Enable ISL's small integer optimization
With small integer optimization (short: sio) enabled, ISL uses 32 bit
integers for its arithmetic and only falls back to a big integer library
(in the case of Polly: IMath) if an operation's result is too large.
This gives a massive performance boost for most application using ISL.
For instance, experiments with ppcg (polyhedral source-to-source
compiler) show speed-ups of 5.8 (compared to plain IMath), respectively
2.7 (compared to GMP).
In Polly, a smaller fraction of the total compile time is taken by ISL,
but the speed-ups are still very significant. The buildbots measure
compilation speed-up up to 1.8 (oourafft, floyd-warshall, symm). All
Polybench benchmarks compile in at least 9% less time, and about 20%
less on average.
Detailed Polybench compile time results (median of 10):
Reviewed By: grosser
Subscribers: Meinersbur, llvm-commits, pollydev
Differential Revision: http://reviews.llvm.org/D10506