Re: [PATCH 5/8] Support APX NDD optimized encoding.

[Jan Beulich <jbeulich@suse.com>]

On 24.10.2023 03:40, Hu, Lin1 wrote:
>> -----Original Message-----
>> From: Jan Beulich <jbeulich@suse.com>
>> Sent: Monday, October 23, 2023 4:15 PM
>>
>> On 23.10.2023 09:50, Hu, Lin1 wrote:
>>>> -----Original Message-----
>>>> From: Jan Beulich <jbeulich@suse.com>
>>>> Sent: Monday, October 23, 2023 3:24 PM
>>>>
>>>> On 23.10.2023 04:57, Hu, Lin1 wrote:
>>>>
>>>>> -----Original Message-----
>>>>> From: Jan Beulich <jbeulich@suse.com>
>>>>> Sent: Thursday, September 28, 2023 5:30 PM
>>>>>
>>>>> On 19.09.2023 17:25, Cui, Lili wrote:
>>>>>> --- a/gas/config/tc-i386.c
>>>>>> +++ b/gas/config/tc-i386.c
>>>>>> @@ -7091,6 +7091,46 @@ check_EgprOperands (const insn_template *t)
>>>>>>    return 0;
>>>>>>  }
>>>>>>
>>>>>> +/* Optimize APX NDD insns to non-NDD insns.  */
>>>>>> +
>>>>>> +static int
>>>>>
>>>>> "bool" please when the function merely returns a yes/no indicator.
>>>>>
>>>>> * Have modified.
>>>>>
>>>>>> +optimize_NDD_to_nonNDD (const insn_template *t) {
>>>>>> +  if (t->opcode_modifier.vexvvvv
>>>>>> +      && t->opcode_space == SPACE_EVEXMAP4
>>>>>> +      && i.reg_operands >= 2
>>>>>
>>>>> See the remark near the bottom of the changes to this file: This
>>>>> condition is likely insufficient, as
>>>>> - further insns allowing ND may not be treated this way (CCMPscc,
>>>>>   CTESTscc, and one of the CFCMOVcc forms at the very least),
>>>>> - {nf} uses will want excluding, as it would be merely a waste of
>>>>>   time to try to re-match with fewer operands.
>>>>>
>>>>> * CCMPSCC and CTESTSCC’s vexvvvv will be false. I think one of the
>>>> CFCMOVCC forms is same.
>>>>
>>>> By "is same" do you mean "fits the optimization pattern here"?
>>>>
>>>
>>> Because I didn't find any insn that allowing ND, but its vexvvvv is true in
>> CFCMOVcc's table. I'm going to assume that you found it, but I don't see it. I
>> believe its vexvvvv is false, too. So I say it is same as CCMPSCC and CTESTSCC.
>>
>> CFCMOVcc permits ND and uses EVEX.vvvv in one of its forms. It's unclear to me
>> whether it can be "optimized", though. In any event, I'd like to revisit the
>> condition here once this patch comes after all functional ones, so we (I) have a
>> clear picture of how all the insns are represented in the opcode table.
> 
> Oh, you are right. It seems that CFCMOVcc doesn't support this optimization from the instruction behavior. But CFCMOVcc support doesn't in this round of work. At the moment, I thinks we can use "i.has_nf && i.tm.opcode_modifier.nf" to exclude CFCMOVcc and other NF insns.

Well, as said before - imo it would be best if the optimization patch
came after all functional ones.

Jan