[llvm-dev] Re-using a node in a DAG output pattern in TableGen

[Cyril Six via llvm-dev]

Thank you! 


Cyril Six 
Compiler Engineer • Kalray 
Phone: 
csix at kalrayinc.com • [ https://www.kalrayinc.com/ | www.kalrayinc.com ] 

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From: "Jason Eckhardt" <jeckhardt at nvidia.com> 
To: "llvm-dev" <llvm-dev at lists.llvm.org>, "Cyril Six" <csix at kalrayinc.com> 
Sent: Monday, November 8, 2021 4:31:17 PM 
Subject: Re: Re-using a node in a DAG output pattern in TableGen 

You might give OutPatFrag a try: 

// OutPatFrag is a pattern fragment that is used as part of an output pattern 
// (not an input pattern). These do not have predicates or transforms, but are 
// used to avoid repeated subexpressions in output patterns. 
class OutPatFrag<dag ops, dag frag> 
: PatFrag<ops, frag, [{}], NOOP_SDNodeXForm>; 



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From: llvm-dev <llvm-dev-bounces at lists.llvm.org> on behalf of Cyril Six via llvm-dev <llvm-dev at lists.llvm.org> 
Sent: Monday, November 8, 2021 6:37 AM 
To: llvm-dev <llvm-dev at lists.llvm.org> 
Subject: [llvm-dev] Re-using a node in a DAG output pattern in TableGen 
External email: Use caution opening links or attachments 
Hello, 

I currently have an instruction selection pattern that looks like this : 




def : Pat<myinputop type:$v0 type:$v1, 
(COMPNHQ 
(ADDHQrr 
(SLLHQSri $v0, 8), 
(SLLHQSri $v1, 8), 
), 
(SLLHQSri $v0, 8), 
comparison_ltu 
)>; 



This output pattern is supposed to be a DAG: the node (SLLHQSri $v0, 8) is used two times. 

Experimentally, TableGen seems to recognize it as such (the node `(SLLHQSri $v0, 8)` will not be duplicated). 

I am wondering if there is a way to avoid having to repeat (SLLHQSri $v0, 8) in the syntax of TableGen, something like: 

BQ_BEGIN

def : Pat<inputpattern type:$v0 type:$v1, 
(COMPNHQ 
(ADDHQrr 
(SLLHQSri $v0, 8):$myvar, 
(SLLHQSri $v1, 8), 
), 
$myvar, 
comparison_ltu 
)>; 

BQ_END

If I try this, I get the error "Node 'myvar' in output pattern but not input pattern". 

Does anyone know if there is a way to name nodes from an output pattern to produce a non-tree output DAG? 

Do you know of any existing pattern featuring output DAG that are not trees? 

Thanks 

Cyril Six 
Compiler Engineer • Kalray 
Phone: 
csix at kalrayinc.com • [ https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.kalrayinc.com%2F&data=04%7C01%7Cjeckhardt%40nvidia.com%7C1bf04ec61fbb4f4958a908d9a2b48d7d%7C43083d15727340c1b7db39efd9ccc17a%7C0%7C0%7C637719718619602934%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=RtINTAlB1bxfjgh9PqVW7J%2FZ6pXFOUPPlAWtyK70t2U%3D&reserved=0 | 
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