JIT_CURRENT_STATUS.md

# JIT Compiler - Current Status

## Date: 2026-01-23

## Overview

This document provides the current status of the JIT compiler implementation, including what has been completed and what remains to be done.

---

## ✅ Completed Features

### Core Infrastructure
- ✅ JIT compiler framework (`jit-compiler.h/cc`)
- ✅ LLVM backend integration (`jit-llvm-codegen.h/cc`)
- ✅ Runtime support (`jit-runtime.h/cc`)
- ✅ IR generator framework (`jit-ir-generator.h/cc`)
- ✅ Hot function detection using profiler
- ✅ Compilation cache management
- ✅ Integration with interpreter (`interpreter.h/cc`, `pt-eval.cc`)

### Basic Expressions (Phase 1)
- ✅ Constant values (numbers, strings)
- ✅ Variable identifiers (local, global, persistent)
- ✅ Binary expressions (arithmetic, comparison, logical)
- ✅ Unary expressions (negation, etc.)
- ✅ Simple assignments
- ✅ Power operator (via runtime call)

### Control Flow (Phase 2)
- ✅ If-else statements
- ✅ While loops
- ✅ For loops (simple)
- ✅ Do-until loops
- ✅ Break statements
- ✅ Continue statements
- ✅ Return statements (structure in place)
- ✅ Switch statements (basic implementation)

### Runtime Functions
- ✅ `call_function()` - Execute Octave functions
- ✅ `array_get_element()` - Array indexing
- ✅ `array_set_element()` - Array assignment
- ✅ `create_matrix()` - Matrix construction
- ✅ `create_range()` - Range creation for colon expressions
- ✅ `get_array_dims()` - Array dimensions
- ✅ Array arithmetic operations (add, sub, mul, div)
- ✅ Memory management (allocate, free)

---

## ⏳ Partially Implemented

### Return Value Handling
**Status:** Structure in place, needs completion

**Current State:**
- Function signature returns `void*` (pointer to `octave_value_list`)
- `execute_compiled()` receives pointer but doesn't convert it properly
- IR generator returns null pointer as placeholder

**What's Needed:**
- Track return values throughout function execution
- Allocate `octave_value_list` in IR
- Convert LLVM values to `octave_value`
- Return pointer to allocated list
- Convert pointer back to `octave_value_list` in `execute_compiled()`

**Complexity:** Medium - requires runtime memory management

---

## ❌ Not Yet Implemented

### Function Call IR Generation
**Status:** Detected but not implemented

**Location:** `jit-ir-generator.cc:generate_index_expr_ir()`

**What's Needed:**
- Generate IR to build `octave_value_list` from arguments
- Generate IR to call runtime `call_function()` from LLVM
- Handle return values from function calls
- Support for user functions, built-ins, and MEX functions

**Blocking Issue:** LLVM IR cannot directly call C++ member functions. Requires C-style wrappers.

**Complexity:** High - requires architectural change (C-style wrappers)

---

### Matrix Construction IR Generation
**Status:** Returns null, falls back to interpreter

**Location:** `jit-ir-generator.cc:generate_matrix_ir()`

**What's Needed:**
- Evaluate all matrix elements
- Determine matrix dimensions
- Generate IR to call `runtime.create_matrix()`
- Handle variable-sized matrices

**Blocking Issue:** Requires runtime call IR generation infrastructure

**Complexity:** Medium-High - depends on runtime call IR generation

---

### Colon Expression Range Creation
**Status:** Returns base value, falls back to interpreter

**Location:** `jit-ir-generator.cc:generate_colon_expr_ir()`

**What's Needed:**
- Generate IR to create range objects via `runtime.create_range()`
- Handle infinity cases
- Support range iteration in for loops

**Blocking Issue:** Requires runtime call IR generation infrastructure

**Complexity:** Medium - depends on runtime call IR generation

---

### Array Indexing IR Generation
**Status:** Returns base value, falls back to interpreter

**Location:** `jit-ir-generator.cc:generate_index_expr_ir()`

**What's Needed:**
- Generate IR to build index lists
- Generate IR to call `runtime.array_get_element()`
- Handle vector indices, colon indices, etc.
- Convert results back to LLVM values

**Blocking Issue:** Requires runtime call IR generation infrastructure

**Complexity:** Medium - depends on runtime call IR generation

---

### Cell Array Construction
**Status:** Not implemented

**Location:** `jit-ir-generator.cc:generate_cell_ir()`

**What's Needed:**
- Similar to matrix construction but with heterogeneous types
- Runtime support for cell arrays

**Complexity:** Medium - depends on runtime call IR generation

---

### Advanced Features
- ❌ Increment/decrement with side effects
- ❌ Indexed assignment (`a(i) = value`)
- ❌ Complex for command (multiple loop variables)
- ❌ Try-catch exception handling
- ❌ Multi-assignment statements
- ❌ Function handles
- ❌ Anonymous functions
- ❌ Class definitions

---

## 🔧 Architectural Requirements

### C-Style Runtime Wrappers

The main blocker for many features is that **LLVM IR cannot directly call C++ member functions**. To enable runtime calls from JIT-compiled code, we need:

1. **C-Style Wrapper Functions:**
   ```c
   extern "C" {
     void* jit_runtime_call_function(void* runtime_ptr, const char* name, void* args, int nargout);
     void* jit_runtime_create_matrix(void* runtime_ptr, void* elements, int rows, int cols);
     void* jit_runtime_create_range(void* runtime_ptr, double base, double limit, double increment);
     // ... etc
   }
   ```

2. **Runtime Pointer Storage:**
   - Store pointer to `jit_runtime` instance in IR generator
   - Pass as first parameter to all wrapper functions

3. **Type Conversion:**
   - Convert LLVM values to C types
   - Convert C return values back to LLVM values
   - Handle `octave_value` and `octave_value_list` conversions

4. **Memory Management:**
   - Allocate/deallocate `octave_value_list` objects
   - Track memory for cleanup

**Estimated Effort:** 2-3 days of focused work

---

## 📊 Implementation Statistics

- **Total Lines of Code:** ~3000+ lines in `libinterp/jit/`
- **Files:** 8 core files (headers + implementations)
- **Completion:** ~60% of core features
- **Runtime Functions:** 10/10 implemented
- **IR Generation:** ~40% complete

---

## 🎯 Next Steps (Priority Order)

1. **High Priority:**
   - Implement C-style runtime wrappers
   - Complete return value handling
   - Implement function call IR generation

2. **Medium Priority:**
   - Matrix construction IR generation
   - Colon expression range creation
   - Array indexing IR generation

3. **Low Priority:**
   - Cell array construction
   - Advanced features (try-catch, function handles, etc.)
   - Performance optimizations

---

## 📝 Notes

- The JIT compiler currently works for simple expressions and control flow
- Complex operations (function calls, matrix construction) fall back to interpreter
- This is a reasonable approach for incremental development
- Full implementation requires the C-style wrapper infrastructure

---

## 🔗 Related Documents

- `JIT_IMPLEMENTATION_COMPLETE.md` - Initial implementation summary
- `JIT_REMAINING_WORK_COMPLETE.md` - Previous work completion summary
- `JIT_IR_GENERATION_PLAN.md` - Detailed IR generation plan
- `jit-test-issues.md` - Testing issues and recommendations