# Phase 2 Complete: Integerized IR with Arena Allocation

## Status: ✅ COMPLETE

### Completed Tasks:

**Task 3.1-3.3: IRRef Integer IDs** ✅
- `IRRef` now uses integer IDs for TEMP, LABEL, VAR, FUNCTION
- `IRRef::Kind` enum with integer `id` field
- `toString()` for debugging only

**Task 3.4: Symbol Table** ✅
- `SymbolTable` class with sequential integer indexing (0,1,2...)
- `intern()`, `lookup()`, `getName()` methods
- Scope management with `enterScope()` / `exitScope()`

**Task 3.5: Arena Allocator** ✅
- `Arena` class with 64KB default block size
- `allocate()` and `create<T>()` methods
- `reset()` and `clear()` for memory management
- Block tracking with `numBlocks()` and `totalAllocated()`

**Task 3.7: Flat Array IR Storage** ✅
- `IRFunction::instructions` now `std::vector<IRInstruction>`
- Contiguous memory layout for cache efficiency
- No more `unique_ptr` or `shared_ptr` overhead

**Task 3.9: IR Generation with Integer References** ✅
- `IRGenerator` uses integer IDs throughout
- Symbol table integration for variable lookups
- No string-based temporary/label generation

**Task 3.10: Unit Tests** ✅
- `test_integerized_ir.cpp`: 10 tests covering all features
- `test_pratt_unit.cpp`: 6 tests for Pratt parser
- All tests passing

**Task 4: Checkpoint Verification** ✅
- Compiler builds successfully
- `hello-world.ac` compiles and runs correctly
- IR generation working with integer references
- No regressions

### Test Results:

```bash
# Pratt Parser Tests
✓ Binary operator precedence
✓ Unary operators  
✓ Function calls
✓ Array indexing
✓ Nested expressions
✓ Comparison operators

# Integerized IR Tests
✓ Integer temporary references
✓ Integer label references
✓ Symbol table integer indexing
✓ Symbol table nested scopes
✓ Arena allocator
✓ Arena typed allocation
✓ Flat array IR storage
✓ IRProgram integration
✓ Variable references use integer IDs
✓ String conversion for debugging only

# Integration Tests
✓ hello-world.ac → Python (compiles and runs)
✓ test_expressions.ac → Python (compiles and runs)
```

### Performance Improvements:

- **Memory**: Flat arrays reduce fragmentation, arena allocation eliminates per-instruction overhead
- **Cache**: Contiguous instruction storage improves cache locality
- **Speed**: Integer IDs eliminate string comparisons and hash lookups

### Next Phase:

**Phase 3: CFG Lowering (Tasks 5.1-5.6)**
- Add jump/label IR instructions
- Lower IF/WHILST/FOR to explicit control flow
- Eliminate high-level control structures from IR
