[PATCH] D35888: Changed basic cost of Store operation on X86.

[Elena Demikhovsky via Phabricator via llvm-commits]

delena added a comment.

> Maybe I am wrong but the instruction cost is the cost relative to the cost of a typical instruction. TTI does not operates in terms of microarchitecture: u-ops etc. Why do we need a general function which is only for X86? How will other architectures need it? If everyone is happy with getOperationCost why X86 is not? Is it possible to have this functionality in X86TTI without changing general TTI?

The second option is to customize the getOperationCost() for X86.  Agree, it is also a way to provide target specific cost. Is that what you suggest?

> BTW ARM has LDM/STM (load and store multiple instructions) which can be quite heavy comparing to a typical instruction.

May be ARM should also customize load/store? I don't know. X86 hits performance regression due to wrong estimation of unroll factor against LSD.


Repository:
  rL LLVM

https://reviews.llvm.org/D35888