On 10/12/20 12:56 PM, Peter Maydell wrote:
> On Mon, 12 Oct 2020 at 16:37, Peter Maydell <peter.mayd...@linaro.org> wrote:
>>
>> v8.1M's "low-overhead-loop" extension has three instructions
>> for looping:
>> * DLS (start of a do-loop)
>> * WLS (start of a while-loop)
>> * LE (end of a loop)
>>
>> +static bool trans_WLS(DisasContext *s, arg_WLS *a)
>> +{
>> + /* M-profile low-overhead while-loop start */
>> + TCGv_i32 tmp;
>> + TCGLabel *nextlabel;
>> +
>> + if (!dc_isar_feature(aa32_lob, s)) {
>> + return false;
>> + }
>> + if (a->rn == 13 || a->rn == 15) {
>> + /* CONSTRAINED UNPREDICTABLE: we choose to UNDEF */
>> + return false;
>> + }
>> +
>> + nextlabel = gen_new_label();
>> + tcg_gen_brcondi_i32(TCG_COND_NE, cpu_R[a->rn], 0, nextlabel);
>> + gen_jmp(s, read_pc(s) + a->imm);
>> +
>> + gen_set_label(nextlabel);
>> + tmp = load_reg(s, a->rn);
>> + store_reg(s, 14, tmp);
>> + gen_jmp(s, s->base.pc_next);
>> + return true;
>> +}
>
> This turns out not to work, because gen_jmp() always generates
> a goto-tb for tb exit 0, and we hit the assert() that exit 0
> was not used twice. Here's a fixup to fold into this patch:
Indeed. I was going to suggest that here you should use arm_gen_condlabel()
like you did for LE. Which I think would be still cleaner than your fixup
patch.
r~
