[PATCH] powerpc: Fix POWER7/PPC64 performance regression on LE

[Adhemerval Zanella]

On 14-01-2015 03:15, Richard Henderson wrote:
> On 01/13/2015 05:18 PM, Adhemerval Zanella wrote:
>> On 13-01-2015 18:11, Richard Henderson wrote:
>>> On 01/13/2015 11:43 AM, Adhemerval Zanella wrote:
>>>> +	std	rWORD8, rWORD8SAVE(r1)
>>>> +	cfi_offset(rWORD8, rWORD8SAVE)
>>>> +	std	rWORD7, rWORD7SAVE(r1)
>>>> +	cfi_offset(rWORD7, rWORD7SAVE)
>>>> +	std	rOFF8, rOFF8SAVE(r1)
>>>> +	cfi_offset(rWORD7, rOFF8SAVE)
>>>> +	std	rOFF16, rOFF16SAVE(r1)
>>>> +	cfi_offset(rWORD7, rOFF16SAVE)
>>>> +	std	rOFF24, rOFF24SAVE(r1)
>>>> +	cfi_offset(rWORD7, rOFF24SAVE)
>>>> +	std	rOFF32, rOFF32SAVE(r1)
>>>> +	cfi_offset(rWORD7, rOFF32SAVE)
>>> Given a sequence of stores like this, it's better to
>>> put all of the cfi_offset annotations after the last store.
>>>
>>> By interspersing them like this, you're just adding unnecessary
>>> DW_CFA_advance opcodes to the unwind info.
>>>
>>>
>>> r~
>>>
>> I was not aware of this, but I think the performance implications for such
>> organization is just to unwind and debuggers, right?
>>
> True, and that's why this is interesting as a size optimization,
> because it'll "almost never" be used.
>
>
> r~
>
I will add this modification on my backlog and change when 2.22 opens, thanks
for spotting it.