RE: [PATCH] Support APX NF

["Cui, Lili" <lili.cui@intel.com>]

> -----Original Message-----
> From: Jan Beulich <jbeulich@suse.com>
> Sent: Thursday, February 29, 2024 10:12 PM
> To: Cui, Lili <lili.cui@intel.com>
> Cc: Lu, Hongjiu <hongjiu.lu@intel.com>; binutils@sourceware.org
> Subject: Re: [PATCH] Support APX NF
> 
> On 29.02.2024 14:47, Cui, Lili wrote:
> >>>> -----Original Message-----
> >>>> From: Jan Beulich <jbeulich@suse.com>
> >>>> Sent: Thursday, February 29, 2024 8:04 PM
> >>>> To: Cui, Lili <lili.cui@intel.com>
> >>>> Cc: Lu, Hongjiu <hongjiu.lu@intel.com>; binutils@sourceware.org
> >>>> Subject: Re: [PATCH] Support APX NF
> >>>>
> >>>> On 29.02.2024 13:00, Cui, Lili wrote:
> >>>>>> On 27.02.2024 10:01, Cui, Lili wrote:
> >>>>>>> @@ -8860,6 +8880,9 @@ match_template (char mnem_suffix)
> >>>>>>>  		  goto check_operands_345;
> >>>>>>>  		}
> >>>>>>>  	      else if (t->opcode_space != SPACE_BASE
> >>>>>>> +		       /* Map0 and map1 are promoted to MAP4 when
> NF is
> >>>>>> enabled.
> >>>>>>> +			*/
> >>>>>>> +		       && !t->opcode_modifier.nf
> >>>>>>>  		       && (t->opcode_space != SPACE_0F
> >>>>>>>  			   /* MOV to/from CR/DR/TR, as an exception,
> follow
> >>>>>>>  			      the base opcode space encoding model.  */
> >>>>>>
> >>>>>> I don't understand this: How does a template permitting NF matter
> here?
> >>>>>> I could see the immediately preceding "else if" become something
> >>>>>> along the lines of
> >>>>>>
> >>>>>> 	      else if (is_cpu (t, CpuAPX_F) && (i.operands == 3 ||
> >>>>>> i.has_nf))
> >>>>>>
> >>>>>> But I admit I didn't fully think this through. It's just that the
> >>>>>> change as is looks wrong to me.
> >>>>>>
> >>>>>
> >>>>> I was also dissatisfied with this place yesterday and then modified it to:
> >>>>>
> >>>>>               else if (t->opcode_space != SPACE_BASE
> >>>>>                        /* For EVEX-promoted instructions, opcode_space is
> >>>>>                           promoted to MAP4.  */
> >>>>>                        && (t->opcode_space != SPACE_EVEXMAP4
> >>>>>                            || t->mnem_off == MN_movbe)
> >>>>>                        && (t->opcode_space != SPACE_0F
> >>>>>                            /* MOV to/from CR/DR/TR, as an exception, follow
> >>>>>                               the base opcode space encoding model.  */
> >>>>>                            || (t->base_opcode | 7) != 0x27))
> >>>>>
> >>>>> For EVEX-promoted instructions, opcode_space is promoted to MAP4.
> >>>>> The
> >>>> old judgment no longer fit for EVEX promoted instructions. However,
> >>>> the logic of this place is still not good.
> >>>>
> >>>> So what about my suggestion?
> >>>
> >>> Your suggestion is better, but we need to replace i.has_nf with new
> >> judgment, i.has_nf cannot cover instructions like adc, the testcase
> >> will be added by another patch.
> >>>
> >>> +             else if (is_cpu (t, CpuAPX_F)
> >>> +                      && (i.operands == 3 || (t->opcode_space ==
> SPACE_EVEXMAP4
> >>> +                                              && t->mnem_off !=
> >>> + MN_movbe)))
> >>
> >> Ah yes, to cover the non-NF 2-operand forms. But then is the
> >> "i.operands == 3"
> >> part actually still needed?
> >
> > It can be removed,  great suggestion, thanks!
> 
> Thinking of it - the is_cpu() then likely is unnecessary as well. If new
> map4 insn appeared that have D set in the template, they would likely follow
> the same pattern, yet be keyed to a different CPU feature. What's less clear is
> whether instead of special-casing MOVBE it would make sense to check the
> template's W bit here. Thoughts?
> 
> Jan

Yes, now all MAP4 instructions belong to APX, "is_cpu(t,CpuAPX_F)" is indeed redundant, 

For " else if (t->opcode_space == SPACE_EVEXMAP4 && t->opcode_modifier.w)"

Among all instructions of map2 and map3, only crc32 supports W, and it does not have "D". It can work. But when new instructions appear, these rules may be broken. I have no idea about this place. Maybe MOVBE is more intuitive? W's judgment is a high-level summary, perhaps more difficult to understand?

Thanks,
Lili.