ne
        ret

Which is only slightly worse than what I proposed too.

[Bug middle-end/31271] Missing simple optimization

[rguenth at gcc dot gnu dot org]

------- Comment #1 from rguenth at gcc dot gnu dot org  2007-03-20 10:39 -------
Confirmed.  This is neither done at the tree nor at the rtl level.


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |rguenth at gcc dot gnu dot
                   |                            |org
             Status|UNCONFIRMED                 |NEW
          Component|rtl-optimization            |middle-end
     Ever Confirmed|0                           |1
   Last reconfirmed|0000-00-00 00:00:00         |2007-03-20 10:39:11
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31271