Weekly Progress Report: Building an LLVM Backend for PRU

Google Summer of Code
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Hello,
This is the weekly report for my GSoC project - Building an LLVM Backend for PRU.

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Hello Everyone! Here’s my Week 0 progress and the targets set for Week 1.

Tasks done in the Community Bonding Period - Week 0

  • Understood how to build a backend for a custom target in LLVM thoroughly.
  • Went through the PRU documentation, understood more about the hardware and it’s setup.
  • Submitted the Introductory Video.

Tasks for Week 1 - Conding Period Begins

  • Go through the PRU Assembly, compile some examples using pru-gcc.
  • Refer the Cpu0 backend, going through the codebase and implementation.
  • Read the PRU section of the reference manual, and understand more about it.

Suggestion given : Look for a way to take care of the special functions in the language, like gpio pins configuration, debugging functionality and so on

Final goal : Upstreaming the backend

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Week 1

Tasks done in Week 1:

  • Setting up BeagleBone Black
  • Implementing basic examples, pru-gcc examples on BBB
  • Read about PRU Assembly Instruction

Blockers:

  • Do not use “Flasher” Debian image.
  • LLVM version 12 not supported by the Cpu0 backend.

Week 2 target:

  • Get the Cpu0 Backend Running
  • Implement examples on the Cpu0 backend
  • Understand it’s codebase
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Week 2

Tasks done in Week 2:

  • Built the Cpu0 Backend using LLVM version 8
  • Implemented few examples
  • Understood the codebase, went through the tutorial

Blockers:
Invoke the llc built and do not use the system llc

Week 3 target:

  • Modify code for existing implementation of PRU backend
  • Write the registerinfo.td
  • Go through the PRU instructions thoroughly
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Week 3

Tasks done in Week 3:

  • Wrote the registerinfo.td (Tablegen file) for PRU
  • Went through the PRU Instruction set
  • Started working on the instrinfo.td for PRU
  • Started modifying the existing pru backend for lastest version of LLVM

Week 4 target:

  • Get done with instrinfo.td
  • Build the existing pru backend on LLVM version 16
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Week 4

Tasks done in Week 4:

  • Wrote the Instrinfo.td (Tablegen file) for PRU
  • Wrote the Instrformat.td (Tablegen file) for PRU

Blocker:
Instruction formats of few pru instructions like sbbo, lbbo
Existing pru backend files need to be changed completely according to new LLVM version format

Week 5 target:

  • Test the tablegen files
  • Graft the Registerinfo.td file into Cpu0 backend and test
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Week 5

Tasks done in Week 5:

  • Modified the registerinfo.td
  • Added type profiles and SD nodes to instrinfo.td
  • Worked on testing registerinfo.td by grafting in Cpu0 backend

Blockers:

Building the registerinfo.td by grafting in the Cpu0 backend, throws a lot of errors due to difference of the naming convention

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Week 6

Tasks done in Week 6:

  • Worked on building a basic framework for the PRU target in LLVM

  • Registering PRU as a target

  • Writing all the target files, register, instructions files for PRU

Blockers:

Facing some compilation errors while building the code, working on resolving them

Week 7 target:

Register PRU as a target successfully

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Week 7
Tasks done in Week 7:

  • Successfully registered PRU as a target in LLVM
  • Basic framework for PRU ready in the llvm source code

Week 8 target:
Work on all the files of PRU to be able to produce output for basic codes.

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Week 8:
Tasks done in Week 8:

  • Working on the Instruction files and IselLowering files
  • Completed chp1 and chp2.1 of the Cpu0 repo being referred

Blockers:
No resource for the instruction formats of PRU, so contacted a TI person through LLVM forum

Week 9 target:
Complete chp 2.2 and chp2.3 of the Cpu0 reference repo

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Week 9
Tasks done in Week 9:

  • Working on the framelowering, targetmachine and machinefunction info files
  • Completed chp2.2 and chp2.3 of the Cpu0 repo being referred

Blockers:
Instruction formats for PRU, discussing with the mentors

Week 10 target:
Complete chp 2.4 and chp2.5 of the Cpu0 reference repo

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Week 10
Tasks done in Week 10:

  • Working on the DagtoDagfiles, AsmInfo, Instruction Format files
  • Completed chp2.4 and chp2.5 of the Cpu0 repo being referred

Blockers:
Compilation issues while building

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Unfortunately a lot of valuable information was lost when TI shutdown their Wiki. But I managed to backup the information about PRU instruction format. See processors.wiki.ti.com Programmable_Realtime_Unit · dinuxbg/gnupru Wiki · GitHub

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This is really helpful, thank you so much! @dinux