[PATCH] [AArch64] Improve and enable the SeparateConstOffsetFromGEP for AArch64 backend.

[Hao Liu]

> This is not quite what I had in mind... when I said that we should disable the transformation, I did not mean that you should disable the entire pass, but rather, that you should only disable the part of SeparateConstOffsetFromGEP that breaks apart GEPs into ptrtoint/inttoptr when useAA is true like CGP does. Does SeparateConstOffsetFromGEP not convey benefits without this part of the transformation? Can you try implementing the same thing by breaking the GEPs into simpler ones like CGP does when useAA is true?
Hi Hal,

I think I understand your point now. I've attached a new patch. It will do arithmetic transformation only when the useAA() returns false, or it will transform a complex GEP into several simpler GEPs like CGP does.
The correctness has been tested. The performance test has not finished yet. But the assembly code looks similar to the old patch for cortex-a57. If the result is better than the old patch, I'll remove the logic about transformation to ptrtoint/inttoptr.

Review please.

Thanks,
-Hao

http://reviews.llvm.org/D5864