c thomas howell CppCon 2018: Arthur O'Dwyer “Return Value Optimization: Harder Than It Looks”

http://CppCon.org
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Presentation Slides, PDFs, Source Code and other presenter materials are available at: https://github.com/CppCon/CppCon2018
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Join Arthur O'Dwyer on a deep dive into Return Value Optimization and related topics.

Even C++03 allowed the compiler to "elide" copy construction in certain cases. We'll start with an explanation of the calling convention on a typical machine, showing where the mysterious "return slot" lives, and why it makes sense that C++03 allowed copy elision in certain special cases (but not others). Then we'll show how C++11 (and a subsequent defect report) upped the game by quietly turning the remaining copies into moves, so that the commonly received wisdom these days is that `return std::move(x)` is never necessary and often a pessimization.

...Or is it? We'll show some real-world examples where `return x` quietly copies a large object instead of moving it. We'll explain the little-known notion of a "converting constructor", contrast it with "conversion operator", and show the precise way in which C++17 drops the ball on these examples. Finally, Arthur implemented a Clang compiler warning to detect and suggest fixes for problematic return statements; he'll walk through the relatively painless process of creating that diagnostic, and perhaps inspire you to contribute to Clang yourself!
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Arthur O'Dwyer

Arthur O'Dwyer started his career writing pre-C++11 compilers for Green Hills Software; he currently writes C++14 for Akamai Technologies. Arthur is the author of "Colossal Cave: The Board Game," "Mastering the C++17 STL" (the book), and "The STL From Scratch" (the training course). He is occasionally active on the C++ Standards Committee and has a blog mostly about C++.
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Videos Filmed & Edited by Bash Films: http://www.BashFilms.com

c thomas howell CppCon 2018: Arthur O'Dwyer “Return Value Optimization: Harder Than It Looks”
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