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JIT_COMPILER_STATUS.md
# JIT Compiler Implementation Status
## Overview
A Just-In-Time (JIT) compiler has been implemented for Octave to compile hot functions to native machine code for improved performance. The implementation uses LLVM as the code generation backend.
## Implementation Date
2026-01-23
## Current Status: **PHASE 1 COMPLETE**
The core JIT compiler infrastructure is complete and ready for incremental feature expansion.
---
## Completed Components
### 1. Core Infrastructure ✅
**Files:**
- `libinterp/jit/jit-compiler.h/cc` - Main compiler interface
- `libinterp/jit/jit-runtime.h/cc` - Runtime support for JIT code
- `libinterp/jit/jit-codegen.h` - Abstract code generation interface
**Features:**
- Compilation cache with function tracking
- Statistics collection (compilation count, execution count, timing)
- Enable/disable JIT compilation
- Function compilation management
### 2. LLVM Code Generation Backend ✅
**Files:**
- `libinterp/jit/jit-llvm-codegen.h/cc` - LLVM-based code generation
**Features:**
- LLVM IR generation from parse tree (basic structure)
- IR optimization passes (instruction combining, reassociation, GVN, CFG simplification)
- Native code generation using LLVM MCJIT
- ExecutionEngine management and cleanup
- Function pointer extraction
**Current IR Generation:**
- Traverses `tree_statement_list` from function body
- Creates LLVM function signatures
- Generates basic block structure
- Placeholder for expression and command code generation
### 3. Hot Function Detection ✅
**Files:**
- Extended `libinterp/parse-tree/profiler.h/cc`
**Features:**
- Configurable thresholds:
- Minimum call count (default: 1000)
- Minimum total execution time (default: 1.0 seconds)
- Minimum average time per call (default: 0.001 seconds)
- Function statistics tracking
- Integration with JIT compiler for automatic hot function identification
### 4. Interpreter Integration ✅
**Files:**
- `libinterp/corefcn/interpreter.h/cc` - Added JIT compiler member
- `libinterp/parse-tree/pt-eval.cc` - Integration in `execute_user_function()`
**Features:**
- JIT compiler accessible via `interpreter::get_jit_compiler()`
- Automatic check for JIT-compiled versions before interpreter execution
- Graceful fallback to interpreter if JIT execution fails
- Conditional compilation with `OCTAVE_ENABLE_JIT`
### 5. Build System Integration ✅
**Files:**
- `configure.ac` - Added `--enable-jit` option and LLVM detection
- `libinterp/jit/module.mk` - Build configuration for JIT module
- `libinterp/module.mk` - Integration into libinterp build
**Features:**
- `--enable-jit` configure option
- Automatic LLVM library detection
- Conditional compilation based on LLVM availability
- Proper linking with LLVM libraries
### 6. Execution Interface ✅
**Files:**
- `libinterp/jit/jit-compiler.cc` - `execute_compiled()` method
**Features:**
- Function pointer casting and invocation
- Argument passing structure (currently passes `octave_value_list` pointer)
- Return value handling structure
- Exception handling with fallback to interpreter
- Statistics tracking
---
## Architecture
```
┌─────────────────┐
│ Octave Code │
└────────┬────────┘
│
▼
┌─────────────────┐
│ Parser │
└────────┬────────┘
│
▼
┌─────────────────┐
│ Parse Tree │
└────────┬────────┘
│
├──────────────────┐
│ │
▼ ▼
┌─────────────────┐ ┌─────────────────┐
│ Interpreter │ │ JIT Compiler │
│ (tree_eval) │ │ │
└─────────────────┘ └────────┬────────┘
│
▼
┌─────────────────┐
│ Hot Function │
│ Detection │
└────────┬────────┘
│
▼
┌─────────────────┐
│ LLVM Codegen │
│ (IR Gen) │
└────────┬────────┘
│
▼
┌─────────────────┐
│ LLVM IR │
│ Optimization │
└────────┬────────┘
│
▼
┌─────────────────┐
│ Native Code │
│ (MCJIT) │
└────────┬────────┘
│
▼
┌─────────────────┐
│ Execution │
└─────────────────┘
```
---
## Usage
### Building with JIT Support
```bash
./configure --enable-jit
make
```
**Requirements:**
- LLVM development libraries installed
- LLVM headers available
### Enabling JIT at Runtime
The JIT compiler is disabled by default. To enable:
```octave
% Enable JIT compiler
jit_compiler = __get_jit_compiler__();
jit_compiler.set_enabled(true);
% Enable profiler (required for hot function detection)
profile on;
% Run your code - hot functions will be automatically compiled
% ... your code ...
```
---
## Future Work (Incremental Expansion)
### Phase 2: Expression IR Generation
**Priority: High**
1. **Arithmetic Operations**
- `tree_binary_expression` (+, -, *, /, etc.)
- `tree_unary_expression` (unary -, +, etc.)
- Type promotion and conversion
2. **Variable Access**
- `tree_identifier` - variable lookup and access
- Symbol table integration
- Scoping rules
3. **Assignments**
- `tree_assignment_expression`
- Variable storage
- Multiple assignment support
### Phase 3: Control Flow
**Priority: Medium**
1. **Conditional Statements**
- `tree_if_command` - if/else/elseif
- Boolean expression evaluation
- Branch optimization
2. **Loops**
- `tree_for_command` - for loops
- `tree_while_command` - while loops
- Loop optimization (unrolling, vectorization)
### Phase 4: Advanced Features
**Priority: Low**
1. **Function Calls**
- Built-in function calls
- User function calls
- Recursion support
2. **Array Operations**
- `tree_index_expression` - array indexing
- Matrix operations
- Sparse matrix support
3. **Type System**
- Dynamic type handling
- Type inference
- Type specialization
### Phase 5: Optimization
**Priority: Medium**
1. **Adaptive Compilation**
- Runtime performance metrics
- Recompilation with different optimization levels
- Profile-guided optimization
2. **Time-based Optimization**
- Execution time profiling integration
- Optimization targeting based on time spent
- Hot path identification
---
## Known Limitations
1. **IR Generation**: Currently only creates function structure. Actual expression/command code generation is pending.
2. **Type System**: Uses generic `void*` pointers for arguments/returns. Full Octave type system integration needed.
3. **LLVM Version**: Uses legacy LLVM APIs (MCJIT, legacy pass manager). May need updates for newer LLVM versions.
4. **Execution**: Currently falls back to interpreter. Full execution requires complete IR generation.
5. **Error Handling**: Basic exception handling. Full error propagation from JIT code needed.
---
## Testing
### Manual Testing
1. Enable JIT and profiler
2. Run code with hot functions
3. Check compilation statistics
4. Verify fallback to interpreter works
### Future Test Suite
- Unit tests for IR generation
- Integration tests for compilation pipeline
- Performance benchmarks
- Regression tests
---
## Configuration
### Hot Function Thresholds
Default thresholds can be adjusted:
```octave
prof = __get_profiler__();
prof.set_hot_thresholds(min_calls, min_total_time, min_avg_time);
```
### JIT Statistics
Access compilation statistics:
```octave
jit = __get_jit_compiler__();
stats = jit.get_statistics();
% Returns: compiled_count, execution_count, total_compilation_time, avg_compilation_time
```
---
## Files Modified/Created
### New Files
- `libinterp/jit/jit-compiler.h`
- `libinterp/jit/jit-compiler.cc`
- `libinterp/jit/jit-runtime.h`
- `libinterp/jit/jit-runtime.cc`
- `libinterp/jit/jit-codegen.h`
- `libinterp/jit/jit-llvm-codegen.h`
- `libinterp/jit/jit-llvm-codegen.cc`
- `libinterp/jit/module.mk`
### Modified Files
- `libinterp/corefcn/interpreter.h/cc` - Added JIT compiler member
- `libinterp/parse-tree/pt-eval.cc` - Integration point
- `libinterp/parse-tree/profiler.h/cc` - Hot function detection
- `libinterp/module.mk` - JIT module integration
- `configure.ac` - JIT and LLVM configuration
---
## Conclusion
The JIT compiler foundation is complete and ready for incremental feature expansion. The architecture supports:
- ✅ Hot function detection
- ✅ Compilation pipeline (IR generation → optimization → native code)
- ✅ Execution interface
- ✅ Integration with interpreter
- ✅ Build system support
The next phase should focus on implementing IR generation for simple expressions and arithmetic operations, which will enable basic JIT compilation for simple functions.
---
## References
- LLVM Documentation: https://llvm.org/docs/
- Octave Parse Tree: `libinterp/parse-tree/`
- Octave Interpreter: `libinterp/parse-tree/pt-eval.cc`