[LLVMdev] TableGen backend support to express relations between instruction

[Hal Finkel]

On Tue, 28 Aug 2012 14:11:36 -0500
"Jyotsna Verma" <jverma at codeaurora.org> wrote:

> 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! This functionality can also be used in the PowerPC backend to
match load/store instructions to their 'with update' forms, and that
would be useful.

 -Hal

> 
> 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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> > LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> > http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
> 
> 
> 
> --
> Hal Finkel
> Postdoctoral Appointee
> Leadership Computing Facility
> Argonne National Laboratory
> 



-- 
Hal Finkel
Postdoctoral Appointee
Leadership Computing Facility
Argonne National Laboratory