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From: Richard Henderson <richard.henderson@linaro.org>
Message-ID: <9ecb39e2-99e3-4d48-2582-8962005ed940@linaro.org>
Date: Fri, 12 Apr 2019 20:11:27 -1000
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Subject: Re: [Qemu-devel] [PATCH v1 37/41] s390x/tcg: Implement VECTOR
 SUBTRACT WITH BORROW COMPUTE BORROW INDICATION
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To: David Hildenbrand <david@redhat.com>, qemu-devel@nongnu.org
Cc: qemu-s390x@nongnu.org, Cornelia Huck <cohuck@redhat.com>, Thomas Huth <thuth@redhat.com>, Richard Henderson <rth@twiddle.net>

On 4/11/19 12:08 AM, David Hildenbrand wrote:
> +static DisasJumpType op_vsbcbi(DisasContext *s, DisasOps *o)
> +{
> +    if (get_field(s->fields, m5) != ES_128) {
> +        gen_program_exception(s, PGM_SPECIFICATION);
> +        return DISAS_NORETURN;
> +    }
> +
> +    gen_gvec_4_ool(get_field(s->fields, v1), get_field(s->fields, v2),
> +                   get_field(s->fields, v3), get_field(s->fields, v4), 0,
> +                   gen_helper_gvec_vsbcbi128);
> +    return DISAS_NEXT;
> +}


Reviewed-by: Richard Henderson <richard.henderson@linaro.org>

I'm sure this can be done similarly to add with carry compute carry, but it's
harder to reason with sub2.  Something like

	tcg_gen_andi_i64(tl, cl, 1);
	tcg_gen_sub2_i64(tl, th, al, zero, tl, zero);
	tcg_gen_sub2_i64(tl, th, tl, th, bl, zero);
	tcg_gen_andi_i64(tl, th, 1);
	tcg_gen_sub2_i64(tl, th, ah, zero, tl, zero);
	tcg_gen_sub2_i64(tl, th, tl, th, bh, zero);
	tcg_gen_andi_i64(tl, th, 1);
	/* result in tl */


r~