[llvm-commits] [PATCH] TableGen backend support to express relations between instruction

[Jyotsna Verma]

Hello Jakob,

Here is the updated patch which includes a new section into
docs/WritingAnLLVMBackend.html and a high-level description of the algorithm
in CodeGenMapTable.cpp file.

Thanks,
Jyotsna

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> -----Original Message-----
> From: Jakob Stoklund Olesen [mailto:stoklund at 2pi.dk]
> Sent: Friday, September 28, 2012 4:42 PM
> To: Jyotsna Verma
> Cc: llvm-commits at cs.uiuc.edu
> Subject: Re: [llvm-commits] [PATCH] TableGen backend support to express
> relations between instruction
> 
> 
> On Sep 28, 2012, at 12:22 PM, Jyotsna Verma <jverma at codeaurora.org>
> wrote:
> 
> > Jakob,
> >
> >> In find the code very hard to read without a high-level description
> >> of
> > what it
> >> is supposed to do and how it is supposed to be used. Don't assume
> >> whoever reads the code has read any of the mailing list threads.
> >
> > I can understand that. I will include some description in the .cpp file.
> 
> Thanks.
> >
> > 1) Iterate through all the records that derive from "InstrMapping"
> > class
> > 2) For each record, we filter out instructions based on the
> > FilterClass value.
> > 3) Among this set, we look for the instructions that have the same
> > values as KeyCol for  all the fields listed in ColFields. These are
> > identified as the potential candidates for key instructions. Some of
> > these instructions may be dropped if their corresponding column
> > instruction is not found. In case of multi-column relation, the
> > instruction is removed if none of the relations are found.
> >
> > For Example:
> > def getPredOpcode : InstrMapping {
> >  let FilterClass = "PredRel";
> >    let RowFields = ["BaseOpcode"];
> >    let ColFields = ["PredSense"];
> >    let KeyCol = ["none"];
> >    let ValueCols = [["true"], ["false"]]; }
> >
> > Here, only instructions that have "none" as PredSense will be selected
> > as key instructions.
> >
> > 4) For each key instructions, we form a small group of instructions
> > which have the same values as the key instruction for all the fields
> > listed in RowFields.
> 
> OK, please avoid using a quadratic algorithm to do that.
> 
> > I don't know what you mean by the full backend. I'm not adding any new
> > TableGen option/flag for this functionality. I have just added the
> > functionality in a separate file and emit  output in GenInstrInfo.inc
> > file as you suggested. I call it after EmitInstrInfo function from
> > TableGen.cpp like this:
> 
> I see. I don't really understand the purpose of the MapTableEmitter class,
> then. There is very little class state, and you're passing a lot of
context
> around as function arguments.
> 
> /jakob

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