There may be cases where the compiler doesn't optimise as well as older C/C++ compilers (e.g. in my SIMD work, C/C++ code compiled with GCC occasionally compreh

There may be cases where the compiler doesn't optimise as well as older C/C++ compilers (e.g. in my SIMD work, C/C++ code compiled with GCC occasionally comprehensively beats both the same code compiled with Clang and equivalent Rust with rustc (both built on LLVM) due to better optimisations and instruction selection: not a language issue), or where the pure-Rust libraries aren't as optimised as C/C++ equivalents. However, my experience is that it is rarely a lot slower.