LLVM 23 cuts stage2-O3 compile time by 6.75 percent, and precompiled headers cut MSVC and Clang builds of LLVM by about 45 percent

Sources: compile-time measurements
Summary: The post, dated 2026-08-21, measures LLVM 23 compile time and reports a 6.75 percent reduction. The post states that all its performance numbers refer to the stage2-O3 configuration on the LLVM compile-time tracker unless noted otherwise. It separately reports that building LLVM and Clang with precompiled headers cuts build time by about 45 percent, and that the precompiled-header build is on by default for MSVC and Clang and disabled for GCC, where extra template instantiations negate the benefit.
Why it matters: Every project built with an LLVM-based toolchain inherits the compile-time change, and the precompiled-header default changes what building LLVM itself costs in CI on MSVC and Clang.