> Am 17.09.2018 um 19:11 schrieb Segher Boessenkool
> <seg...@kernel.crashing.org>:
>
> On Mon, Sep 17, 2018 at 10:50:58AM +0200, Ilya Leoshkevich wrote:
>>> Am 14.09.2018 um 23:35 schrieb Segher Boessenkool
>>> <seg...@kernel.crashing.org>:
>>> Could you please show generated code before and after this patch?
>>> I mean generated assembler code. What -S gives you.
>>
>> Before:
>>
>> foo4:
>> .LFB0:
>> .cfi_startproc
>> lt %r1,0(%r2)
>> jne .L2
>> lhi %r3,1
>> cs %r1,%r3,0(%r2)
>> .L2:
>> jne .L5
>> br %r14
>> .L5:
>> jg bar
>>
>> After:
>>
>> foo4:
>> .LFB0:
>> .cfi_startproc
>> lt %r1,0(%r2)
>> jne .L4
>> lhi %r3,1
>> cs %r1,%r3,0(%r2)
>> jne .L4
>> br %r14
>> .L4:
>> jg bar
>
> Ah. And a compiler of some weeks old gives
>
> foo4:
> .LFB0:
> .cfi_startproc
> lhi %r3,0
> lhi %r4,1
> cs %r3,%r4,0(%r2)
> jne .L4
> br %r14
> .L4:
> jg bar
>
> so this is all caused by the recent optimisation that avoids the "cs" if
> it can.
Could you please try building with -march=z13? I don’t see the „lt“
instruction in your output. On z196+ we try to speed up the code by
jumping around the „cs“ when possible.
