On Tue, Oct 27, 2020 at 11:49 PM Jan Hubicka <hubi...@ucw.cz> wrote:
>
> Hi,
> this patch avoid typeless storage in trailing_wide_ints. This improves
> TBAA disambiguation rate on cc1plus by 7%.
>
> Bootstrapped/regtested x86_64-linux, OK?
OK.
I guess if uint8_t would be a separate type from unsigned char that
would work as well but it is not.
Thanks,
Richard.
> * wide-int.h (trailing_wide_ints <N>): Turn len to array of structures
> so it does not imply typeless storage.
> (trailing_wide_ints <N>::operator): update
> (trailing_wide_ints <N>::operator []): Update.
> diff --git a/gcc/wide-int.h b/gcc/wide-int.h
> index 39cd5b9bd17..6eae46da12e 100644
> --- a/gcc/wide-int.h
> +++ b/gcc/wide-int.h
> @@ -1387,8 +1387,10 @@ private:
> /* The shared maximum length of each number. */
> unsigned char m_max_len;
>
> - /* The current length of each number. */
> - unsigned char m_len[N];
> + /* The current length of each number.
> + Avoid char array so the whole structure is not a typeless storage
> + that will, in turn, turn off TBAA on gimple, trees and RTL. */
> + struct {unsigned char len;} m_len[N];
>
> /* The variable-length part of the structure, which always contains
> at least one HWI. Element I starts at index I * M_MAX_LEN. */
> @@ -1470,7 +1472,7 @@ template <int N>
> inline trailing_wide_int
> trailing_wide_ints <N>::operator [] (unsigned int index)
> {
> - return trailing_wide_int_storage (m_precision, &m_len[index],
> + return trailing_wide_int_storage (m_precision, &m_len[index].len,
> &m_val[index * m_max_len]);
> }
>
> @@ -1479,7 +1481,7 @@ inline typename trailing_wide_ints <N>::const_reference
> trailing_wide_ints <N>::operator [] (unsigned int index) const
> {
> return wi::storage_ref (&m_val[index * m_max_len],
> - m_len[index], m_precision);
> + m_len[index].len, m_precision);
> }
>
> /* Return how many extra bytes need to be added to the end of the structure
