Re: [Qemu-devel] Shifts, ppc[64], xtensa

[malc <av1474@comtv.ru>]

On Thu, 20 Sep 2012, Max Filippov wrote:

> On Wed, Sep 19, 2012 at 11:53 PM, Richard Henderson <rth@twiddle.net> wrote:
> > On 09/19/2012 11:30 AM, Peter Maydell wrote:
> >> ...but on the other hand that ought to work for PPC too, so
> >> presumably my analysis is wrong somewhere.
> >
> > It isn't.  It's a target-xtensa bug.
> >

[..snip..]

> 
> This code is generated when TB ends on LEND
> (zero-overhead loop ending) with branching instruction.
> So, in addition to 3 way branch there's extra looping code
> generated by unconditional gen_check_loop_end(dc, 0);
> at the end of disas_xtensa_insn. I was pretty sure that this
> dead code would make no harm. --enable-debug-tcg says
> nothing on x86_64 host. The following should fix that:

It does, once the commit message is fixed i can apply it.

> 
> -- >8 --
> From: Max Filippov <jcmvbkbc@gmail.com>
> Date: Thu, 20 Sep 2012 04:07:20 +0400
> Subject: [PATCH] target-xtensa: don't emit extra gen_check_loop_end
> 
> Unconditional gen_check_loop_end at the end of disas_xtensa_insn
> can emit tcg_gen_goto_tb with slot id already used in the TB (e.g. when
> TB ends at LEND with a branch). Not all tcg backends can handle that.
> 
> Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
> ---
>  target-xtensa/translate.c |    4 +++-
>  1 files changed, 3 insertions(+), 1 deletions(-)
> 
> diff --git a/target-xtensa/translate.c b/target-xtensa/translate.c
> index 63b37b3..57a2b6f 100644
> --- a/target-xtensa/translate.c
> +++ b/target-xtensa/translate.c
> @@ -2502,7 +2502,9 @@ static void disas_xtensa_insn(DisasContext *dc)
>          break;
>      }
> 
> -    gen_check_loop_end(dc, 0);
> +    if (dc->is_jmp == DISAS_NEXT) {
> +        gen_check_loop_end(dc, 0);
> +    }
>      dc->pc = dc->next_pc;
> 
>      return;
> 

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