Re: [Qemu-devel] [PATCH 2/4] tcg/aarch64: implement new TCG target for aarch64

[Claudio Fontana]

On 27.05.2013 20:47, Richard Henderson wrote:
> On 2013-05-27 04:43, Claudio Fontana wrote:
>>> Hmm, true.  Although I'd been thinking more along the lines of
>>> arranging the code such that we'd use movz to set the zero.
>>
>> I think we need to keep treating zero specially if we want to keep the 
>> optimization where we don't emit needless MOVK instructions for half-words 
>> of value 0000h.
>>
>> I can however make one single function out of movi32 and movi64, it could 
>> look like this:
>>
>> if (!value) {
>>      tcg_out_movr(s, 0, rd, TCG_REG_ZXR);
>>      return;
>> }
>>
>> base = (value > 0xffffffff) ? 0xd2800000 : 0x52800000;
>>
>> while (value) {
>>      /* etc etc */
>> }
> 
> 
>     if (type == TCG_TYPE_I32) {
>         value = (uint32_t)value;
>         ext = 0;
>     } else if (value <= 0xffffffff) {
>         ext = 0;
>     } else {
>         ext = 0x80000000;
>     }

The check for type is probably unnecessary, since we don't gain anything (we 
still have to check something once), so I'd rather use a uint64_t parameter and 
then just check for value < 0xffffffff.

> 
>     base = 0x52800000;  /* MOVZ */
>     do {
>         int shift = ctz64(value) & (63 & -16);
>         int half = (value >> shift) & 0xffff;
>         tcg_out32(s, base | ext | half << 5 | rd);
>         value &= ~(0xffffUL << shift);
>         base = 0x72800000;  /* MOVK */
>     } while (value != 0);
> 
> 
> Since we go through the loop at least once, we emit the movz for zero input. 
> No need for any extra tests.  And using ctz we can iterate fewer times.

Of course, doh. I'll make use of do..while. 

Thanks,

Claudio