Re: [Qemu-devel] [PATCH v2 1/5] tcg: Refactor helper_lookup_tb_ptr

["Alex Bennée" <alex.bennee@linaro.org>]

Richard Henderson <rth@twiddle.net> writes:

> We can call tb_htable_lookup even when the tb_jmp_cache
> is completely empty.  Therefore, un-nest most of the code
> dependent on tb != NULL from the read from the cache.
>
> Signed-off-by: Richard Henderson <rth@twiddle.net>

Reviewed-by: Alex Bennée <alex.bennee@linaro.org>

> ---
>  tcg-runtime.c | 34 ++++++++++++++++++----------------
>  1 file changed, 18 insertions(+), 16 deletions(-)
>
> diff --git a/tcg-runtime.c b/tcg-runtime.c
> index 7fa90ce..a35c725 100644
> --- a/tcg-runtime.c
> +++ b/tcg-runtime.c
> @@ -147,30 +147,32 @@ uint64_t HELPER(ctpop_i64)(uint64_t arg)
>  void *HELPER(lookup_tb_ptr)(CPUArchState *env, target_ulong addr)
>  {
>      CPUState *cpu = ENV_GET_CPU(env);
> +    void *ret = tcg_ctx.code_gen_epilogue;
>      TranslationBlock *tb;
>      target_ulong cs_base, pc;
> -    uint32_t flags;
> -
> -    tb = atomic_rcu_read(&cpu->tb_jmp_cache[tb_jmp_cache_hash_func(addr)]);
> -    if (likely(tb)) {
> -        cpu_get_tb_cpu_state(env, &pc, &cs_base, &flags);
> -        if (likely(tb->pc == addr && tb->cs_base == cs_base &&
> -                   tb->flags == flags)) {
> -            goto found;
> -        }
> +    uint32_t flags, addr_hash;
> +
> +    addr_hash = tb_jmp_cache_hash_func(addr);
> +    tb = atomic_rcu_read(&cpu->tb_jmp_cache[addr_hash]);
> +    cpu_get_tb_cpu_state(env, &pc, &cs_base, &flags);
> +
> +    if (unlikely(!(tb
> +                   && tb->pc == addr
> +                   && tb->cs_base == cs_base
> +                   && tb->flags == flags))) {
>          tb = tb_htable_lookup(cpu, addr, cs_base, flags);
> -        if (likely(tb)) {
> -            atomic_set(&cpu->tb_jmp_cache[tb_jmp_cache_hash_func(addr)], tb);
> -            goto found;
> +        if (!tb) {
> +            return ret;
>          }
> +        atomic_set(&cpu->tb_jmp_cache[addr_hash], tb);
>      }
> -    return tcg_ctx.code_gen_epilogue;
> - found:
> +
> +    ret = tb->tc_ptr;
>      qemu_log_mask_and_addr(CPU_LOG_EXEC, addr,
>                             "Chain %p [%d: " TARGET_FMT_lx "] %s\n",
> -                           tb->tc_ptr, cpu->cpu_index, addr,
> +                           ret, cpu->cpu_index, addr,
>                             lookup_symbol(addr));
> -    return tb->tc_ptr;
> +    return ret;
>  }
>
>  void HELPER(exit_atomic)(CPUArchState *env)


--
Alex Bennée