Re: [Qemu-devel] [PATCH v21 4/7] target/avr: Add instruction translation

[Richard Henderson]

On 6/6/19 12:30 PM, Michael Rolnik wrote:
> +        if (ctx.check_skip > 0) {
> +            TCGLabel *skip = gen_new_label();
> +            TCGLabel *done = gen_new_label();
> +
> +            tcg_gen_brcondi_tl(TCG_COND_NE, cpu_skip, 0, skip);
> +                translate(&ctx);
> +                tcg_gen_br(done);
> +            gen_set_label(skip);
> +                tcg_gen_movi_tl(cpu_skip, 0);
> +                tcg_gen_movi_tl(cpu_pc, ctx.npc);
> +            gen_set_label(done);
> +            ctx.check_skip--;
> +        } else {
> +            translate(&ctx);
> +        }

In future, do not indent code like this.

I had been thinking of a slightly more complex solution that does not require
every TB to begin with a conditional branch testing cpu_skip.  This also has
the property that we almost never write to cpu_skip at all -- the condition is
consumed immediately within host registers without being written back to ENV.
The only time we do write to cpu_skip is for debugging, single-stepping, or
when we are forced to break the TB for other unusual reasons.

The following implements this solution.  It's based on some other cleanups that
I have made, and commented upon here.  The full tree can be found at

  https://github.com/rth7680/qemu/commits/review/avr-21


r~

0001-fixup-target-avr-Add-instruction-translation.patch
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