Hidden Overhead of a Function API

on YouTube ↗01h 03m

" summary

Examines concrete assembly and microbenchmarks across Clang GCC and MSVC on ARM and x86 and shows how signature choices matter: returning by value usually beats output parameters (measured 25% overhead for an out-param case), wrappers like std::unique_ptr can force memory temps (one case is 3x slower), calling conventions and ABI rules explain stray loads and moves, a small lazy wrapper implementation restores RVO and eliminates the extra work, and all investigations use Compiler Explorer and real instruction counts.

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" chapters (17)

1. 0:00Introduction
2. 1:25Functions and performance
3. 3:12Performance beyond benchmarks
4. 7:06Return values vs output params
5. 12:51Return by value and C++ abstractions
6. 23:07Return value optimization deep dive
7. 28:15Output parameters in practice
8. 29:48Pass by value vs reference
9. 34:52Perfect forwarding costs
10. 35:54Non-trivial types and references
11. 36:17Span and trivial types
12. 39:30Empty params and ABI quirks
13. 43:04Parameter order and registers
14. 47:42Array pointer pitfalls
15. 50:34Limiting arguments for speed
16. 55:13Key takeaways
17. 56:41Q&A

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