Use temporary files in lto

[Sean Silva via llvm-commits]

On Fri, Apr 29, 2016 at 2:21 PM, Sean Silva <chisophugis at gmail.com> wrote:

>
>
> On Thu, Apr 28, 2016 at 4:23 PM, Rafael Espíndola <
> rafael.espindola at gmail.com> wrote:
>
>> This is the idea we chatted today to try to avoid mallocs os windows.
>> I was surprised to find this a small speedup up on linux
>
>
> The numbers you show below indicate a 0.07% difference in performance. It
> is somewhat spurious to call that "small". More like "negligible".
>
> To put some numbers on this, CPU's will clock differently depending on the
> number of cores available
>

this should say "cores in use"

-- Sean Silva


> . With only one core being used, they may be at their fastest clock, while
> if two cores are being used they will clock down by, say, 20% (and even
> more if more CPU's are being used).
>
> Assuming that LTO speed is linearly proportional to the clock frequency,
> then 0.07% performance difference corresponds to a difference of 0.4% in
> time spent at the highest clock frequency (in absolute terms, this is about
> 100ms out of a 30s LTO run). E.g. you may have touched the mouse during one
> run and not the other or you refreshed gmail in one run but not the other.
>
> -- Sean Silva
>
>
>> (with /tmp in
>> tmpfs), so I wonder if we are doing something funny in SmallVector.
>>
>> Linking llvm-as I got
>>
>> master: 29.774786873 seconds
>> patch 29.752283093 seconds
>>
>> Could one of you benchmark this on windows? If it is a performance win
>> there too I will clean the patch up and send for proper review.
>>
>> Cheers,
>> Rafael
>>
>
>
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