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Re: [Xen-devel] [PATCH v2 1/6] x86emul: fix FMA scalar operand sizes


  • To: Jan Beulich <JBeulich@xxxxxxxx>, xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
  • From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
  • Date: Mon, 3 Sep 2018 17:43:39 +0100
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  • Delivery-date: Mon, 03 Sep 2018 16:44:05 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
  • Openpgp: preference=signencrypt

On 29/08/18 15:23, Jan Beulich wrote:
> FMA insns, other than the earlier AVX additions, don't use the low
> opcode bit to distinguish between single and double vector elements.

I think I've worked out why "other than the" is so weird to read as a
native speaker here.  I think you mean "unlike the" in this context.

> While the difference is benign for packed flavors, the scalar ones
> need to use VEX.W here. Oddly enough the table entries didn't even use
> simd_scalar_fp, but uniformly used simd_packed_fp (implying the
> distinction was by [VEX-encoded] opcode prefix).

Was this a bug in the FMA patch then?

>
> Split simd_scalar_fp into simd_scalar_opc and simd_scalar_vexw, and
> correct 

Missing the rest of the sentence?  (v1 was similar)

>
> Also correct the scalar insn comments (they only ever use XMM registers
> as operands).
>
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

As for the code content, Reviewed-by: Andrew Cooper
<andrew.cooper3@xxxxxxxxxx>

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