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References: <20180805182832.3012-1-pavel.zbitskiy@gmail.com>
	<20180805182832.3012-4-pavel.zbitskiy@gmail.com>
From: Richard Henderson <richard.henderson@linaro.org>
Message-ID: <15c06ae1-5262-85fe-df70-afd570f7efa7@linaro.org>
Date: Mon, 6 Aug 2018 08:24:44 -0700
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Subject: Re: [Qemu-devel] [PATCH 3/6] target/s390x: fix ipm polluting
 irrelevant bits
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To: Pavel Zbitskiy <pavel.zbitskiy@gmail.com>, qemu-devel@nongnu.org
Cc: David Hildenbrand <david@redhat.com>, qemu-trivial@nongnu.org, Cornelia Huck <cohuck@redhat.com>, Alexander Graf <agraf@suse.de>, "open list:S390" <qemu-s390x@nongnu.org>, Richard Henderson <rth@twiddle.net>

On 08/05/2018 11:28 AM, Pavel Zbitskiy wrote:
> +    tcg_gen_andi_i64(t1, psw_mask, 0x00000f0000000000);
> +    tcg_gen_shri_i64(t1, t1, 16);

It would be better to swap these two operations, so that a 64-bit constant
isn't needed for the mask, e.g:

    tcg_gen_shri_i64(t1, psw_mask, 16);
    tcg_gen_andi_i64(t1, t1, 0xf000000);

Or maybe rewrite this whole function with extract/deposit:

    tcg_gen_extract_i64(t1, psw_mask, 40, 4);
    tcg_gen_extu_i32_i64(t2, cc_op);
    tcg_gen_deposit_i64(t1, t1, t2, 4, 60);
    tcg_gen_deposit_i64(o->out, o->out, t1, 24, 8);

But what you have is not wrong so,
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>


r~