[PATCH] Break dependencies in large loops containing reductions (LoopVectorize)

[Olivier Sallenave]

I benchmarked this patch (without the multiply-add nonsense) on POWER8 and got the following speedups :

MultiSource/Benchmarks/McCat/08-main/main

  -59.4169% +/- 40.2649%

MultiSource/Benchmarks/Prolangs-C/fixoutput/fixoutput

  -83.6948% +/- 82.1021%

SingleSource/UnitTests/2003-05-02-DependentPHI

  -33.8917% +/- 31.3964%

SingleSource/UnitTests/2003-07-06-IntOverflow

  -43.784% +/- 38.5492%

And the following slowdowns:

MultiSource/Applications/kimwitu++/kc

  80.6835% +/- 69.7813%

MultiSource/Applications/viterbi/viterbi

  35.2072% +/- 24.8361%

MultiSource/Benchmarks/7zip/7zip-benchmark

  9.8082% +/- 6.31851%

MultiSource/Benchmarks/nbench/nbench,pass,

  8.43677% +/- 7.81566%

Will have to investigate whether the slowdowns are related to spills... However it seems that, if we were able to fine tune this, it would be profitable.


http://reviews.llvm.org/D7514

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