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 Developersâ 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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