[PATCH] D76286: [X86][MC] Support enhanced relaxation for branch align

Mon Apr 6 22:20:45 PDT 2020

skan added a comment.

In D76286#1961436 <https://reviews.llvm.org/D76286#1961436>, @skan wrote:

> Applied D76286 <https://reviews.llvm.org/D76286>,D76475 <https://reviews.llvm.org/D76475> on commit 7b808b105f6aedc4066502b68b71cf205bafa582 <https://reviews.llvm.org/rG7b808b105f6aedc4066502b68b71cf205bafa582>
>
> I collected the memory usage for the prefix padding and NOP padding when building SPEC
>
> With LTO, the prefix padding solution consumes 17% more memory than NOP padding in geomean. The highest outlier is 43%.  Without LTO, the prefix padding solution consumes  5% more memory than NOP padding in geomean. The highest outlier is 28%.
>
> Options for NOP padding: 
>  -x86-align-branch-boundary=32  -x86-align-branch=fused+jcc+jmp+indirect+call+ret -x86-pad-max-prefix-size=0
>
> Options for prefix padding: 
>  -x86-align-branch-boundary=32  -x86-align-branch=fused+jcc+jmp+indirect+call+ret -x86-pad-max-prefix-size=5

Is the extra memory overhead acceptable to reviewers ? It occurs only when we need to align branches by prefix padding, and provide the user more choices for padding branches.

Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D76286/new/

https://reviews.llvm.org/D76286