Re: [Qemu-devel] [PATCH RFC v1 1/3] target/ppc: Emulate LL/SC using cmpxchg helpers

[Nikunj A Dadhania]

Richard Henderson <address@hidden> writes:

> On 04/06/2017 03:22 AM, Nikunj A Dadhania wrote:
>> +    TCGv_i32 tmp = tcg_temp_local_new_i32();
>> +    TCGv t0;
>>
>> +    tcg_gen_movi_i32(tmp, 0);
>>      tcg_gen_trunc_tl_i32(cpu_crf[0], cpu_so);
>>      l1 = gen_new_label();
>>      tcg_gen_brcond_tl(TCG_COND_NE, EA, cpu_reserve, l1);
>> -    tcg_gen_ori_i32(cpu_crf[0], cpu_crf[0], CRF_EQ);
>> -    tcg_gen_qemu_st_tl(cpu_gpr[reg], EA, ctx->mem_idx, memop);
>> +
>> +    t0 = tcg_temp_new();
>> +    tcg_gen_atomic_cmpxchg_tl(t0, EA, cpu_reserve_val, cpu_gpr[reg],
>> +                              ctx->mem_idx, DEF_MEMOP(memop));
>> +    tcg_gen_setcond_tl(TCG_COND_EQ, t0, t0, cpu_reserve_val);
>> +    tcg_gen_trunc_tl_i32(tmp, t0);
>> +
>>      gen_set_label(l1);
>> +    tcg_gen_shli_i32(tmp, tmp, CRF_EQ_BIT);
>> +    tcg_gen_or_i32(cpu_crf[0], cpu_crf[0], tmp);
>
> I encourage you to move these two lines up beside the setcond.
> That way you don't need to use a local tmp, which implies a
> spill/restore from the stack.

Sure.

Regards
Nikunj