Baffling USE in x86_64.ad

[Vladimir Kozlov]

I agree that is not needed. We never cleaned up this before. I looked on history and it from 2000 when C2 was still in 
development.

Regards,
Vladimir


On 1/21/16 3:47 AM, Lindenmaier, Goetz wrote:
> Hi,
>
> adlc scans the match rule and derives USE/DEF effects from that.
> Then it adds in the effects from the effect() declaration, which are
> the same here.
>
> So that line is superfluous.
>
> (I once cleaned up the effects in the ppc
> port and removed all these.  And we are expand-power-users :) )
>
> Best regards,
>    Goetz.
>
>
>> -----Original Message-----
>> From: hotspot-compiler-dev [mailto:hotspot-compiler-dev-
>> bounces at openjdk.java.net] On Behalf Of Andrew Dinn
>> Sent: Donnerstag, 21. Januar 2016 11:30
>> To: Andrew Haley <aph at redhat.com>; hotspot compiler <hotspot-compiler-
>> dev at openjdk.java.net>
>> Subject: Re: Baffling USE in x86_64.ad
>>
>> On 21/01/16 10:22, Andrew Haley wrote:
>>> In this pattern:
>>>
>>> instruct compI_rReg(rFlagsReg cr, rRegI op1, rRegI op2)
>>> %{
>>>    match(Set cr (CmpI op1 op2));
>>>    effect(DEF cr, USE op1, USE op2);
>>>
>>>    format %{ "cmpl    $op1, $op2" %}
>>>    opcode(0x3B);  /* Opcode 3B /r */
>>>    ins_encode(REX_reg_reg(op1, op2), OpcP, reg_reg(op1, op2));
>>>    ins_pipe(ialu_cr_reg_reg);
>>> %}
>>>
>>> why does the USE appear in the effect?  And the DEF?  The operands
>>> appear in the match expression in the normal way, so I would have
>>> thought the effect expression unnecessary.  It's this pattern: others
>>> don't have the effect:
>>
>> I am not certain of this but I note that the above rule is used for
>> direct matching and also used for expansion. I believe the expansion
>> process requires an effect declaration even though that effect is also
>> implied by the match rule. There are many instruction definitions which
>> are only used for matching and they have an effect declaration but no
>> match declaration.
>>
>> regards,
>>
>>
>> Andrew Dinn
>> -----------
>> Senior Principal Software Engineer
>> Red Hat UK Ltd
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