[Bug middle-end/96625] Unnecessarily large assembly generated when a bit-offsetted higher-end end of a uint64_t-backed bitfield is shifted toward the high end (left) by its bit-offset

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96625

--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
There's no promotion on bitfields bigger than int, so yes, this would depend on
the frontends.  The zeroing of the upper bits is done by RTL expansion for
bit-field arithmetic.