Re: [PATCH v3 2/4] target/ppc: Add recording of taken branches to BHRB

[Nicholas Piggin]

On Tue Sep 26, 2023 at 3:43 AM AEST, Glenn Miles wrote:
> This commit continues adding support for the Branch History
> Rolling Buffer (BHRB) as is provided starting with the P8
> processor and continuing with its successors.  This commit
> is limited to the recording and filtering of taken branches.
>
> The following changes were made:
>
>   - Enabled functionality on P10 processors only due to
>     performance impact seen with P8 and P9 where it is not
>     disabled for non problem state branches.
>   - Added a BHRB buffer for storing branch instruction and
>     target addresses for taken branches
>   - Renamed gen_update_cfar to gen_update_branch_history and
>     added a 'target' parameter to hold the branch target
>     address and 'inst_type' parameter to use for filtering
>   - Added TCG code to gen_update_branch_history that stores
>     data to the BHRB and updates the BHRB offset.
>   - Added BHRB resource initialization and reset functions
>
> Signed-off-by: Glenn Miles <milesg@linux.vnet.ibm.com>
> ---

> +static inline void gen_update_branch_history(DisasContext *ctx,
> +                                             target_ulong nip,
> +                                             TCGv target,
> +                                             target_long inst_type)
>  {
>  #if defined(TARGET_PPC64)
> +    TCGv base;
> +    TCGv tmp;
> +    TCGv offset;
> +    TCGv mask;
> +    TCGLabel *no_update;
> +
>      if (ctx->has_cfar) {
>          tcg_gen_movi_tl(cpu_cfar, nip);
>      }
> +
> +    if (!ctx->has_bhrb ||
> +        !ctx->bhrb_enable ||
> +        inst_type == BHRB_TYPE_NORECORD) {
> +        return;
> +    }

BTW while debugging what turned out to be a mismerge, I removed has_bhrb
because bhrb_enable is always a subset. Shout if you have an objection.

Thanks,
Nick