Re: [patch, i386] false dependencies fix

[Jeff Law <law at redhat dot com>]

On 06/28/2018 01:16 AM, Uros Bizjak wrote:
> Hello!
> 
>>> --- i386.md (revision 259756)
>>> +++ i386.md (working copy)
>>> @@ -3547,7 +3547,7 @@
>>>   {
>>>   case MODE_DF:
>>>    if (TARGET_AVX && REG_P (operands[0]) && REG_P (operands[1]))
>>> -    return "vmovsd\t{%1, %0, %0|%0, %0, %1}";
>>> +    return "%vmovsd\t{%d1, %0|%0, %d1}";
>>>    return "%vmovsd\t{%1, %0|%0, %1}";
>>>
>>>   case MODE_V4SF:
>>> @@ -3748,7 +3748,7 @@
>>>   {
>>>   case MODE_SF:
>>>    if (TARGET_AVX && REG_P (operands[0]) && REG_P (operands[1]))
>>> -    return "vmovss\t{%1, %0, %0|%0, %0, %1}";
>>> +    return "%vmovss\t{%d1, %0|%0, %d1}";
>>>    return "%vmovss\t{%1, %0|%0, %1}";
>> So what I'm confused about is in the original output template operand 0
>> is duplicated. In the new template operand 1 is duplicated.
>>
>> Presumably what you're trying to accomplish is avoiding a false read on
>> operand 0 (the destination)?  Can you please confirm?
> 
>> Knowing that should also help me evaluate the changes to recp and rsqrt
>> since they're being changed to the same style encoding when operating
>> strictly on registers.
> 
> Please don't change "v" -> "%v" for TARGET_AVX templates. We know that
> in this case, all insn mnemonics are prefixed with "v".
ACK on that Uros -- I'd convinced myself that v->%v for TARGET_AVX
couldn't hurt anything since  we already had the v prefix in place.  I'm
happy to ensure this follows your preferred convention.

I was mostly trying to make sure I understood the other aspects of the
proposed change.

Cheers,
jeff