Chapter 1: Introduction

Co-authored-by: Cliff Click <cliffc@acm.org>
Co-authored-by: Thalia Archibald <thalia@archibald.dev>
Co-authored-by: hadha <helsgithub15@gmail.com>
Co-authored-by: XmiliaH <45106915+XmiliaH@users.noreply.github.com>
Co-authored-by: Tamás Hadházy <85063808+Hels15@users.noreply.github.com>

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+# Simple
+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 show casing 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, RISC5 and ARM64 at least 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 levering Java: the Evaluator (first appears in Chapter
+10) directly slowly interprets the SoN IR.  Code-gen 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: Simple binary arithmetic such as addition, subtraction, multiplication, division
+  with constants. Peephole optimization / simple constant folding.
+* Chapter 3: 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 Struct types. Memory effects:
+  general memory edges in SSA.  Equivalence class aliasing.  Null pointer
+  analysis.  Peephole optimization around load-after-store/store-after-store.
+* Chapter 11: Global Code Motion - Scheduling.
+* Chapter 12: Float type.
+* Chapter 13: Nested references in Structs.
+* Chapter 14: Narrow primitive types (e.g. bytes)
+* Chapter 15: One dimensional static length array type, with array loads and stores.
+* Chapter 16: Constructors
+* Chapter 17: Mutability & 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 24: Chained conditionals and SCCP
+* Chapter 25: Modules and Separate Compilation