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

[Richard Henderson <rth@twiddle.net>]

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;
     }

     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.


r~