Both clang and GCC support multi-core LTO, as does Rust. However, you have to partition the code, so the more cores you use the less benefit to LTO. Rust partit

Both clang and GCC support multi-core LTO, as does Rust. However, you have to partition the code, so the more cores you use the less benefit to LTO. Rust partitions by crate by default, but it can increase parallelism by partitioning each crate. I think "fat LTO" is the term typically used for whole-program, or at least in the case of Rust, whole-crate LTO, whereas "thin LTO" is what you get when you LTO partitions and then link those together normally. For clang and GCC, you can either have them automatically partition the code for thin LTO , or do it explicitly via your Makefile rules[1]. [1] Interestingly, GCC actually invokes Make internally to implement thin LTO, which lets it play nice with GNU Make's job control and obey the -j switch.