[Patch] Tuning the strategy in SLP vectoriezer

[Yi Jiang]

Hi, 

In this patch we are trying to do two things:
1) If the width of vectorization list candidate is bigger than vector reg width, we will break it down to fit the vector reg.
2) We do not vectorize the width which is not power of two. 

Here is the performance result of the change and we use ref input. Any comments and suggestions are appreciated. 



Performance Regressions - Execution Time	Δ	Previous	Current	σ	Δ (B)	σ (B)
External/SPEC/CINT95/134_perl/134_perl	2.76%	2.9533	3.0348	0.0024	0.00%	0.0024


Performance Improvements - Execution Time	Δ	Previous	Current	σ	Δ (B)	σ (B)
External/SPEC/CFP2000/177_mesa/177_mesa	-6.97%	21.1910	19.7130	0.0223	0.00%	0.0223
SingleSource/Benchmarks/BenchmarkGame/partialsums	-5.19%	0.2969	0.2815	-	0.00%	-
External/SPEC/CFP2000/188_ammp/188_ammp	-1.54%	88.2623	86.9050	0.0823	0.00%	0.0823


 

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