path: root/README.md

# Simple
English | [日本語](README.ja.md)

A Simple showcase for the Sea-of-Nodes compiler IR

This repo is intended to demonstrate the Sea-of-Nodes compiler IR.

The Sea-of-Nodes is the core IR inside of HotSpot's C2 compiler
and Google's V8 compiler and Sun/Oracle's Graal compiler.

Since we are showcasing the SoN IR, the *language* being implemented is less
important.  We're using a very simple language similar to C or Java, but with
far fewer features.  Simple is strongly typed, object-oriented, with first-class
*functions* not *closures*.  Object references are pointers, and null
pointer exceptions are disallowed by the typing system.  Arrays will probably
be range-checked at some point, making Simple a fully safe language.  Simple
has a minimal syntax that can be parsed with a recursive descent parser.

The Sea-of-Nodes is used for machine code generation in these industrial
strength systems - but for this demonstration the backend is both difficult and
less important.  This repo targets x86-64, RISC-V and ARM64 with
ahead-of-time compilation - but with an eye towards JIT compilation.

This repo also is not intended to be a complete language in any sense, and so
the backend starts with a Java evaluator (first introduced in Chapter
8) that directly interprets the SoN IR. Code generation first appears in Chapter
19.


## Chapters

The following is a rough plan, subject to change.

Each chapter will be self-sufficient and complete; in the sense that each
chapter will fully implement a subset of the Simple language, and include
everything that was created in the previous chapter.  Each chapter will also
include a detailed commentary on relevant aspects of the Sea Of Nodes
intermediate representation.

The Simple language is styled after a subset of C or Java.

* [Chapter 1](docs/chapter01/README.md): Script that returns an integer literal, i.e., an empty function that takes no arguments and returns a single integer value. The `return` statement.
* [Chapter 2](docs/chapter02/README.md): Simple binary arithmetic such as addition, subtraction, multiplication, division
  with constants. Peephole optimization / simple constant folding.
* [Chapter 3](docs/chapter03/README.md): Local variables, and assignment statements. Read on RHS, SSA, more peephole optimization if local is a
  constant.
* Chapter 4: A non-constant external variable input
  named `arg`.  Binary and Comparison operators involving constants and `arg`.
  Non-zero values will be truthy.  Peephole optimizations involving algebraic
  simplifications.
* Chapter 5: `if` statement. CFG construction.
* Chapter 6: Peephole optimization around dead control flow.
* Chapter 7: `while` statement; looping constructs - eager phi approach.
* Chapter 8: Looping constructs continued, lazy phi creation, `break` and `continue` statements.
* Chapter 9: Global Value Numbering. Iterative peepholes to fixpoint. Worklists.
* Chapter 10: User defined structs, pointers and null
  analysis. One memory value in SSA. Loads, stores, and an executable evaluator.
* Chapter 11: Equivalence class aliasing. Lazy memory
  partitioning with `MemMerge`, `MemPhi`, and `BulkMemPhi`.
* Chapter 12: Reference fields, forward references and recursive structs.
* Chapter 13: Global Code Motion - Scheduling.
* Chapter 14: Numeric types: floats, narrow integers, ranges and rounding to `f32`.
* Chapter 15: One dimensional static length array type, with array loads and stores.
* Chapter 16: Constructors
* Chapter 17a: Binding mutability, reference permissions, and deep read-only views.
* Chapter 17b: Syntax sugar: `var`, `val`, `x+=y`, `for(init; test; next) body`
* Chapter 18: Functions and calls.
* Chapter 19: Instruction selection and portable compilation
* Chapter 20: Graph Coloring Register Allocation
* Chapter 21: Instruction Encodings & ELF
* Chapter 22: A Simple Hello, World!
* Chapter 23: Methods and Types Revisited
* Chapter 24a: SCCP Within a Function
* Chapter 24b: SCCP Across Functions
* Chapter 25: SSA Before Types Are Known
* Chapter 26: Construction and Private Memory
* Chapter 27: Escape Analysis and Unknown Callers
* Chapter 28a: Modules and Lazy Class Initialization
* Chapter 28b: Separate Compilation

Appendices: [Native libraries](docs/appendices/native-libraries.md),
[optimizer and backend tuning](docs/appendices/optimizer-tuning.md).
Future compiler and language work is collected in the [roadmap](docs/roadmap.md).

## Building across chapters

The optional [interactive graph viewer](graph/README.md) is shared in `graph/`.
All chapters launch it with `make view` from the chapter directory.

The [debug printers](print/README.md) are shared in `print/`; Chapter 2 needs only
a one-line expression format. A shared `BaseNode` supplies identity and edge
access to both printers and the viewer; chapter adapters add semantic details
as the IR grows.

The [instruction encoders](isa/README.md) share x86-64, ARM, and RISC-V byte
emission for Chapters 21–28b, along with ARM/RISC-V test evaluators. Machine-node
selection, register allocation, and code layout remain in each chapter; the
shared layer takes concrete operands and writes bytes.

The top-level Makefile runs each chapter's `tests`, `tags` (also `tag`),
`release`, or `lib` target. Start with `make lib` on a fresh checkout, then
`make tests`.

CI runs `make lib tests CTAGS=` on Linux with JDK 21. The Make targets also build
Chapter 28b's native runtime and `sys` library before running the tests that use
them; Maven's Java build alone does not produce those prerequisites.

Chapters 10-14 cover whole memory,
lazy alias splitting, references, GCM, and numeric types in that order.
Later chapters build on this memory representation.

To build and test just the memory chapters:

```sh
make lib tests release CHAPTERS="chapter10 chapter11 chapter12"
```

Every chapter has an IntelliJ module with its own compiler and test classpath.
See [the IntelliJ setup](docs/intellij.md) to open and debug any chapter's tests.
The root Maven reactor also includes every chapter.
Make and the linear-history workflow discover the numbered chapter directories.