[PATCH] D71261: [ThinLTO] upgrade IR symtab in parallel ahead of time

Tue May 19 22:30:21 PDT 2020

ychen marked 2 inline comments as done.
ychen added a comment.

In D71261#2045724 <https://reviews.llvm.org/D71261#2045724>, @MaskRay wrote:

> > Add an lld option(--cache-ir-symtab) to enable this behavior (default off). In the long run, I think it is beneficial to turn it on by default.
>
> I tested this patch internally. There is some minor performance loss turning on --cache-ir-symtab. That may be because we don't have mismatching versions of bitcode files.
>  I guess many users do the same (same version of bitcode files), so I am unsure this should be on by default.

This mostly benefits ThinLTO incremental build. When there are a lot of bitcode files need to be upgraded, the performance increase is obvious; if not, I expected the performance loss is very minor. There are some heuristics could help performance loss. For example, skip pre-upgrade when the number of candidate files is smaller than some threshold. Anyhow, I think it is reasonable to make it opt-in to begin with.

Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D71261/new/

https://reviews.llvm.org/D71261