x86 FMA intrinsic support design

[Gilles Duboscq]

Hi Jean-Philippe,

Regarding `TernaryNode` you can introduce one if you want but this is not strictly necessary: there's no problem with your node directly sub-classing `FloatingNode`.

For `AMD64Ternary`, you can add it. You will indeed need a class with the correct amount of @Use and @Def fields. There might be some other "ternary" operations which use a specialized classes but this is some refactoring we can look at later.

  Gilles

On 13/04/2019 00:00, Halimi, Jean-Philippe wrote:
> Hi all,
> 
> Thanks a lot for your feedback. It has been two weeks, and I have made some progress, however it looks like the design shared earlier is incomplete. From what I can see, there are a few classes missing in Graal to allow the implementation.
> 
> 1. FusedMultiplyAddNode needs to extend a new TernaryNode.
> 2. AMD64ArithmeticLIRGenerator::emitFusedMultiplyAdd needs to be added, and I believe it needs a new AMD64Ternary class for code generation, to call the VexRVMOp.
> 	--> Here, I am not sure of whether AMD64Ternary is necessary, but I believe it is, since we are reading three values and writing back to the first one.
> 
> Do you believe this is the appropriate approach?
> 
> Thanks
> -Jp
> 
> -----Original Message-----
> From: graal-dev [mailto:graal-dev-bounces at openjdk.java.net] On Behalf Of Gilles Duboscq
> Sent: Friday, March 29, 2019 2:34 AM
> To: graal-dev at openjdk.java.net
> Subject: Re: x86 FMA intrinsic support design
> 
> Hi Jean-Philippe,
> 
> That sounds like a good plan!
> 
> In terms of naming, i would call such a node `FusedMultiplyAddNode`: spelling out what it does is much more important than the fact that it comes from an intrinsic.
> 
> Thanks,
>    Gilles
> 
> On 29/03/2019 01:04, Halimi, Jean-Philippe wrote:
>> Hello,
>>
>> I am currently looking into adding support for FMA intrinsics in Graal. I would like to share what I plan to do to make sure it is how it should be implemented.
>>
>>
>> 1.       Add VexRVMOp class support in AMD64Assembler with the corresponding FMA instructions
>>
>> a.       It requires to add the VexOpAssertion.FMA and CPUFeature.FMA flags
>>
>> 2.       Add UseFMA flag from HotSpot flags in GraalHotSpotVMConfig.java
>>
>> 3.       Add a registerFMA method in AMD64GraphBuilderPlugins::registerMathPlugins
>>
>> a.       This requires to add a specific FMAIntrinsicNode, which will emit the corresponding FMA instructions.
>>
>> Is there anything else that is needed in this case?
>>
>> Thanks for your insights,
>> Jp
>>