Hal Finkel 139bfee84c [PowerPC] Enable late partial unrolling on the POWER7 ...

The P7 benefits from not have really-small loops so that we either have
multiple dispatch groups in the loop and/or the ability to form more-full
dispatch groups during scheduling. Setting the partial unrolling threshold to
44 seems good, empirically, for the P7. Compared to using no late partial
unrolling, this yields the following test-suite speedups:

SingleSource/Benchmarks/Adobe-C++/simple_types_constant_folding
	-66.3253% +/- 24.1975%
SingleSource/Benchmarks/Misc-C++/oopack_v1p8
	-44.0169% +/- 29.4881%
SingleSource/Benchmarks/Misc/pi
	-27.8351% +/- 12.2712%
SingleSource/Benchmarks/Stanford/Bubblesort
	-30.9898% +/- 22.4647%

I've speculatively added a similar setting for the P8. Also, I've noticed that
the unroller does not quite calculate the unrolling factor correctly for really
tiny loops because it neglects to account for the fact that not every loop body
replicant contains an ending branch and counter increment. I'll fix that later.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@225522 91177308-0d34-0410-b5e6-96231b3b80d8

2015-01-09 15:51:16 +00:00

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