Neoclassical C++: segmented iterators revisited
2 days ago
- #Performance Optimization
- #Segmented Iterators
- #C++
- STL's design philosophy emphasizes near-zero overhead for abstractions, leading to efficient generic programming.
- Matt Austern's paper introduced segmented iterators to improve performance for naturally segmented data structures like deque by enabling hierarchical algorithms.
- Segmented iterators decompose into segment iterators (outer sequence) and local iterators (inner range), allowing algorithms to operate efficiently on contiguous segments.
- A segmented_iterator_traits template provides primitives for segmentation-aware algorithms, such as hierarchical_fill, which can yield significant performance gains.
- Boost.Container is experimenting with segmented algorithms, showing performance improvements, especially for small types where compilers can auto-vectorize local iterators.
- Benchmarks reveal up to 5.93x speedup for segmented vs. non-segmented algorithms on deque, with variations across compilers and element types.
- Unroll hints affect performance differently by compiler: beneficial for GCC, regressive for Clang, and neutral for MSVC.
- The ideas from Austern's paper remain relevant, demonstrating that well-designed abstractions can age gracefully with hardware improvements.