# TODO - Performance & Differentiation Focus

## Performance Optimization Roadmap

### High Priority - Core Performance
- [x] Implement inline caching for invokevirtual/invokeinterface
- [x] Add method inlining for small hot methods
- [x] Implement escape analysis for stack allocation
- [x] Optimize instruction dispatch with computed goto or template JIT
- [x] Profile and optimize class loading (.jvmc cache format validation)
- [x] Benchmark GC pause times and implement concurrent marking

### Medium Priority - JIT Optimization
- [x] Expand Cranelift JIT coverage to 80%+ opcodes
- [x] Implement on-stack replacement (OSR) for long-running loops
- [x] Add profile-guided optimization (PGO) support
- [x] Implement register allocation improvements
- [x] Add loop unrolling and vectorization
- [x] Optimize AOT compilation with link-time optimization (LTO)

### Low Priority - Specialized Optimizations
- [x] Add specialized implementations for common patterns (String ops, Math functions)
- [x] Implement zero-copy array operations with SIMD
- [x] Add compressed oops for memory-constrained environments
- [x] Implement thread-local allocation buffers (TLAB)
- [x] Add biased locking for uncontended synchronization

---

## Competitive Differentiation Enhancements

### Unique JVMRS Features (vs HotSpot, OpenJ9, GraalVM)

#### Rust Ecosystem Integration
- [x] Direct Rust-Java interop without JNI overhead
- [x] Rust crate integration system for Java extensions
- [x] Compile-time Java-to-Rust binding generation (jvmrs-bindgen)
- [x] Rust macro system for Java class definitions (jvmrs-macros)
- [ ] IDE plugins for cross-language debugging
- [ ] Automated binding generation for existing Java libraries

#### Next-Generation Deployment Targets
- [x] WASI (WebAssembly System Interface) support
- [x] Browser-based Java execution via WASM
- [x] Edge computing optimizations
- [x] Serverless platform optimizations
- [ ] WASM GC integration for full Java semantics
- [ ] WASI async/await bridge for Java code

#### Specialized Use Cases
- [x] Blockchain/deterministic execution mode
- [x] Real-time systems with guaranteed pause times
- [x] High-frequency trading with ultra-low latency
- [ ] Safety-critical systems with formal verification
- [ ] Deterministic replay for production debugging
- [ ] Cryptographic verification of bytecode

#### Developer Experience Advantages
- [ ] IDE plugins for cross-language debugging
- [x] Hot reloading for Java/Rust hybrid development
- [x] Performance profiling with Rust tooling integration
- [x] Rust documentation system for Java APIs
- [x] Interactive REPL for JVM exploration
- [ ] Visual debugging for polyglot code

#### Embedded and IoT
- [x] no_std support for bare-metal targets
- [ ] ARM Cortex-M optimizations
- [ ] RISC-V backend support
- [ ] Sub-1MB footprint for constrained devices
- [ ] Real-time GC with bounded pause times

---

## Benchmarking & Validation

### Performance Benchmarks
- [ ] Comprehensive benchmark suite vs HotSpot/OpenJ9/GraalVM
- [ ] Startup time comparisons (cold start optimization)
- [ ] Memory footprint benchmarks (heap, perm gen, code cache)
- [ ] Throughput benchmarks (DaCapo, SPECjvm)
- [ ] GC pause time analysis and comparison
- [ ] JIT warmup curve analysis

### Differentiation Validation
- [ ] Security vulnerability comparison (CVE analysis)
- [ ] Memory safety demonstrations (fuzzing results)
- [ ] WASM execution performance vs browser JVM emulators
- [ ] Embedded target comparison (microcontroller benchmarks)
- [ ] Polyglot interop overhead vs JNI

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## Technical Debt & Infrastructure

### Code Quality
- [ ] Increase unit test coverage to 90%+
- [ ] Add property-based tests for critical components
- [ ] Implement continuous benchmarking in CI
- [ ] Add performance regression detection
- [ ] Improve error messages and diagnostics

### Documentation
- [ ] Complete inline API documentation
- [ ] Add performance tuning guide
- [ ] Write polyglot programming guide
- [ ] Document deployment scenarios (WASM, embedded, serverless)
- [ ] Create architecture diagrams for key components

---

## Research & Innovation

### Experimental Features
- [ ] Experimental GC algorithms (ZGC-like, Shenandoah-like)
- [ ] Alternative JIT backends (LLVM-based, RBJIT)
- [ ] Ahead-of-time native compilation (native-image alternative)
- [ ] Multi-tier memory management (NVMe, persistent memory)
- [ ] Hardware-accelerated cryptography integration

### Future Differentiators
- [ ] Machine learning-guided optimization
- [ ] Formal verification of bytecode execution
- [ ] Deterministic distributed execution
- [ ] Quantum computing integration (exploratory)
- [ ] Neuromorphic processor support (exploratory)

---

## Completed ✓

### Core Performance
- [x] Arena-based allocators for improved cache locality
- [x] Generational GC with parallel sweep using rayon
- [x] JIT compilation tiered strategy (interpreter → JIT)
- [x] Cranelift JIT for baseline compilation
- [x] Fast class loading with caching
- [x] Validated .jvmc cache format (checksum + mtime, v2 format with v1 backward compat)
- [x] Function-pointer dispatch table for hot opcodes (computed-goto style)
- [x] Expanded Cranelift JIT to 80+ opcodes (constants, loads/stores, arithmetic, branches, conversions, comparisons)
- [x] AOT compilation with LTO-style optimizations (opt_level, enable_alias_analysis, expanded opcode coverage)
- [x] JIT register allocation: local variable caching in Cranelift virtual registers (eliminates redundant frame FFI calls)
- [x] JIT loop unrolling: bytecode-level factor-2 unroll for small, branch-free loops ending in iinc+goto
- [x] Specialized native intrinsics: Math (abs, min, max, sqrt, sin, cos, floor, ceil, pow) and String (length, hashCode)
- [x] SIMD-optimized array copy: AVX2 for int[]/long[], AVX for float[]/double[], with `System.arraycopy` intrinsic
- [x] Compressed oops: 16-bit encoded references for heaps ≤ 65,535 objects (50% per-slot savings, alignment-shift support)

### Differentiation Features
- [x] Rust memory safety guarantees (no data races, use-after-free)
- [x] WebAssembly backend for browser/edge deployment
- [x] Deterministic execution mode for blockchain
- [x] C API for embedding in applications
- [x] Polyglot Java/Rust interop without JNI overhead
- [x] SIMD vectorization support
- [x] Async I/O integration with tokio
- [x] Time-travel debugging support

### Tooling
- [x] Integrated profiler with flame graphs
- [x] Security instrumentation
- [x] Visualization tools for heap and stack
- [x] Fuzz testing infrastructure

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## Reference

See `docs/competitive-differentiation.md` for detailed differentiation analysis.
See `ARCHITECTURE.md` for system architecture and design decisions.
See `benches/` for existing benchmark implementations.
