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

[Richard Henderson]

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~