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From: Richard Henderson <rth@twiddle.net>
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Date: Fri, 12 May 2017 19:13:47 -0700
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Subject: Re: [Qemu-devel] [PATCH] tcg: optimize gen_extr_i64_i32()
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To: =?UTF-8?Q?Philippe_Mathieu-Daud=c3=a9?= <f4bug@amsat.org>, qemu-devel@nongnu.org, Aurelien Jarno <aurelien@aurel32.net>, Eric Blake <eblake@redhat.com>, Markus Armbruster <armbru@redhat.com>

On 05/12/2017 05:29 PM, Philippe Mathieu-Daudé wrote:
> Inspired by Richard Henderson comment:
> 
>      http://lists.nongnu.org/archive/html/qemu-devel/2017-05/msg02277.html
> 
> Patch applied mechanically with this coccinelle semantic patch:
> 
>      @@
>      expression lo, hi,arg;
>      @@
>      -tcg_gen_extrl_i64_i32(lo, arg);
>      -tcg_gen_extrh_i64_i32(hi, arg);
>      +tcg_gen_extr_i64_i32(lo, hi, arg);
> 
> Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
> ---
>   tcg/tcg-op.c | 3 +--
>   1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/tcg/tcg-op.c b/tcg/tcg-op.c
> index 6b1f41500c..f3d556c21a 100644
> --- a/tcg/tcg-op.c
> +++ b/tcg/tcg-op.c
> @@ -2562,8 +2562,7 @@ void tcg_gen_extr_i64_i32(TCGv_i32 lo, TCGv_i32 hi, TCGv_i64 arg)
>           tcg_gen_mov_i32(lo, TCGV_LOW(arg));
>           tcg_gen_mov_i32(hi, TCGV_HIGH(arg));
>       } else {
> -        tcg_gen_extrl_i64_i32(lo, arg);
> -        tcg_gen_extrh_i64_i32(hi, arg);
> +        tcg_gen_extr_i64_i32(lo, hi, arg);

You've just created an instance of infinite self-recursion.


r~