> For example, the all-inference benchmarks improve by about 10%, an LLVM-heavy workload shows a similar ~10% gain, and building corecompiler.ji improves by 13–16% with BOLT. When combined with PGO and LTO, total improvements of up to ~23% have been observed.

> To build a BOLT-optimized Julia, run the following commands

Is BOLT the default build (eg. fetched by juliaup) on the supported Linux x86_64 and aarch64? I'm assuming not, based on the wording here, but I'm interested in what the blocker is and whether there's plans to make it part of the default build process. Is it considered as yet immature? Are there other downsides to it than the harmless warnings the post mentions?