Re: [PATCH 09/17] m68k: Implement xor_unlock_is_negative_byte

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On 4/10/23 06:07, Matthew Wilcox wrote:
On Wed, Oct 04, 2023 at 12:14:10AM +1000, Greg Ungerer wrote:
On 3/10/23 06:07, Matthew Wilcox wrote:
00000918 <folio_unlock>:
       918:       206f 0004       moveal %sp@(4),%a0
       91c:       7001            moveq #1,%d0
       91e:       b190            eorl %d0,%a0@
       920:       2010            movel %a0@,%d0
       922:       4a00            tstb %d0
       924:       6a0a            bpls 930 <folio_unlock+0x18>
       926:       42a7            clrl %sp@-
       928:       2f08            movel %a0,%sp@-
       92a:       4eba fafa       jsr %pc@(426 <folio_wake_bit>)
       92e:       508f            addql #8,%sp
       930:       4e75            rts

fwiw, here's what folio_unlock looks like today without any of my
patches:

00000746 <folio_unlock>:
      746:       206f 0004       moveal %sp@(4),%a0
      74a:       43e8 0003       lea %a0@(3),%a1
      74e:       0891 0000       bclr #0,%a1@
      752:       2010            movel %a0@,%d0
      754:       4a00            tstb %d0
      756:       6a0a            bpls 762 <folio_unlock+0x1c>
      758:       42a7            clrl %sp@-
      75a:       2f08            movel %a0,%sp@-
      75c:       4eba fcc8       jsr %pc@(426 <folio_wake_bit>)
      760:       508f            addql #8,%sp
      762:       4e75            rts

Same number of instructions, but today's code has slightly longer insns,
so I'm tempted to take the win?

Yes, I reckon so.


We could use eori instead of eorl, at least according to table 3-9 on
page 3-8:

EOR Dy,<ea>x L Source ^ Destination → Destination ISA_A
EORI #<data>,Dx L Immediate Data ^ Destination → Destination ISA_A

Oh.  I misread.  It only does EORI to a data register; it can't do EORI
to an address.

400413e6 <folio_unlock>:
400413e6:       206f 0004       moveal %sp@(4),%a0
400413ea:       2010            movel %a0@,%d0
400413ec:       0a80 0000 0001  eoril #1,%d0
400413f2:       2080            movel %d0,%a0@
400413f4:       2010            movel %a0@,%d0
400413f6:       4a00            tstb %d0
400413f8:       6c0a            bges 40041404 <folio_unlock+0x1e>
400413fa:       42a7            clrl %sp@-
400413fc:       2f08            movel %a0,%sp@-
400413fe:       4eba ff30       jsr %pc@(40041330 <folio_wake_bit>)
40041402:       508f            addql #8,%sp
40041404:       4e75            rts

But that is still worse anyway.

Yup.  Looks like the version I posted actually does the best!  I'll
munge that into the patch series and repost.  Thanks for your help!

No worries. Sorry I didn't notice it earlier, but glad it is sorted now.

Regards
Greg





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