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References: <1458815961-31979-1-git-send-email-sergey.fedorov@linaro.org>
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From: Alex =?utf-8?Q?Benn=C3=A9e?= <alex.bennee@linaro.org>
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Date: Thu, 24 Mar 2016 15:36:14 +0000
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Subject: Re: [Qemu-devel] [PATCH 8/8] tcg: Clean up tb_jmp_unlink()
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To: sergey.fedorov@linaro.org
Cc: Sergey Fedorov <serge.fdrv@gmail.com>, Richard Henderson <rth@twiddle.net>, Peter Crosthwaite <crosthwaite.peter@gmail.com>, qemu-devel@nongnu.org, Paolo Bonzini <pbonzini@redhat.com>


sergey.fedorov@linaro.org writes:

> From: Sergey Fedorov <serge.fdrv@gmail.com>
>
> Unify the code of this function with tb_jmp_remove_from_list(). Making
> these functions similar improves their readability. Also this could be a
> step towards making this function thread-safe.
>
> Signed-off-by: Sergey Fedorov <serge.fdrv@gmail.com>
> Signed-off-by: Sergey Fedorov <sergey.fedorov@linaro.org>
> ---
>  translate-all.c | 20 ++++++++------------
>  1 file changed, 8 insertions(+), 12 deletions(-)
>
> diff --git a/translate-all.c b/translate-all.c
> index 8b4bfa713bf7..56c77a72773d 100644
> --- a/translate-all.c
> +++ b/translate-all.c
> @@ -962,25 +962,21 @@ static inline void tb_reset_jump(TranslationBlock *tb, int n)
>  /* remove any jumps to the TB */
>  static inline void tb_jmp_unlink(TranslationBlock *tb)
>  {
> -    uintptr_t tb1, tb2;
> +    TranslationBlock *tb1;
> +    uintptr_t *ptb;
>      unsigned int n1;
>
> -    tb1 = tb->jmp_list_first;
> +    ptb = &tb->jmp_list_first;
>      for (;;) {
> -        TranslationBlock *tmp_tb;
> -        n1 = tb1 & 3;
> +        n1 = *ptb & 3;
> +        tb1 = (TranslationBlock *)(*ptb & ~3);

I would hope the compiler saw through the duplicate indirect accesses
but maybe:

    uintptr_t *ptb, ntb;

and

    ntb = *ptb;
    n1 = ntb & 3;
    tb1 = (TranslationBlock *)(ntb & ~3);

would be clearer?

>          if (n1 == 2) {
>              break;
>          }
> -        tmp_tb = (TranslationBlock *)(tb1 & ~3);
> -        tb2 = tmp_tb->jmp_list_next[n1];
> -        tb_reset_jump(tmp_tb, n1);
> -        tmp_tb->jmp_list_next[n1] = (uintptr_t)NULL;
> -        tb1 = tb2;
> +        tb_reset_jump(tb1, n1);
> +        *ptb = tb1->jmp_list_next[n1];
> +        tb1->jmp_list_next[n1] = (uintptr_t)NULL;
>      }
> -
> -    assert(((uintptr_t)tb & 3) == 0);
> -    tb->jmp_list_first = (uintptr_t)tb | 2; /* fail safe */
>  }
>
>  /* invalidate one TB */

Otherwise:

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

--
Alex Bennée