[polly] scop detection: detect regions bottom up

[Sebastian Pop]

Hi Star,

Star Tan wrote:
> >Here is a patch that makes scop detection to work bottom up.  On my huge C++
> >benchmark, the attached patch gets the overall sequential time spent in Polly
> >from 2151 seconds to 1573 seconds.
> Cool, the compile time is reduced by about 1/4. Could you tell me which benchmark do you use? Was it in LLVM test-suite?

Unfortunately I wouldn't be able to share my benchmark or parts of it, as I
suspect it has proprietary information.  However I have seen similar slow downs
in scop detection when compiling C++ code with polly and adding -g.  You can try
to add -ftime-report to your LLVM nightly test-suite runs and see how much time
is spent in scop detection.

> I have set up a LNT-based Polly performance tester using LLVM test-suite. Maybe I can help to evaluate your patch on these benchmarks tonight :)

It would be interesting to see the impact of my changes on other benchmarks.  Do
we have a build bot reporting compile time on the nightly test-suite?

> >I think we can add the newly created blocks to the region info.
> >
> >Another solution, and probably more difficult, is to avoid invalidating the
> >region info by trying to not split the blocks ending a region.  I'm not sure
> >about the impact of such a change on the codegen region versioning.
> Can I do anything to help you? Maybe I can help to fix this problem by avoiding invalidating the region info.

If you can come up with a patch solving the region info invalidation, that would
be awesome!

Thanks,
Sebastian
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