Re: [Qemu-devel] [PATCH 19/26] target-xtensa: implement loop option

[Max Filippov]

>> > +    if (env->sregs[LEND] != v) {
>> > +        tb_invalidate_phys_page_range(
>> > +                env->sregs[LEND] - 1, env->sregs[LEND], 0);
>> > +        env->sregs[LEND] = v;
>> > +        tb_invalidate_phys_page_range(
>> > +                env->sregs[LEND] - 1, env->sregs[LEND], 0);
>> > +    }
>>
>> Why are you invalidating twice?
>
> TB at the old LEND and at the new. Although it will work correctly without 
> first invalidation.
>
>> > +static void gen_check_loop_end(DisasContext *dc, int slot)
>> > +{
>> > +    if (option_enabled(dc, XTENSA_OPTION_LOOP) &&
>> > +            !(dc->tb->flags & XTENSA_TBFLAG_EXCM) &&
>> > +            dc->next_pc == dc->lend) {
>> > +        int label = gen_new_label();
>> > +
>> > +        tcg_gen_brcondi_i32(TCG_COND_NE, cpu_SR[LEND], dc->next_pc, 
>> > label);
>> > +        tcg_gen_brcondi_i32(TCG_COND_EQ, cpu_SR[LCOUNT], 0, label);
>> > +        tcg_gen_subi_i32(cpu_SR[LCOUNT], cpu_SR[LCOUNT], 1);
>> > +        gen_jump(dc, cpu_SR[LBEG]);
>> > +        gen_set_label(label);
>> > +        gen_jumpi(dc, dc->next_pc, slot);
>>
>> If you're going to pretend that LEND is a constant, you might as well
>> pretend that LBEG is also a constant, so that you get to chain the TB's
>> around the loop.
>
> But there may be three exits from TB at the LEND if its last command is a 
> branch: to the LBEG, to the branch target and to the next insn.

Ok, I guess that I need to add gen_wsr_lbeg that invalidates TB at the
current LEND, pretend that LBEG is constant and use given slot to jump
to it. And also to get rid of tcg_gen_brcondi_i32(TCG_COND_NE,
cpu_SR[LEND], dc->next_pc, label);

-- 
Thanks.
-- Max