justjit 0.1.4

Fast Python JIT compiler using LLVM ORC - lowers Python bytecode to native machine code

JustJIT

A high-performance Just-In-Time compiler for Python that leverages LLVM's ORC JIT infrastructure to compile Python bytecode to native machine code at runtime.

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Table of Contents

• Overview
• Features
• Installation
• Quick Start
• Architecture
• Supported Python Features
• Generator and Coroutine Support
• Control Flow Graph (CFG) Implementation
• Exception Handling
• Current Limitations
• Building from Source
• API Reference
• Contributing
• License

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Overview

JustJIT transforms Python functions into optimized native machine code using LLVM. Unlike traditional interpreters that execute bytecode instruction-by-instruction, JustJIT analyzes Python bytecode and generates equivalent LLVM IR, which is then optimized and compiled to native code.

How It Works

1. Bytecode Extraction: Parse Python function bytecode using the dis module
2. IR Generation: Translate each opcode to LLVM IR, maintaining Python semantics
3. Optimization: Apply LLVM optimization passes (O0-O3)
4. Compilation: JIT compile to native machine code
5. Execution: Call the native function with Python object arguments

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Features

Core Features

• Python 3.10+ Bytecode Support: Full support for Python 3.10-3.13 bytecode formats
• LLVM ORC JIT v2: Modern JIT infrastructure with lazy compilation support
• Multiple Compilation Modes:
  • object mode: Full Python object semantics
  • int mode: Pure integer arithmetic (10x faster for numeric code)
  • auto mode: Automatic detection based on function analysis

Advanced Features

• Generator Support: Full state machine implementation for yield
• Coroutine Support: Async/await with proper awaitable protocol
• Exception Handling: Python 3.11+ exception table parsing
• Pattern Matching: match/case statements with CFG analysis
• Closure Support: Captured variables from enclosing scopes
• Comprehensions: List, dict, and set comprehensions

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Installation

From PyPI (Recommended)

pip install justjit

From Source

See Building from Source for detailed instructions.

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Quick Start

Basic Usage

from justjit import jit

@jit
def fibonacci(n):
    if n <= 1:
        return n
    a, b = 0, 1
    for _ in range(n - 1):
        a, b = b, a + b
    return b

result = fibonacci(40)  # Runs as native code

Generator Functions

from justjit import jit

@jit
def count_up(n):
    i = 0
    while i < n:
        yield i
        i += 1

for value in count_up(10):
    print(value)

Async Functions

from justjit import jit
import asyncio

@jit
async def fetch_data():
    await asyncio.sleep(0.1)
    return "data"

result = asyncio.run(fetch_data())

Integer Mode (Maximum Performance)

from justjit import jit

@jit(mode='int')
def sum_range(n):
    total = 0
    for i in range(n):
        total += i
    return total

# Pure LLVM i64 arithmetic - no Python object overhead
result = sum_range(1000000)

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Architecture

Project Structure

justjit/
├── src/
│   ├── jit_core.cpp       # Core JIT engine (~12,000 lines)
│   │                      # - Opcode handlers for all Python bytecode
│   │                      # - Generator state machine compiler
│   │                      # - Coroutine compiler with await handling
│   │                      # - CFG analysis and PHI node generation
│   │                      # - Exception table parsing and handling
│   ├── jit_core.h         # JIT engine header
│   │                      # - JITGeneratorObject and JITCoroutineObject types
│   │                      # - BasicBlockInfo and CFGStackState for CFG
│   │                      # - Python C API function declarations
│   ├── bindings.cpp       # nanobind Python bindings
│   ├── opcodes.h          # Python 3.13 opcode definitions
│   └── justjit/
│       └── __init__.py    # Python interface (~800 lines)
│                          # - @jit decorator
│                          # - Bytecode extraction
│                          # - Exception table parsing
│                          # - Fallback handling
├── docs/
│   ├── OPCODES_REFERENCE.md      # Detailed opcode documentation
│   └── ASYNC_IMPLEMENTATION_RESEARCH.md
├── CMakeLists.txt         # Build configuration
├── pyproject.toml         # Python package metadata
├── OPCODE_STATUS.md       # Implementation status tracker
└── CFG_IMPLEMENTATION_PLAN.md    # CFG architecture design

Core Components

Component	Description
JITCore	Main compiler class managing LLVM context, module, and JIT engine
compile_function	Compiles regular Python functions to native code
compile_generator	Transforms generators into state machine step functions
compile_coroutine	Handles async functions with await/send protocol
CFG Analysis	Control flow graph with PHI nodes for SSA form

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Supported Python Features

Fully Implemented (95+ opcodes)

Control Flow

• if/elif/else statements
• for loops with range(), lists, tuples
• while loops
• break/continue
• return statements

Data Types

• Integers, floats, strings, booleans, None
• Lists, tuples, dicts, sets
• Slicing (x[1:3], x[::2])
• Comprehensions (list, dict, set)

Operations

• All arithmetic: +, -, *, /, //, %, **, @
• All bitwise: &, |, ^, ~, <<, >>
• All comparison: <, <=, >, >=, ==, !=
• Membership: in, not in
• Identity: is, is not
• Boolean: and, or, not
• Augmented assignment: +=, -=, *=, etc.

Functions

• Function calls with positional and keyword arguments
• *args and **kwargs
• Default arguments
• Closures and nested functions
• Lambda expressions (via nested function)

Classes

• Attribute access (obj.attr)
• Method calls
• super() calls
• __build_class__ for class creation

Exception Handling

• try/except/finally
• raise with optional cause
• Exception type matching
• Stack unwinding with proper cleanup

Pattern Matching (Python 3.10+)

• match/case statements
• Sequence patterns: case [a, b, c]
• Mapping patterns: case {"key": value}
• Class patterns: case Point(x, y)
• Wildcard: case _
• Guards: case x if x > 0

Imports

• import module
• from module import name
• from module import *

String Formatting

• f-strings: f"Hello, {name}!"
• Format specs: f"{value:.2f}"
• Conversions: !r, !s, !a

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Generator and Coroutine Support

Generator Implementation

JustJIT compiles generators into state machine step functions. Each yield creates a suspension point with a unique state ID.

// Generator step function signature
PyObject* step_func(int32_t* state, PyObject** locals, PyObject* sent_value);

// State values:
//   0 = initial (not started)
//   1..N = resume points after each yield
//   -1 = completed (returned)
//   -2 = error occurred

Generator Object Structure

struct JITGeneratorObject {
    PyObject_HEAD
    int32_t state;              // Current suspension state
    PyObject** locals;          // Persistent local variables
    Py_ssize_t num_locals;      // Including stack spill slots
    GeneratorStepFunc step_func; // Compiled native function
    PyObject* name;             // For __name__
    PyObject* qualname;         // For __qualname__
};

How Generator Compilation Works

1. State Identification: Each YIELD_VALUE opcode gets a unique state ID
2. State Dispatch: Entry creates a switch on *state to jump to correct resume point
3. Stack Persistence: Values are spilled to persistent slots before yield
4. Resume Restoration: Stack values are restored from slots after resume

Coroutine Implementation

Coroutines extend generators with the awaitable protocol:

struct JITCoroutineObject {
    PyObject_HEAD
    int32_t state;              // Suspension state
    PyObject** locals;          // Persistent locals
    Py_ssize_t num_locals;
    GeneratorStepFunc step_func;
    PyObject* name;
    PyObject* qualname;
    PyObject* awaiting;         // Currently awaited object
};

Await Handling

The SEND opcode handles await delegation:

1. GET_AWAITABLE: Get iterator from awaited object
2. SEND None: Start iteration
3. SEND value: Forward sent values to sub-iterator
4. END_SEND: Handle completion, extract return value

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Control Flow Graph (CFG) Implementation

JustJIT implements proper SSA (Static Single Assignment) form using CFG analysis and PHI nodes for complex control flow patterns.

Why CFG is Needed

Python bytecode simulates a value stack. When control flow merges (e.g., after if/else), different paths may have pushed different values. LLVM requires each value to have a single definition point, so we use PHI nodes to merge values from different paths.

CFG Data Structures

struct BasicBlockInfo {
    int start_offset;                  // Block start
    int end_offset;                    // Block end
    std::vector<int> predecessors;     // Incoming edges
    std::vector<int> successors;       // Outgoing edges
    int stack_depth_at_entry;          // Expected stack depth
    bool is_exception_handler;         // Handler block flag
    bool needs_phi_nodes;              // Multiple predecessors
    llvm::BasicBlock* llvm_block;      // LLVM representation
};

PHI Node Generation

When compiling pattern matching (match/case):

1. Block Analysis: Identify all case blocks and their targets
2. Stack Tracking: Track stack state at each merge point
3. PHI Creation: At merge blocks, create PHI nodes for each stack slot
4. Value Wiring: Connect incoming values from each predecessor

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Exception Handling

JustJIT parses Python 3.11+ exception tables to handle try/except blocks correctly.

Exception Table Format

# Exception table entry structure
{
    "start": 10,    # Protected range start (byte offset)
    "end": 50,      # Protected range end
    "target": 100,  # Handler offset (PUSH_EXC_INFO)
    "depth": 2,     # Stack depth to unwind to
    "lasti": False  # Whether to push last instruction
}

Error Checking Pattern

Every Python C API call that can fail is wrapped with error checking:

// After each potentially-failing call
auto check_error_and_branch = [&](llvm::Value* result, ...) {
    // Check if result is NULL
    auto is_null = builder->CreateIsNull(result);
    
    // If NULL, unwind stack and jump to handler
    builder->CreateCondBr(is_null, error_block, continue_block);
};

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Current Limitations

Not Yet Implemented

Feature	Status	Notes
Async Generators	❌	async def with yield
async for	❌	Needs GET_AITER/GET_ANEXT
async with	⚠️	Basic support, not fully tested
Generator Comprehensions in Generators	❌	Complex stack handling across yields

Known Issues

1. Generator + List Comprehension: When a generator contains a list comprehension, the stack handling across YIELD_VALUE is incomplete. The list builds correctly, but stack spilling/restoration needs refinement.

2. Deeply Nested Async: Chains of await expressions with complex nesting may have edge cases.

Fallback Behavior

When JustJIT encounters unsupported opcodes or patterns, it automatically falls back to Python execution with a warning:

RuntimeWarning: Generator 'my_gen' uses opcodes not yet supported by JIT.
Using Python implementation (no performance impact for generators).

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Building from Source

Prerequisites

Requirement	Version
Python	3.10+
CMake	3.20+
LLVM	18.1.8+
C++ Compiler	C++17 support
nanobind	2.0.0+

Windows Build

# Set LLVM path
$env:LLVM_DIR = "C:\path\to\llvm\build\lib\cmake\llvm"

# Build and install
pip install -e . --no-build-isolation

Linux Build

# Set LLVM path
export LLVM_DIR=/path/to/llvm/build/lib/cmake/llvm

# Build and install
pip install -e . --no-build-isolation

macOS Build

# With Homebrew LLVM
export LLVM_DIR=$(brew --prefix llvm)/lib/cmake/llvm

# Build and install  
pip install -e . --no-build-isolation

CMake Configuration

cmake -B build \
    -DLLVM_DIR=/path/to/llvm/lib/cmake/llvm \
    -DCMAKE_BUILD_TYPE=Release \
    -DPython_EXECUTABLE=$(which python)

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API Reference

@jit Decorator

@jit(
    opt_level=3,      # LLVM optimization level (0-3)
    vectorize=True,   # Enable loop vectorization
    inline=True,      # Enable function inlining
    parallel=False,   # Enable parallelization (experimental)
    lazy=False,       # Delay compilation until first call
    mode='auto'       # 'auto', 'object', or 'int'
)
def my_function(...):
    ...

dump_ir() Function

from justjit import dump_ir

@dump_ir
def my_func(x):
    return x + 1

# Prints the generated LLVM IR
my_func(5)

Direct API Access

from justjit import JIT

jit = JIT()
jit.set_opt_level(3)
success = jit.compile_function(
    instructions, constants, names,
    globals_dict, builtins_dict,
    closure_cells, exception_table,
    "my_func", param_count=2, total_locals=5, nlocals=5
)
if success:
    callable = jit.get_callable("my_func", param_count=2)
    result = callable(arg1, arg2)

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Contributing

Contributions are welcome! Please ensure:

1. Code Style: Follow existing patterns in the codebase
2. Testing: Test with various Python code patterns
3. Documentation: Update docs for new features
4. Compatibility: Maintain Python 3.10+ and cross-platform support

Development Workflow

# Clone the repository
git clone https://github.com/magi8101/justjit.git
cd justjit

# Create development environment
python -m venv venv
source venv/bin/activate  # or .\venv\Scripts\Activate.ps1 on Windows

# Install in development mode
pip install -e . --no-build-isolation

# Run tests
python -c "from justjit import jit; @jit\ndef f(x): return x*2\nprint(f(21))"

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License

MIT License - see LICENSE for details.

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Acknowledgments

Built with:

• LLVM Project - Compiler infrastructure
• Python - The language we're optimizing
• nanobind - C++/Python bindings

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Links

• Repository: github.com/magi8101/justjit
• Issues: github.com/magi8101/justjit/issues