llvm dev - Jul 2020 - [Beginner] Understanding Tablegen language

Is there a backend to Tablegen which can dump a map of pattern-to-matched
to instruction-to-be-generated?
--help doesn't seem to indicate anything like that.

On Tue, Jul 14, 2020 at 2:13 PM Rotate Right <rightrotate5 at gmail.com>
wrote:
> Thanks Matt and Thomas. I will go through them.
>
> On Tue, Jul 14, 2020, 1:35 PM Matt P. Dziubinski <matdzb at
gmail.com> wrote:
>
>> On 7/13/2020 21:30, Thomas Lively via llvm-dev wrote:
>> > Part of the problem is that ISel patterns are like their own DSL
inside
>> > the TableGen DSL, so keywords like "ins",
"outs", and "ops" aren't
>> > keywords at the TableGen level, but rather at the level of the
ISel
>> > system implemented with TableGen. Copying existing patterns and
reading
>> > the comments in Target.td and TargetSelectionDAG.td are the best
ways I
>> > know of learning how this works. I haven't seen a separate
guide,
>> > although it would be very cool if one existed.
>>
>> FWIW, there are also some third-party resources that may be of help:
>>
>> "Lessons in TableGen"
>> FOSDEM 2019; Nicolai Hähnle
>> https://fosdem.org/2019/schedule/event/llvm_tablegen/
>> Slides:
>>
>>
https://archive.fosdem.org/2019/schedule/event/llvm_tablegen/attachments/slides/3304/export/events/attachments/llvm_tablegen/slides/3304/tablegen.pdf
>>
>> Series:
>> - What has TableGen ever done for us?:
>>
>>
http://nhaehnle.blogspot.com/2018/02/tablegen-1-what-has-tablegen-ever-done.html
>> - Functional Programming:
>>
>>
http://nhaehnle.blogspot.com/2018/02/tablegen-2-functional-programming.html
>> - Bits: http://nhaehnle.blogspot.com/2018/02/tablegen-3-bits.html
>> - Resolving variables:
>>
http://nhaehnle.blogspot.com/2018/03/tablegen-4-resolving-variables.html
>> - DAGs: http://nhaehnle.blogspot.com/2018/03/tablegen-5-dags.html
>>
>> Some of the parts of TableGen used in SelectionDAG are in the backend
>> docs (e.g., the keywords OP asked about):
>> https://llvm.org/docs/WritingAnLLVMBackend.html#instruction-set
>> &
https://llvm.org/docs/WritingAnLLVMBackend.html#instruction-selector
>> (has a simple example of `PatFrag` for `store`).
>>
>> There are a few examples of simple .td files an LLVM backend in the
>> following:
>>
>> LLVM backend development by example (RISC-V)
>> 2018 LLVM Developers’ Meeting; Alex Bradbury
>> https://www.youtube.com/watch?v=AFaIP-dF-RA
>>
>> 2014 - Building an LLVM Backend - LLVM Developer's Meeting
>> https://llvm.org/devmtg/2014-10/#tutorial1
>>
https://llvm.org/devmtg/2014-10/Slides/Cormack-BuildingAnLLVMBackend.pdf
>>
>>
https://llvm.org/devmtg/2014-04/PDFs/Talks/Building%20an%20LLVM%20backend.pdf
>>
>>
http://web.archive.org/http://llvm.org/devmtg/2014-10/Videos/Building%20an%20LLVM%20backend-720.mov
>> http://llvm.org/devmtg/2014-10/#tutorial1
>>
>>
http://www.inf.ed.ac.uk/teaching/courses/ct/other/LLVMBackend-2015-03-26_v2.pdf
>>
>> llvm-leg: LEG Example Backend
>> LEG Example Backend: a simple example LLVM backend for an ARM-like
>> architecture: 'LEG'.
>> https://github.com/frasercrmck/llvm-leg
>>
>> Best,
>> Matt
>>
>
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> On Jul 15, 2020, at 13:33, Rotate Right via llvm-dev <llvm-dev at
lists.llvm.org> wrote:
> 
> Is there a backend to Tablegen which can dump a map of pattern-to-matched
to instruction-to-be-generated?
> --help doesn't seem to indicate anything like that.

If you run tablgen with no arguments, it produces the fully expanded tablegen.
You can directly view what ends up getting interpreted there

-Matt

Adding -debug to a -gen-dag-isel run can also print useful information
about the parsed patterns.

On Wed, Jul 15, 2020 at 10:44 AM Matt Arsenault via llvm-dev <
llvm-dev at lists.llvm.org> wrote:
>
>
> > On Jul 15, 2020, at 13:33, Rotate Right via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
> >
> > Is there a backend to Tablegen which can dump a map of
> pattern-to-matched to instruction-to-be-generated?
> > --help doesn't seem to indicate anything like that.
>
>
> If you run tablgen with no arguments, it produces the fully expanded
> tablegen. You can directly view what ends up getting interpreted there
>
> -Matt
> _______________________________________________
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> llvm-dev at lists.llvm.org
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