[Clang] Consider adding `__builtin_rotate{left,right}g`

[philnik777]

I don't think there is much of a reason not to add them and would avoid a long list of if constexpr just for clang to go through the same code gen path in the end. A generic version would also add support for other integral types like _BitInt and __int128.

P.S. I don't really understand why this hasn't been done in the first place. Now we just have a bunch of g version for all the builtins as well as numbered ones without any benefit I can see.

[llvmbot]

@llvm/issue-subscribers-clang-frontend

Author: Nikolas Klauser (philnik777)

I don't think there is much of a reason not to add them and would avoid a long list of `if constexpr` just for clang to go through the same code gen path in the end. A generic version would also add support for other integral types like `_BitInt` and `__int128`.

P.S. I don't really understand why this hasn't been done in the first place. Now we just have a bunch of g version for all the builtins as well as numbered ones without any benefit I can see.

[pinskia]

GCC added __builtin_stdc_rotate_left/__builtin_stdc_rotate_right :
https://gcc.gnu.org/onlinedocs/gcc/Other-Builtins.html#index-_005f_005fbuiltin_005fstdc_005frotate_005fleft