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Re: [Qemu-devel] [PATCH v2] target-mips: simplify LWL/LDL mask generatio
From: |
Richard Henderson |
Subject: |
Re: [Qemu-devel] [PATCH v2] target-mips: simplify LWL/LDL mask generation |
Date: |
Thu, 23 Jul 2015 13:51:40 -0700 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.1.0 |
On 07/15/2015 08:05 AM, Aurelien Jarno wrote:
> The LWL/LDL instructions mask the GPR with a mask depending on the
> address alignement. It is currently computed by doing:
>
> mask = 0x7fffffffffffffffull >> (t1 ^ 63)
>
> It's simpler to generate it by doing:
>
> mask = ~(-1 << t1)
>
> It uses one TCG instruction less, and it avoids a 32/64-bit constant
> loading which can take a few instructions on RISC hosts.
>
> Cc: Leon Alrae <address@hidden>
> Signed-off-by: Aurelien Jarno <address@hidden>
> ---
> target-mips/translate.c | 14 ++++++--------
> 1 file changed, 6 insertions(+), 8 deletions(-)
>
> Changes v1 -> v2:
> - Use ~(-1 << t1) instead of (1 << t1) - 1 as suggested by Paolo
> Bonzini.
Reviewed-by: Richard Henderson <address@hidden>
r~