Re: [Qemu-devel] [RFC PATCH 1/3] tcg/aarch64: Introduce and use jump to register

[Richard Henderson <rth@twiddle.net>]

On 06/07/2017 03:52 PM, Pranith Kumar wrote:
> Signed-off-by: Pranith Kumar <bobby.prani@gmail.com>
> ---
>   tcg/aarch64/tcg-target.inc.c | 10 ++++++++--
>   1 file changed, 8 insertions(+), 2 deletions(-)
> 
> diff --git a/tcg/aarch64/tcg-target.inc.c b/tcg/aarch64/tcg-target.inc.c
> index 1fa3bccc89..ab0a8caa03 100644
> --- a/tcg/aarch64/tcg-target.inc.c
> +++ b/tcg/aarch64/tcg-target.inc.c
> @@ -819,6 +819,12 @@ static inline void tcg_out_goto(TCGContext *s, tcg_insn_unit *target)
>       tcg_out_insn(s, 3206, B, offset);
>   }
>   
> +static inline void tcg_out_goto_register(TCGContext *s, intptr_t target)
> +{
> +    tcg_out_movi(s, TCG_TYPE_I64, TCG_REG_TMP, target);
> +    tcg_out_insn(s, 3207, BR, TCG_REG_TMP);
> +}
> +
>   static inline void tcg_out_goto_noaddr(TCGContext *s)
>   {
>       /* We pay attention here to not modify the branch target by reading from
> @@ -1364,10 +1370,10 @@ static void tcg_out_op(TCGContext *s, TCGOpcode opc,
>       case INDEX_op_exit_tb:
>           /* Reuse the zeroing that exists for goto_ptr.  */
>           if (a0 == 0) {
> -            tcg_out_goto(s, s->code_gen_epilogue);
> +            tcg_out_goto_register(s, (intptr_t)(s->code_gen_epilogue));

This pessimises the first 128MB of the buffer by not using a direct branch when 
it fits.  I think you should call the new function tcg_out_goto_long, and 
structure the function like tcg_out_call.


r~