How to control LTO

[GregBowyer]

I am not sure quite what to do here.

I have a tool that is built in rust and uses clang (through clang-sys).

I am greeted to a very aggressive link, as it looks like my linker is doing LTO for all clang

[65 / 66] Compiling Rust bin rework_includes (1 files); 3204s linux-sandbox

I am not sure what the ideal solution is here, but maybe we need to pass through linkopts or have some way to constrain lto?

[mfarrugi]

AFAIU lto does not run by default for rust or cc, do you have a particular command line causing the problem? How confident are you this is caused by lto?

[mfarrugi]

I have since built some crates with rustc_flags = ["--codegen=lto", and it is indeed much slower, but it should be off by default.

[GregBowyer]

I am going to call this issue aged out

[UebelAndre]

Perhaps #566 would solve for something here?

[hlopko]

It is in my queue to document how (and maybe fix things so it's possible) to do ThinLTO across Rust and C++.

[GregBowyer]

I am pretty sure there is good LTO here, just this specific issue is old bazel, toolchains and environments as well as deep llvm magics that I think I would struggle to even reproduce today ;)