On Mon, Aug 25, 2025 at 1:52 PM Thomas Munro <thomas.munro@gmail.com> wrote:
> > struct { PgAioHandleState v:8; } state;
>
> This preserves type safety and compiles to strb two properties we
> want, but it seems to waste space (look at the offsets for the
> stores):
>
> a.out[0x1000005f8] <+140>: ldr x8, [sp, #0x8]
> a.out[0x1000005fc] <+144>: strb wzr, [x8, #0x8]
> a.out[0x100000600] <+148>: ldr x8, [sp, #0x8]
> a.out[0x100000604] <+152>: strb wzr, [x8, #0x4]
Sorry, I didn't make that very clear: that's open source clang 17
compiling assignment of zero to two neighbouring wrapped bitfields
with your trick. Probably easier to look at the struct layout with
pahole or printf offsetof(...) or sizeof() to see that PgAioHandle
grows by 9 bytes of padding, something Andres obviously felt pretty
strongly about if he felt the need to summon bitfields...
