From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from eggs.gnu.org ([208.118.235.92]:46989)
	by lists.gnu.org with esmtp (Exim 4.71)
	(envelope-from <rth7680@gmail.com>) id 1Uh2SH-000406-GL
	for qemu-devel@nongnu.org; Mon, 27 May 2013 14:47:46 -0400
Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71)
	(envelope-from <rth7680@gmail.com>) id 1Uh2S8-0005xg-6f
	for qemu-devel@nongnu.org; Mon, 27 May 2013 14:47:37 -0400
Received: from mail-qe0-f51.google.com ([209.85.128.51]:51701)
	by eggs.gnu.org with esmtp (Exim 4.71)
	(envelope-from <rth7680@gmail.com>) id 1Uh2S8-0005xc-2O
	for qemu-devel@nongnu.org; Mon, 27 May 2013 14:47:28 -0400
Received: by mail-qe0-f51.google.com with SMTP id nd7so3840871qeb.24
	for <qemu-devel@nongnu.org>; Mon, 27 May 2013 11:47:27 -0700 (PDT)
Sender: Richard Henderson <rth7680@gmail.com>
Message-ID: <51A3AA3A.4050406@twiddle.net>
Date: Mon, 27 May 2013 11:47:22 -0700
From: Richard Henderson <rth@twiddle.net>
MIME-Version: 1.0
References: <5141F36E.10004@huawei.com> <519DCEC8.8060000@huawei.com>
	<519DD0BF.4090702@huawei.com> <519E43EE.6090702@twiddle.net>
	<519F2A8F.6090903@huawei.com> <519F9D11.9020603@twiddle.net>
	<51A346EC.2080005@huawei.com>
In-Reply-To: <51A346EC.2080005@huawei.com>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 7bit
Subject: Re: [Qemu-devel] [PATCH 2/4] tcg/aarch64: implement new TCG target
	for aarch64
List-Id: <qemu-devel.nongnu.org>
List-Unsubscribe: <https://lists.nongnu.org/mailman/options/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=unsubscribe>
List-Archive: <http://lists.nongnu.org/archive/html/qemu-devel>
List-Post: <mailto:qemu-devel@nongnu.org>
List-Help: <mailto:qemu-devel-request@nongnu.org?subject=help>
List-Subscribe: <https://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=subscribe>
To: Claudio Fontana <claudio.fontana@huawei.com>
Cc: Peter Maydell <peter.maydell@linaro.org>, Jani Kokkonen <Jani.Kokkonen@huawei.com>, qemu-devel@nongnu.org

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~