[PATCH] i586: Use a jump table in strcpy.S {BZ #22353]

[H.J. Lu]

On Mon, Oct 30, 2017 at 6:20 AM, Florian Weimer <fweimer@redhat.com> wrote:
> On 10/30/2017 02:12 PM, H.J. Lu wrote:
>
>>> What's the performance impact of the change?  Is it even worth to use a
>>> jump
>>> table here?
>>>
>>
>> I added 2 strcpy implementations to hjl/pr22353/master.  Jump table is
>> faster
>> than other non-SSE strcpy implementations because it can copy up to 4
>> bytes
>> at a time.
>
>
> To clarify, I meant replacing the jump table with conditional branches,
> basically getting rid of Duff's device.
>

I changed:

         BRANCH_TO_JMPTBL_ENTRY (L(SrcTable), %ecx, 4)

          .p2align 4
L(Src0):

to

        cmpb    $2, %cl
        je      L(Src2)
        ja      L(Src3)
        cmpb    $1, %cl
        je      L(Src1)

L(Src0):

Their performances are equivalent on Haswell.

Here is the updated patch I am going to check in.

Thanks.


-- 
H.J.
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