I've implemented a `simd_splat` intrinsic, a function that puts the same value in each SIMD lane. LLVM wasn't handling the previous workaround (a manual shuffle) very well. https://github.com/rust-lang/rust/pull/151346 the intrinsic is now used by stdarch and portable_simd: - https://github.com/rust-lang/stdarch/pull/2003 - https://github.com/rust-lang/portable-simd/pull/501 This intrinsic fixes a bunch of long-standing optimization issues, and appears to have sped up compile times for some crates too. #rustlang