x86: Add support for Intel AMX instructions

[Jan Beulich]

On 06.07.2020 05:36, Cui, Lili wrote:
> --- /dev/null
> +++ b/gas/testsuite/gas/i386/x86-64-amx-inval.s
> @@ -0,0 +1,14 @@
> +# Check for SIBMEM operand used in certain AMX instructions
> +
> +    .text
> +_start:
> +    tileloadd (%rip), %tmm1
> +    tileloaddt1 (%rip), %tmm1
> +    tilestored %tmm1, (%rip)
> +    tdpbssd %xmm1, %xmm2, %xmm3

You also want to check that errors result for any of

    tdpbssd %tmm1, %tmm1, %tmm0
    tdpbssd %tmm1, %tmm0, %tmm1
    tdpbssd %tmm0, %tmm1, %tmm1

(albeit I have to admit I don't really understand the first of the
restrictions - at least for square matrices both sources being the
same registers ought to be fine imo). Which in turn points out
that even right now the comment at the top of the file is already
stale.

I'd also recommend adding something like

    vaddps %tmm1, %tmm2, %tmm3

here or somewhere else; after all this is what I did suspect
might have passed without an error in the earlier version of the
patch.

Jan