Re: Question on BIGGEST_ALIGNMENT in GCC on NetBSD/m68k

[John Paul Adrian Glaubitz <glaubitz%physik.fu-berlin.de@localhost>]

Hi Jeff,

On Mon, 2025-05-26 at 14:16 -0400, Jeffrey Walton wrote:
> I don't know about the 64 byte alignment on NetBSD. Maybe it was
> copied/pasted/modified from amd64? amd64 has a BIGGEST_ALIGNMENT of 64
> due to AVX512. Prior to that, I believe amd64 had a BIGGEST_ALIGNMENT
> of 32 due to AVX. (These were due to the aligned loads, like
> _mm256_load_epi32 (32-byte requirement) or _mm512_load_epi32 (64-byte
> requirement)).
> 
> For PowerPC with Altivec, I believe BIGGEST_ALIGNMENT should be 16.
> 
> I don't know if __ALTIVEC__ plays a part in BIGGEST_ALIGNMENT. That
> is, should BIGGEST_ALIGNMENT be 4 (for int) or 8 (for doubles) unless
> __ALTIVEC__ is defined; and if __ALTIVEC__ is defined, then
> BIGGEST_ALIGNMENT should be 16.

The alignment is specified in bits here, not bytes. Hence a BIGGEST_ALIGNMENT
of 64 means 8 bytes, not 64 bytes.

Adrian

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