ychen added a comment.

In D69327#1719109 <https://reviews.llvm.org/D69327#1719109>, @tejohnson wrote:

> I haven't read through the patch in detail yet, but from the description it 
> sounds like a cache is being added for the compile step outputs, e.g. the 
> bitcode output object of the "clang -flto=thin -c" step? Typically the build 
> system takes care of incremental build handling for these explicit outputs, 
> just as it would for a non-LTO clang compile output. Can you clarify the 
> motivation?


Hi Teresa, thanks for the feedback. I think the motivation is to provide an 
option that reliably caches thinLTO compile output regardless of the external 
setup of compiler cache or the platform is used. I'm not sure if compiler cache 
such as ccache could save `-fthin-link-bitcode` output and if there is a ccache 
equivalence on windows? Even if such tool exists, having linking phase caching 
managed by toolchain/linker and the compile phase by an external tool feels 
awkward and fragile. This patch mostly shares the implementation with linke 
phase caching.

Additionally, this also has a small benefit of trigging a little bit more 
caching because it is hashing IR instead of preprocessor output or even literal 
source file.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D69327/new/

https://reviews.llvm.org/D69327



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