[LLVMdev] TableGen backend support to express relations between instruction

[Jyotsna Verma]

Hi Hal,

I will try to explain the functionality using a simple example. Let's say
that we have three formats for 'ADD' instruction and we want to relate them.

ADD - non-predicated form
ADD_pt : predicate true
ADD_pf : predicate false

We can define the relationship between the non-predicated instructions and
their predicate formats as follows:

def getPredOpcode : InstrMapping { // InstrMapping is a new class defined in
Target.td

// Used to filter instructions that have this kind of relationship
let FilterClass = "PredRel";

// Instructions with the same BaseOpcode value form a row.
let RowFields = ["BaseOpcode"];

// Instructions with the same predicate sense form a column.
let ColFields = ["PredSense"];

// The key column is the unpredicated instructions.
let KeyCol = ["nopred"];

// Value columns are PredSense=true and PredSense=false
  let ValueCols = [["true"], ["false"]];
}

Instructions need to set some fields in order for the TableGen to relate
them using the information provided in 'getPredOpcode'. 

Def ADD: PredRel {
   let BaseOpcode = "ADD";
   let PredSense = "nopred";
}

Def ADD_pt: PredRel {
   let BaseOpcode = "ADD";
   let PredSense = "true";
}

Def ADD_pf: PredRel {
   let BaseOpcode = "ADD";
   let PredSense = "false";
}

Here, BaseOpcode and PredSense are the new fields added to the (Hexagon)
Instructions. Other targets can define their own relations and add new
fields if necessary. TableGen will output relations as a table which can be
queried using a function  

getPredOpcode(Opcode, predsense) {
If (predsense == true)
  return getPredOpcodeTable[Opcode][0]
if (predsense == false)
  return getPredOpcodeTable[Opcode][1]
}
 
Let me know if something is not clear and I will try to explain it further.

Thanks,
Jyotsna
--
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum.


-----Original Message-----
From: Hal Finkel [mailto:hfinkel at anl.gov] 
Sent: Tuesday, August 28, 2012 1:27 PM
To: Jyotsna Verma
Cc: 'Jakob Stoklund Olesen'; llvmdev at cs.uiuc.edu
Subject: Re: [LLVMdev] TableGen backend support to express relations between
instruction

Jyotsna,

I hadn't been following this, so I apologize if this has already been
provided, but can you give a quick example of how this functionality is
used?

Thanks in advance,
Hal

On Tue, 28 Aug 2012 13:01:17 -0500
"Jyotsna Verma" <jverma at codeaurora.org> wrote:

> Hi Jakob,
> 
> Here is the first draft of the patch to add TableGen backend support 
> for the instruction mapping tables. Please take a look and let me know 
> your suggestions. As of now, I create one mapping table per relation 
> which results into a long .inc file. So, I'm planning to combine 
> everything into a single table and will include APIs (one per
> relation) to query from this table. 
> 
> Thanks,
> Jyotsna
> --
> Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum.
> 
> 
> -----Original Message-----
> From: llvmdev-bounces at cs.uiuc.edu
> [mailto:llvmdev-bounces at cs.uiuc.edu] On Behalf Of Jyotsna Verma
> Sent: Tuesday, August 21, 2012 12:42 PM
> To: 'Jakob Stoklund Olesen'
> Cc: llvmdev at cs.uiuc.edu
> Subject: Re: [LLVMdev] TableGen related question for the Hexagon 
> backend
> 
> Sounds good. I've started adding TableGen backend support to emit 
> relationship table into a .inc file. Hoping to finish it soon.
> 
> Thanks for all your help.
> 
> -Jyotsna
> --
> Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum.
> 
> 
> -----Original Message-----
> From: Jakob Stoklund Olesen [mailto:stoklund at 2pi.dk]
> Sent: Tuesday, August 21, 2012 11:28 AM
> To: Jyotsna Verma
> Cc: llvmdev at cs.uiuc.edu
> Subject: Re: [LLVMdev] TableGen related question for the Hexagon 
> backend
> 
> 
> On Aug 20, 2012, at 9:22 PM, Jyotsna Verma <jverma at codeaurora.org>
> wrote:
> 
> > Jakob,
> > 
> > One more question. You had suggested 'ValueCols' as of type 
> > list<list<string> >. Does the TableGen know how to extract it? It 
> > appears to me that we may have to add support for that.
> 
> You just start from getValueAsListInit() and go from there.
> 
> /jakob
> 
> 
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--
Hal Finkel
Postdoctoral Appointee
Leadership Computing Facility
Argonne National Laboratory