Popular：
Virtualization DNS security formal verification reachability analysis compiler errors macro conflict web extension development framework Bitmap Graphics API inconsistencies All Tags

Exploiting Constraints for Significant Performance Gains: Optimizing Even Number Counting in C++

2025-03-09

This article explores optimizing the performance of counting even numbers in a uint8_t array in C++. By comparing two approaches—using `std::count_if` and a custom counting function—the author demonstrates that the custom function, leveraging the constraint that the number of even values is between 0 and 255, significantly improves performance, achieving up to a 9.5x speedup in tests. The article analyzes the assembly code generated by both methods, explaining the performance difference, and mentions a vectorization issue in specific GCC versions.

Read more
(nicula.xyz)
Development C++ optimization vectorization

Clang Optimization Regression: Inlining Backfires in C++ Benchmark

2025-02-19

A C++ benchmark revealed a performance regression in Clang's optimization of inline functions. When the `increment` function was inlined, branch prediction failures resulted in roughly a 5x slowdown compared to the non-inlined version. `perf stat` confirmed branch mispredictions as the culprit. Interestingly, compiling with the Zig toolchain significantly improved performance, suggesting a potential regression in Clang 19. The issue has been reported on the Clang/LLVM repository, with initial investigation pointing to a trade-off between SROA and SimplifyCFG optimization passes.

Read more
(nicula.xyz)
Development