3ad234f53b
bootstrap: Link LLVM as a dylib with ThinLTO (take 2) When building a distributed compiler on Linux where we use ThinLTO to create the LLVM shared object this commit switches the compiler to dynamically linking that LLVM artifact instead of statically linking to LLVM. The primary goal here is to reduce CI compile times, avoiding two+ ThinLTO builds of all of LLVM. By linking dynamically to LLVM we'll reuse the one ThinLTO step done by LLVM's build itself. Lots of discussion about this change can be found [here] and down. A perf run will show whether this is worth it or not! [here]: https://github.com/rust-lang/rust/pull/53245#issuecomment-417015334 --- This PR previously landed in https://github.com/rust-lang/rust/pull/56944, caused https://github.com/rust-lang/rust/issues/57111, and was reverted in https://github.com/rust-lang/rust/pull/57116. I've added one more commit here which should fix the breakage that we saw.
The driver crate is effectively the "main" function for the rust
compiler. It orchestrates the compilation process and "knits together"
the code from the other crates within rustc. This crate itself does
not contain any of the "main logic" of the compiler (though it does
have some code related to pretty printing or other minor compiler
options).
For more information about how the driver works, see the rustc guide.