Evgeny Karpov <[email protected]> writes:
> In some cases, the alignment can be bigger than BIGGEST_ALIGNMENT.
>
> The issue was detected while building FFmpeg.
> It creates structures, most likely for AVX optimization.
>
> For instance:
> float __attribute__((aligned (32))) large_aligned_array[3];
>
> BIGGEST_ALIGNMENT could be up to 512 bits on x64.
> This patch has been added to cover this case without needing to
> change the FFmpeg code.
What goes wrong if we don't do this? I'm not sure from the description
whether it's a correctness fix, a performance fix, or whether it's about
avoiding wasted space.
> gcc/ChangeLog:
>
> * config/aarch64/aarch64-coff.h (ASM_OUTPUT_ALIGNED_LOCAL):
> Change alignment.
> ---
> gcc/config/aarch64/aarch64-coff.h | 10 ++++++++++
> 1 file changed, 10 insertions(+)
>
> diff --git a/gcc/config/aarch64/aarch64-coff.h
> b/gcc/config/aarch64/aarch64-coff.h
> index 17f346fe540..bf8e30b9c08 100644
> --- a/gcc/config/aarch64/aarch64-coff.h
> +++ b/gcc/config/aarch64/aarch64-coff.h
> @@ -58,6 +58,16 @@
> assemble_name ((FILE), (NAME)), \
> fprintf ((FILE), ",%lu\n", (ROUNDED)))
>
> +#define ASM_OUTPUT_ALIGNED_LOCAL(FILE, NAME, SIZE, ALIGNMENT) \
> + { \
> + unsigned HOST_WIDE_INT rounded = MAX ((SIZE), 1); \
> + unsigned HOST_WIDE_INT alignment = MAX ((ALIGNMENT), BIGGEST_ALIGNMENT);
> \
> + rounded += (alignment / BITS_PER_UNIT) - 1; \
> + rounded = (rounded / (alignment / BITS_PER_UNIT) \
> + * (alignment / BITS_PER_UNIT)); \
There's a ROUND_UP macro that could be used here.
Thanks,
Richard
> + ASM_OUTPUT_LOCAL (FILE, NAME, SIZE, rounded); \
> + }
> +
> #define ASM_OUTPUT_SKIP(STREAM, NBYTES) \
> fprintf (STREAM, "\t.space\t%d // skip\n", (int) (NBYTES))
