Re: [PATCH v4 13/57] meson: Detect atomic128 support with optimization

[Peter Maydell]

On Wed, 3 May 2023 at 08:29, Richard Henderson
<richard.henderson@linaro.org> wrote:
>
> There is an edge condition prior to gcc13 for which optimization
> is required to generate 16-byte atomic sequences.  Detect this.
>
> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
> ---
>  accel/tcg/ldst_atomicity.c.inc | 38 ++++++++++++++++++-------
>  meson.build                    | 52 ++++++++++++++++++++++------------
>  2 files changed, 61 insertions(+), 29 deletions(-)
>



> @@ -676,28 +695,24 @@ static inline void store_atomic8(void *pv, uint64_t val)
>   *
>   * Atomically store 16 aligned bytes to @pv.
>   */
> -static inline void store_atomic16(void *pv, Int128 val)
> +static inline void ATTRIBUTE_ATOMIC128_OPT
> +store_atomic16(void *pv, Int128Alias val)
>  {
>  #if defined(CONFIG_ATOMIC128)
>      __uint128_t *pu = __builtin_assume_aligned(pv, 16);
> -    Int128Alias new;
> -
> -    new.s = val;
> -    qatomic_set__nocheck(pu, new.u);
> +    qatomic_set__nocheck(pu, val.u);
>  #elif defined(CONFIG_CMPXCHG128)
>      __uint128_t *pu = __builtin_assume_aligned(pv, 16);
>      __uint128_t o;
> -    Int128Alias n;
>
>      /*
>       * Without CONFIG_ATOMIC128, __atomic_compare_exchange_n will always
>       * defer to libatomic, so we must use __sync_val_compare_and_swap_16
>       * and accept the sequential consistency that comes with it.
>       */
> -    n.s = val;
>      do {
>          o = *pu;
> -    } while (!__sync_bool_compare_and_swap_16(pu, o, n.u));
> +    } while (!__sync_bool_compare_and_swap_16(pu, o, val.u));
>  #else
>      qemu_build_not_reached();
>  #endif

Should this change be in a different patch? It doesn't
seem related to the meson detection.



Otherwise
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>

thanks
-- PMM