Re: [Qemu-devel] [PATCH 16/35] tcg-s390: Re-implement tcg_out_movi.

[Richard Henderson]

On 06/12/2010 05:04 AM, Aurelien Jarno wrote:
>> +    for (i = 0; i < 4; i++) {
>> +        tcg_target_long mask = 0xffffull << i*16;
>> +        if ((uval & mask) != 0 && (uval & ~mask) == 0) {
> 
> Wouldn't it be simpler to use (uval & mask) == uval ?

Doh.

>> +    /* Try for PC-relative address load.  */
>> +    if ((sval & 1) == 0) {
>> +        intptr_t off = (sval - (intptr_t)s->code_ptr) >> 1;
>> +        if (off == (int32_t)off) {
>> +            tcg_out_insn(s, RIL, LARL, ret, off);
>> +            return;
>> +        }
>> +    }
> 
> Is this part used in practice? There was such a trick on the ARM
> backend, but it was actually never used.

Yes.  The difference here is we have a +- 4GB displacement.

This is primarily used when the extended-immediate facility is not present;
we can generate all even 32-bit constants from LARL, given the placement of
the code_gen_buffer.


r~