Great article. I read the tail call article when it appeared and was also very confused by the results - no relation to Python but I tuned luau interpreter to bits a few years ago and there just wasn’t a 10% opportunity there based on very careful inspection of assembly; I filed this away as “maybe CPython interpreter loop is weird” but the reality is more interesting.
https://mendeddrum.org/@fanf/114135155417228009
P.S. I checked and this affects luau as well. If you use clang-19 or clang-20 in production, I recommend using `-mllvm -tail-dup-pred-size=256 -mllvm -tail-dup-succ-size=256` as a workaround in the meantime. I've let the Luau folks know, hopefully they keep track of the pending LLVM fix and/or adjust the CMake settings accordingly if this never gets fixed...