LLVM Techniques, Tips, and Best Practices: Clang and Middle-End Libraries

370 Pages·2021·18.442 MB·English

by  Min-Yih Hsu

LLVM Techniques,
Tips, and Best
Practices Clang and
Middle-End Libraries
Design powerful and reliable compilers using
the latest libraries and tools from LLVM
Min-Yih Hsu
BIRMINGHAM—MUMBAI
LLVM Techniques, Tips, and Best Practices
Clang and Middle-End Libraries
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To my parents.
– Min-Yih Hsu
Contributors
About the author
Min-Yih "Min" Hsu is a Ph.D. candidate in computer science at the University of
California, Irvine. His research focuses on compiler engineering, code optimization,
advanced hardware architectures, and system security. He has been an active member of
the LLVM community since 2015 and has contributed numerous patches upstream. Min
also dedicates his time to advocating LLVM and compiler engineering through various
avenues, such as writing blog posts and giving talks at conferences. In his spare time, Min
likes to explore a variety of different coffee beans and ways of brewing.
I want to thank the people who have supported me, especially my family
and my academic advisors. I also want to thank the LLVM community
for always being inclusive and kind to every member regardless of their
background and origin.
About the reviewer
Suyog Sarda completed his B.Tech from the College of Engineering, Pune. His work so far
has mostly been related to compilers. He is especially interested in the performance aspect
of compilers. He has worked on domain-specific language for image processing for DSPs.
LLVM's modularity makes it interesting to learn and implement quickly according to the
compiler's requirement. However, the documentation of LLVM is scattered. He hopes this
book provides a consolidated overview of the LLVM compiler infrastructure.

Table of Contents
Preface
Section 1:
Build System and LLVM-Specific Tooling
1
Saving Resources When Building LLVM
Technical requirements   4 Building as shared libraries   9
Cutting down building Splitting the debug info   9
resources with Building an optimized version of llvm-
better tooling   5 tblgen   10
Using the new PassManager and Clang   10
Replacing GNU Make with Ninja   5
Avoiding the use of the BFD linker   6 Using GN for a faster
turnaround time   11
Tweaking CMake arguments   7
Summary   13
Choosing the right build type   7
Further reading   14
Avoiding building all targets   8
2
Exploring LLVM's Build System Features
Technical requirements   16 Using the CMake function to add Pass
plugins   20
Exploring a glossary of LLVM's
important CMake directives   16
Understanding CMake
Using the CMake function to add new integration for
libraries   16 out-of-tree projects   21
Using the CMake function to add
Summary   24
executables and tools   20
ii Table of Contents
3
Testing with LLVM LIT
Technical requirements   26 Writing FileCheck directives   36
Using LIT in out-of-tree projects   26
Exploring the TestSuite
Preparing for our example project    27 framework   42
Writing LIT configurations   29
Preparing for our example project   42
LIT internals   32
Importing code into llvm-test-suite   43
Learning useful FileCheck tricks   34
Summary   46
Preparing for our example project   34
Further reading   46
4
TableGen Development
Technical requirements   48 Printing a recipe via the
Introduction to TableGen syntax   48 TableGen backend   60
Layout and records   50 TableGen's high-level workflow   62
Bang operators   51 Writing the TableGen backend   63
Multiclass   52 Integrating the RecipePrinter TableGen
backend   67
The DAG data type   53
Summary   70
Writing a donut recipe in
TableGen   55 Further reading   70
Section 2:
Frontend Development
5
Exploring Clang's Architecture
Technical requirements   74 LLVM, assemblers, and linkers   80
Learning Clang's subsystems
Exploring Clang's tooling
and their roles   75
features and extension options   81
Driver   76
Table of Contents iii
The FrontendAction class   81 Summary   85
Clang plugins   82 Further reading   85
LibTooling and Clang Tools   83
6
Extending the Preprocessor
Technical requirements   88 Developing custom
Working with SourceLocation preprocessor plugins and
and SourceManager   89 callbacks   99
Introducing SourceLocation   89 The project goal and preparation   100
Introducing SourceManager   90 Implementing a custom pragma
handler   103
Learning preprocessor and Implementing custom preprocessor
lexer essentials   91 callbacks   105
Understanding the role of the
Summary   108
preprocessor and lexer in Clang   92
Exercises   109
Understanding Token   93
Handling macros   97
7
Handling AST
Technical requirements   112 Project overview   125
Learning about AST in Clang   113 Printing diagnostic messages   128
Creating the AST plugin   132
In-memory structure of Clang AST   113
Types in Clang AST   116 Summary   144
ASTMatcher   118
Writing AST plugins   125
8
Working with Compiler Flags and Toolchains
Technical requirements   146 Project overview   150
Understanding drivers and Declaring custom driver flags   152
toolchains in Clang   147 Translating custom driver flags   155
Passing flags to the frontend   161
Adding custom driver flags   150