[polly] r229820 - ScopDetection: Only detect scops that have at least one read and one write

[Tobias Grosser]

On 19.02.2015 06:31, Tobias Grosser wrote:
> Author: grosser
> Date: Wed Feb 18 23:31:07 2015
> New Revision: 229820
>
> URL: http://llvm.org/viewvc/llvm-project?rev=229820&view=rev
> Log:
> ScopDetection: Only detect scops that have at least one read and one write
>
> Scops that only read seem generally uninteresting and scops that only write are
> most likely initializations where there is also little to optimize.  To not
> waste compile time we bail early.
>
> Differential Revision: http://reviews.llvm.org/D7735

This change nicely reduces compile time with (-O3 -mllvm -polly) for 
several benchmarks (mostly polybench, but also several others). We see 
17 reductions between 67% and 20% and several more reductions below 20%.

http://llvm.org/perf/db_default/v4/nts/21604?num_comparison_runs=0&test_filter=&test_min_value_filter=&aggregation_fn=median&MW_confidence_lv=0.05&compare_to=21566&submit=Update

The performance of -O3 -mllvm -polly compared to -O3 is:

http//llvm.org/perf/db_default/v4/nts/21604?compare_to=21631

We still see several compile-time regressions (some caused by the import 
of the MIT licensed imath). However, there are still several low hanging 
fruits that should give good improvements.


Cheers,
Tobias