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Stuart Cook
cc0a60fd74
Always use the ThinLTO pipeline for pre-link optimizations When using cargo this was already effectively done for all dependencies as cargo passes -Clinker-plugin-lto without -Clto=fat/thin. -Clinker-plugin-lto assumes that ThinLTO will be used. The ThinLTO pre-link pipeline is faster than the fat LTO one. And according to the benchmarks in [^1] there is barely any runtime performance difference between executables that used fat LTO with the fat vs ThinLTO pre-link pipeline. This also helps avoid having yet another code path if we want to support Unified LTO (that is a single bitcode file that supports being used for both fat LTO and ThinLTO when using linker plugin LTO, we already support it when rustc does LTO as ThinLTO bitcode is enough of a superset of fat LTO bitcode that it happens to work by accident if you don't explicitly have a check preventing mixing of them for the current set of LTO features that rustc exposes.) I'm currently still investigating if rustc would benefit from Unified LTO and how exactly to integrate it. [^1]: https://discourse.llvm.org/t/rfc-a-unified-lto-bitcode-frontend/61774