[PATCH] powerpc: Fix logbl on power7 [BZ# 21280]

[Tulio Magno Quites Machado Filho]

Adhemerval Zanella <adhemerval.zanella@linaro.org> writes:

> On 21/03/2017 17:09, Tulio Magno Quites Machado Filho wrote:
>> Adhemerval Zanella <adhemerval.zanella@linaro.org> writes:
>> 
>>> On 20/03/2017 18:02, Tulio Magno Quites Machado Filho wrote:
>>>>  1. Fix the results for negative subnormals by ignoring the signal when
>>>>     normalizing the value.
>>>>  2. Fix the output when the high part is a power of 2 and the low part
>>>>     is a nonzero number with opposite sign.  This fix is based on commit
>>>>     380bd0fd2418f8988217de950f8b8ff18af0cb2b.
>>>
>>> It is not a blocker, but based on the complexity of the change and the 
>>> optimization real case usage, I wonder if it would be better to just remove 
>>> it and use the default implementation instead.
>> 
>> I tried to do that before fixing these, but the performance difference is
>> still around 2x.
>
> I would expect it, but the question is do we really care about the performance
> of logbl-ibm128 to maintain a separated implementation for power7+ only?

Yes, we still need it.
Considering your proposal was not a blocker, I plan to merge this fix.

Anyway, I agree in re-evaluating the removal of this optimization
in a few releases.

-- 
Tulio Magno