[llvm-commits] [LLVM, loop-unswitch, bugfix for #11429] Wrong behaviour for switches.

[Stepan Dyatkovskiy]

Hi. A made some fixes that improves compile-time:

1. Size heuristics changed. Now we calculate number of unswitching 
branches only once per loop.
2. Some checks was moved from UnswitchIfProfitable to 
processCurrentLoop, since it is not changed during processCurrentLoop 
iteration. It allows decide to skip some loops at an early stage.

I checked the compile-time on test

MultiSource/Benchmarks/Prolangs-C++/shapes/shapes
(there was compile time regression after my previous patch).

Relative to previous patch the compile-time improved on ~8.5%. Relative 
to old revisions (before r146578) the compile time is improved on ~2%.

Please find the patch in attachment for review.

-Stepan.

Stepan Dyatkovskiy wrote:
> Commited as r146578.
>
> Thanks.
> -Stepan.
>
> Dan Gohman wrote:
>> Thanks. The patch looks ok to me.
>>
>> Dan
>>
>> On Dec 10, 2011, at 6:22 AM, Stepan Dyatkovskiy wrote:
>>
>>> I fixed code heuristics. How it works now:
>>>
>>> 1. Calculate average number of produced instructions and basics blocks:
>>> number-of-instructions=curret-loop->number-of-instructions * unswitched-number
>>> number-of-bb=curret-loop->number-of-bb * unswitched-number
>>>
>>> 2. If number-of-instructions>   Threshold || number-of-bb*5>   Threshold, stop unswitching.
>>>
>>> By default Threshold is 50. But user can set custom threshold using -loop-unswitch-threshold<custom-threshold>   option. This option existed before my patch, and I kept it without changes though.
>>>
>>> I compiled ffmpeg (ffmpeg.org) with llvm + clang toolchain (with and without my patch). I got the next results:
>>>
>>> Without patch:   ffmpeg size is 7369612 bytes.
>>> Threshold = 50:  ffmpeg size is 7349132 bytes (less then in ToT version).
>>> Threshold = 200: ffmpeg size is 7439244 bytes.
>>>
>>> I also checked the ffmpeg build time in all cases it was 2 mins, 35 secs.
>>> Transcoding time with ffmpeg (mp3 ->   mp2) in all cases was also the same: process took 1 min, 19 secs.
>>>
>>> I added unit test that checks unswitch kicking in case of insufficient size. Unit tests and fixed patch (default threshold is 50) are attached to this post.
>>>
>>> Thanks.
>>> -Stepan.
>>
>
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