Re: [Qemu-devel] [PATCH 11/13] target-openrisc: use jmp_pc as flag variable for branches

[Richard Henderson <rth@twiddle.net>]

On 10/29/2013 12:04 PM, Sebastian Macke wrote:
>          {
>              int lab = gen_new_label();
> -            dc->btaken = tcg_temp_local_new();
> -            tcg_gen_movi_tl(jmp_pc, dc->pc+8);
> -            tcg_gen_movi_tl(dc->btaken, 0);
> +            tcg_gen_movi_tl(jmp_pc, 0);
>              tcg_gen_brcondi_i32(op0 == 0x03 ? TCG_COND_NE : TCG_COND_EQ,
>                                  cpu_srf, 0, lab);
> -            tcg_gen_movi_tl(dc->btaken, 1);
>              tcg_gen_movi_tl(jmp_pc, tmp_pc);
>              gen_set_label(lab);

You can now use movcond here:

  tcg_gen_movi_i32(jmp_pc, tmp_pc);
  tcg_gen_movcond_i32(jmp_pc, cpu_srf, zero, jmp_pc, zero,
                      op0 == 0x03 ? TCG_COND_NE : TCG_COND_EQ);

Although I'd wonder about just using setcond instead, since I think
the value stored in jmp_pc here is also stored in dc->j_target, leading
to the right behaviour...

>      case JUMP_BRANCH:
>          {
>              int l1 = gen_new_label();
> -            tcg_gen_brcondi_tl(TCG_COND_NE, dc->btaken, 0, l1);
> +            tcg_gen_brcondi_tl(TCG_COND_NE, jmp_pc, 0, l1);
>              gen_goto_tb(dc, 1, dc->pc);
>              gen_set_label(l1);
> -            tcg_temp_free(dc->btaken);
>              gen_goto_tb(dc, 0, dc->j_target);
>              break;

... here.

> +    case JUMP_BRANCH_DELAYED:
> +        {
> +            int l1 = gen_new_label();
> +            tcg_gen_brcondi_tl(TCG_COND_NE, jmp_pc, 0, l1);
> +            gen_goto_tb(dc, 1, dc->pc);
> +            gen_set_label(l1);
> +            tcg_gen_mov_tl(cpu_pc, jmp_pc);
> +            tcg_gen_exit_tb(0);
> +            break;
...
> +
> +    dc->delayed_branch = !!(dc->tb_flags & D_FLAG);
> +    if ((dc->delayed_branch) && (dc->tb_flags&B_FLAG)) {
> +        dc->j_state = JUMP_BRANCH_DELAYED;
> +    }
> +


And thus I can't see how these additions are actually useful?

If I've missed something, and the last hunk needs to be retained,
then please fix the coding style:

  if (dc->delayed_branch && (dc->tb_flags & B_FLAG)) {


r~