Douglas Chen presented on his contributions to LLVM. He discussed his motivation with CppNameLint and Clang-Tidy projects. He covered the workflows for Phabricator code reviews, building and testing code, and provided tips for contributors. He shared moments from his experience like design changes, invalid options, and how clang-tidy and tests work. He emphasized reading documentation and discussing with reviewers when facing issues.

1. Douglas Chen [陳鍵源] <dougpuob@gmail.com>
A trip about
how I contribute to LLVM
COSCUP 2021 Taiwan
2021/July/31

2. 2
1. Motivation
CppNameLint and Clang-Tidy
2. Beginning of a trip
Phabricator, Arcanist, Build, Test, and their
flows
3. Tips in a trip
Get out of trouble
4. Trip moments
Happened during the code review
5. The last
Agenda

3. Agenda
1. Motivation

4. 4
CppNameLint
Windows
Linux
macOS
https://github.com/dougpuob/cppnamelint
1. UpperCamel,
2. lowerCamel,
3. UPPER_SNAKE_CASE,
4. lower_snake_case,
5. szHungarianNotion

5. 5
Implement into Clang-Tidy
Clang-Tidy
CppNameLint
readability-identifier-naming
1. Libtooling (Clang based library)
2. Plenty checks (abseil-*, boost-*, cert-*, google-*, llvm-*, modernize-*,
performance-*, readability-, …)
3. Auto fix

6. Agenda
2. Beginning of a trip

7. 7
1. Phabricator (phab)
2. Arcanist (arc)
3. Build
4. Test

8. 8
Phabricator https://reviews.llvm.org/
arc
web-based
system
cmd utility
(Arcanist)

9. 9
Phabricator
LLVM Discussion Forums
(https://llvm.discourse.group/)
All recent commits
Chat Invite Link
(https://discord.gg/xS7Z362)
GitHub Repository
(https://github.com/llvm/llvm-project)
BuildBots
(https://lab.llvm.org/buildbot)
Review works you participate to

10. 10
Phabricator (differential page)
1⃣
3⃣
2⃣
4⃣
5⃣

11. 11
Phabricator flow (a life of a differential)
Create a
differential
and upload
to Phab
Make
a change
Discuss it
Request
changes
Ready
to land
Land it Close
LGTM
1⃣ 3⃣
2⃣
4⃣
5⃣
7⃣ 8⃣ 9⃣
6⃣
Approved

12. 12
Arcanist (command line interface for Phabricator)
● arc patch (apply changes in a revision to the working copy)
● arc lint (check your code for syntax and style errors)
● arc diff (send your code to Differential for review)
● arc land (push Git and Mercurial changes)
● arc help (shows this help)
● ...
arc

13. Local Git repo
13
Arcanist flow
Remote
Git repo
Central repo
with Phab
Code review
on Phab
arc land
arc diff
arc patch
git add
git commit
arc lint
Unaccepted
arc
Accepted
Ready to land
1⃣
3⃣
2⃣
4⃣
5⃣
7⃣
LGTM
6⃣

14. 14
Build (command with BuildKite)
cmake ../llvm
-G Ninja
-D LLVM_ENABLE_PROJECTS="clang;clang-tools-extra;libc;llvm"
-D CMAKE_BUILD_TYPE=Release
-D LLVM_ENABLE_ASSERTIONS=ON
-D LLVM_BUILD_EXAMPLES=ON
-D LLVM_LIT_ARGS="-v --xunit-xml-output test-results.xml"
-D LLVM_ENABLE_LLD=ON
-D CMAKE_CXX_FLAGS=-gmlt
https://buildkite.com/llvm-project/premerge-checks/builds/39326#578995ee-9588-4901-89eb-8deedf3caea0

15. 15
Test
1. Unit Test (in llvm/unittests with Google Test)
2. Regression Test (in llvm/test with llvm-lit - LLVM Integrated Tester)
3. Whole programs (test-suite, https://github.com/llvm/llvm-test-suite.git)
● ninja check-clang
● ninja check-llvm
● ninja check-all
Three
categories
Run via
build system

16. 16
Test (manual trigger unit test)
$ build-rel/tools/clang/tools/extra/unittests/clang-tidy/ClangTidyTests
Run it
Result

17. 17
Test (manual trigger regression test)
$ llvm-lit readability-identifier-naming-hungarian-notation.cpp
Result
Run it

18. 18
Test (buildbots & buildkite)
https://buildkite.com/llvm-project/premerge-checks/builds/39
326#578995ee-9588-4901-89eb-8deedf3caea0
https://lab.llvm.org/buildbot/#/waterfall

19. Agenda
3. Tips in the trip

20. # Based on main branch to create diff then send it for review
arc diff main --update D86671
# Based on the 99304d commit to create diff then send it for review
arc diff 99304d --update D86671
# Based on the 99304d commit to create diff but don’t send it out
arc diff 99304d --preview D86671
20
TIPS #1 Choose the right base

21. 21
TIPS #2 Generate documents
-DLLVM_ENABLE_SPHINX=ON
● ninja docs-clang-html
● ninja docs-clang-tools-html
● ninja docs-llvm-html
● ninja docs-dsymutil-man
● ninja docs-clang-man
● ninja docs-clang-tools-man
● ninja docs-llvm-dwarfdump-man
● ninja docs-llvm-man
Sphinx is a tool that makes it easy to
create intelligent and beautiful
documentation, written by Georg Brandl
and licensed under the BSD license. It was
originally created for the Python
documentation, and it has excellent
facilities for the documentation of
software projects in a range of languages.
Of course, this site is also created from
reStructuredText sources using Sphinx!
CMake
option
Build via
build system

22. 22
TIPS #3 You need an more powerful computer
Unit is mins
https:/
/dougpuob.github.io/posts/20210530-build-speed-comparison-btw-lxc-qemu-and-baremetal-by-llvm/

23. 23
TIPS #4 Linker is a memory monster
Add -DLLVM_USE_LINKER=lld
debug build
CMake option

24. Agenda
4. Trip moments

25. 25
Moment #1
int iVal = 0;
size_t nVal = 0;
uint8_t u8Val = 0;
uint16_t u16Val = 0;
uint32_t u32Val = 0;
BOOL bEnabled = TRUE;
ULONG ulVal = 0;
WORD wVal = 0;
DWORD dwVal = 0;
int *piVal = NULL;
char *szStr = “Str”;
char szText[] = “Text”;
Is there a standard for Hungarain notation ?
int iVal = 0;
int nVal = 0;
BOOL* bEnabled = TRUE;
BYTE* bValue = 0xA5;
char* szText = “Text”;
char* strText = “Text”;
Built-in
types
Microsoft
defined
Composite
types
❓
❓
❓

26. 26
Moment #2 Original idea was changed, but better

27. 27
Moment #3 Invalid identifier naming option
$ clang-tidy ./main.cpp
...
1 warning generated.
warning: invalid identifier naming option 'MacroDefinitionHungarianPrefix' [clang-tidy-config]
Checks: '-*,readability-identifier-naming'
CheckOptions:
- { key: readability-identifier-naming.MacroDefinitionHungarianPrefix, value: On }
- { key: readability-identifier-naming.AbstractClassHungarianPrefix , value: On }
- { key: readability-identifier-naming.ClassHungarianPrefix , value: On }
.clang-tidy
console output

28. 28
Moment #4
[Hungarian.WordList]
"uint32_t" = "u32"
"int" = "i"
"unsigned int" = "ui"
"DWORD" = "dw"
"BOOL" = "b"
limited configuration
readability-identifier-naming.HungarianNotation.PrimitiveType.uint32_t , value: u32
readability-identifier-naming.HungarianNotation.PrimitiveType.int , value: i
readability-identifier-naming.HungarianNotation.PrimitiveType.unsigned-int , value: i
readability-identifier-naming.HungarianNotation.PrimitiveType.DWORD , value: dw
readability-identifier-naming.HungarianNotation.PrimitiveType.BOOL , value: b
cppnamelint.toml
.clang-tidy

29. 29
Moment #5 How ‘--fix’ works
// readability-identifier-naming-hungarian-notation-cfgfile.cpp
int LocalVariableCase = 0;
warning: invalid case style for local variable 'LocalVariableCase' [readability-identifier-naming]
int LocalVariableCase = 0;
^~~~~~~~~~~~~~~~~
iLocalVariableCase
input source file
console output
clang-tidy source

30. 30
Moment #6 How Regression Test works
FileCheck check result
matching pattern
input from stdin or argv
pattern
regression test source

31. Agenda
5. The last

32. 32
If you was stuck ...
1. Read related documents on https://llvm.org/docs/ .
2. Search similar projects on GitHub.
3. Official community forum (https://llvm.discourse.group/)
4. Discuss with your reviewers.

33. 33
Reference (hightly recommend)
● https://llvm.org/docs/CodeReview.html
● https://llvm.org/docs/CodingStandards.html
● https://llvm.org/docs/DeveloperPolicy.html
● https://llvm.org/docs/Phabricator.html
● How to Contribute to LLVM (Bieneman & K. Barton)

34. Agenda
END