[clang] Add __builtin_bswap128 (PR #198172)

[via cfe-commits]

Disservin wrote:

> Do we actually want to add this? There is `__builtin_bswapg` now, which is strictly better than the constant width builtins.

i leave that discussion to you :D 

seems like gcc and clang have kind of opposed opinions on this matter :D 

> Note, we don't have __builtin_bswapg and I don't think we should, one can
only byteswap something which has number of bits divisible by CHAR_BIT.

https://gcc.gnu.org/pipermail/gcc-patches/2026-May/716903.html

i was planing / about to open an issue for the `__builtin_bitreverse128` and came across this for bswap first

https://github.com/llvm/llvm-project/pull/198172