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

[Hao Liu]

>>! In D5864#54, @jingyue wrote:
> LGTM with some minor fixes. You may want to double check with ARM folks on performance. I remember Gerolf said he couldn't get the same performance numbers as you did. 
> 
> Thanks again for all the hard work! 

Hi Jingyue,

Thanks very much for your hard work on review, which really help me a lot.
I've committed the code in http://llvm.org/viewvc/llvm-project?view=revision&revision=222328 and http://llvm.org/viewvc/llvm-project?view=revision&revision=222331.

BTW, for the performance test, I also tested other revision by some slightly modifications such as:
(1) Always lower GEPs if there is more than one index despite wheter we found a constant.
(2) Call SeparateConstOffsetFromGEP pass before calling TargetPassConfig::addIRPasses() in AArch64TargetMachine.cpp.

The performance results are different. Some benchmarks are better, some benchmarks are worse. So I just think maybe we need further tuning in the future for better performance. Anyway, that's the future work.

Thanks,
-Hao

http://reviews.llvm.org/D5864