[PATCH] ARM64: Combine shifts and uses to bit-extract instruction from different basic block

[yijiang]

Hi Quentin et al. ,

Could you help to review this patch? Thank you very much.

In this patch, I basically trying to do two things:
1) Try to detect potential opportunities, sink the shifts  and combine shifts and uses from different basic blocks that could generate bit-extract instruction and . 
2)  Recognize more patterns in instruction selection to generate bit-extract instructions, also try to make the instruction type more consistent to expose more opportunities in machine CSE. 

Now it is only enabled in ARM64. The test-suite result indicates that it will improve crafty by 1.21%, this can also be reproduced if the input is “ref” size. 
External/SPEC/CINT2000/186_crafty/186_crafty	-1.21%	9.5801	9.4639	-	-0.00%

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