[PATCH] Adding the loop vectorizer to the LTO pipeline

[Arnold Schwaighofer]

Hi all,

I would like to add the loop vectorizer to the LTO pipeline. During LTO more loops become countable (LICM moves the loop bound load out of the loop with the help of GlobalModRef) as a consequence we can vectorize more loops. Currently, we are not making use of this opportunity.

In my measurements on arm and x86 I saw no serious regressions and some bumps in performance. The one benchmark that benefits from this significantly is twolf/ref dataset (~5% on an arm architecture and ~5% on x86-64 sandy bridge) and some internal benchmarks.

Link time, as measured by timing the clang link step, increases by about 1% on average over the test-suite + externals.

The results on x86-64 -mavx -O3 -flto:


Performance Regressions - Execution Time		Δ	Previous Current σ	Δ (B)	σ (B)
MultiSource/Benchmarks/mafft/pairlocalalign		2.86%	22.2553	22.8911	0.0250	0.00%	0.0250


Performance Improvements - Execution Time			Δ	Previous Current σ	Δ (B)	σ (B)
SingleSource/Benchmarks/Misc/matmul_f64_4x4			-28.95%	0.2660	0.1890	0.0002	0.00%	0.0002
MultiSource/Benchmarks/TSVC/Symbolics-flt/Symbolics-flt		-16.08%	1.9063	1.5998	0.0020	0.00%	0.0020
MultiSource/Benchmarks/TSVC/ControlLoops-flt/ControlLoops-flt	-7.77%	2.5324	2.3356	0.0000	0.00%	0.0000
MultiSource/Benchmarks/TSVC/ControlLoops-dbl/ControlLoops-dbl	-6.07%	3.2678	3.0695	0.0005	0.00%	0.0005
MultiSource/Benchmarks/TSVC/Reductions-dbl/Reductions-dbl	-5.68%	3.5590	3.3570	0.0011	0.00%	0.0011
External/SPEC/CINT2000/300_twolf/300_twolf			-4.64%	3.5099	3.3471	0.0081	0.00%	0.0081
SingleSource/Benchmarks/Misc/mandel				-4.30%	0.4304	0.4119	0.0001	0.00%	0.0001
MultiSource/Benchmarks/TSVC/Reductions-flt/Reductions-flt	-2.93%	6.8906	6.6885	0.0007	0.00%	0.0007

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