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Date: Thu, 05 Dec 2013 10:59:01 +1300
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Subject: Re: [Qemu-devel] [PATCH v2 12/12] target-arm: A64: add support for
 compare and branch imm
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To: Peter Maydell <peter.maydell@linaro.org>, qemu-devel@nongnu.org
Cc: patches@linaro.org, Michael Matz <matz@suse.de>, Alexander Graf <agraf@suse.de>, C Fontana <claudio.fontana@linaro.org>, Dirk Mueller <dmueller@suse.de>, Laurent Desnogues <laurent.desnogues@gmail.com>, kvmarm@lists.cs.columbia.edu

On 12/05/2013 08:33 AM, Peter Maydell wrote:
> +static TCGv_i64 read_cpu_reg(DisasContext *s, int reg, int sf)
> +{
> +    TCGv_i64 v = new_tmp_a64_zero(s);
> +    if (reg != 31) {

This is going to issue a garbage "movi tmp, 0" opcode for every non-XZR read.
While the optimizer will remove that, it's only going to slow things down, and
easily avoidable.

Better to allocate the temporary and only perform the movi for reg == 31.


r~