Week 21: Advanced Optimizations (Advanced)

Overview

Week 21 focuses on squeezing maximum performance out of Rust code through compiler optimizations and memory-level optimizations. You’ll learn how to leverage LLVM’s optimization capabilities, optimize memory layout and access patterns, and reduce allocation pressure for peak efficiency and throughput.

Day 1-3: Compiler Optimizations

Topics

• The Rust compilation process:
  • Rustc frontend
  • MIR (Mid-level Intermediate Representation)
  • LLVM backend
  • Optimization passes
  • Code generation
• LLVM optimization passes:
  • Understanding -C opt-level options
  • Function inlining
  • Loop optimizations
  • Constant propagation and folding
  • Dead code elimination
  • LLVM optimization flags
• Link-time optimization (LTO):
  • Thin LTO vs full LTO
  • Cross-module optimization
  • Setting up LTO in Cargo.toml
  • Trade-offs and build time impact
  • Measuring LTO effectiveness
• Profile-guided optimization (PGO):
  • Creating performance profiles
  • Instrumentation builds
  • Feed-forward optimization
  • Combined LTO+PGO approach
  • AutoFDO (Automatic Feedback-Directed Optimization)
• Rust-specific optimizations:
  • Monomorphization
  • Trait optimizations
  • Iterator optimizations
  • Bounds check elimination
  • Const evaluation and propagation

Resources

• Rust Performance Book: Compile-time Optimizations
• LLVM Optimization Guide
• LTO in Rust
• Rust and LLVM
• Profile Guided Optimization
• Compiler Explorer for Rust
• Rustc Dev Guide: LLVM Optimizations

Use Cases

• Performance-critical applications
• Reducing binary size
• Embedded systems optimization
• Game engines
• Real-time processing systems
• High-frequency trading
• Computational libraries

Day 4-7: Memory Optimizations

Topics

• Cache-friendly data structures:
  • CPU cache hierarchy
  • Cache line optimization
  • Spatial and temporal locality
  • Structure of Arrays (SoA) vs Array of Structures (AoS)
  • False sharing avoidance
• Memory layout optimization:
  • Structure packing and alignment
  • Field ordering for size reduction
  • Enum optimization
  • Zero-sized type optimization
  • Custom DSTs (Dynamically Sized Types)
• Allocation strategies:
  • Stack vs heap allocation tradeoffs
  • Pre-allocation and capacity management
  • Object pooling
  • Arena allocation patterns
  • Small string/vector optimizations
• Reducing allocation pressure:
  • In-place operations
  • Reusing allocations
  • Custom allocators
  • Bump allocators for short-lived objects
  • Preventing heap fragmentation
• Advanced techniques:
  • Bit packing and compression
  • Memory mapping for large datasets
  • Custom slicing and chunking
  • Memory prefetching
  • Non-temporal stores

Resources

• What Every Programmer Should Know About Memory
• Rust struct layout optimization
• Allocation API in Rust
• Memory Optimization Techniques
• Bumpalo Allocator
• Rust Container Cheat Sheet
• CPU Cache Effects

Use Cases

• Memory-constrained environments
• High-throughput data processing
• Real-time systems with strict latency requirements
• Large data structures
• High-frequency event handling
• Long-running applications
• Embedded systems

Exercises

1. Use LLVM optimization flags to improve performance of a computationally intensive function
2. Implement LTO and PGO for a Rust application and measure the performance improvement
3. Redesign a data structure for better cache locality and measure the impact
4. Create a custom allocator optimized for a specific workload
5. Implement an object pool pattern for frequently allocated/deallocated objects
6. Optimize a struct’s memory layout by reordering fields and using appropriate types

Advanced Challenges

1. Create a benchmark comparing different memory layout strategies for a specific algorithm
2. Implement a LLVM optimization pass targeting a specific Rust pattern
3. Build a high-performance, cache-optimized data structure for a specialized use case
4. Create a memory profiler that suggests layout optimizations
5. Develop a custom PGO workflow for a complex application

Next Steps

After completing Week 21, you’ll have a deep understanding of performance optimization techniques at both the compiler and memory level. Week 22 will shift focus to WebAssembly, exploring how to use Rust to build high-performance web applications.