On 25/03/2022 14:47, Jakub Jelinek via Gcc wrote:
On Fri, Mar 25, 2022 at 02:26:56PM +0000, Richard Earnshaw wrote:
Just to confirm that this is our final position. The 'int:0 field should be
ignored for the purposes of determining the parameter passing as it has no
effect on the layout of the type.
We do not feel that an update to the AAPCS or AAPCS64 is needed as the
wording already covers this.
Ok. So on the GCC side you need for both arm and aarch64 something similar
to the r12-6418-g3159da6c46568a7c change (of course on the ARM/AArch64 side
it will be in different spots etc.).
But generally, if you see during TYPE_FIELDS walk for argument/return value
passing decisions (both test whether something could be passed in registers
or say alignment decisions for those) rather than layout
DECL_BIT_FIELD (field) && integer_zerop (DECL_SIZE (field))
ignore it - if DECL_FIELD_CXX_ZERO_WIDTH_BIT_FIELD (field) then always,
otherwise arrange for 2 invocations in which one ignores them and one
doesn't and warns if the overall decisions change.
Jakub
Do we really need two passes? Surely, if we find a zero-width bitfield
in the type we just set a marker to note that it was found. If, at the
end of walking the type, it's still a candidate for passing in FP regs,
then we've identified an ABI change because previously we would not have
behaved this way.
R.
