bulbazord added inline comments.
================ Comment at: lldb/include/lldb/Core/Debugger.h:455-456 + InterruptionReport(std::string function_name, std::string description) : + m_function_name(function_name), + m_description(description), + m_interrupt_time(std::chrono::system_clock::now()), ---------------- jingham wrote: > bulbazord wrote: > > jingham wrote: > > > bulbazord wrote: > > > > To avoid some unnecessary copies > > > > > > > > Could also do what Ismail is suggesting. > > > This is a local that is copied to an ivar and never used again. Do I > > > really have to put move in there explicitly for the optimizer to know it > > > can reuse the value? > > Yes. I created a simple example on Godbolt: https://godbolt.org/z/G4ej76Enn > > > > Observe that the constructor in the example invokes the `std::string` copy > > constructor. Add a `std::move` and it then invokes the move constructor. > Thanks for the example, that was interesting. > > Note however that in your example, you the flags you specified were > `-std=c++17` so that was an unoptimized build. That's expected, unoptimized > builds are supposed to be as literal as they can be. If you instead use the > same example with `-std=c++17 -O3` you won't see any copy constructors. I > don't 100% mind putting this std::move in, but it seems noisy to decorate up > your code with hints that the optimizer can figure out on its own. You're right that I did not consider higher optimization levels there. That being said, I believe this is a matter of language semantics and not optimization level. I've created a slightly more complex example to illustrate: https://godbolt.org/z/naMTcd7Ev In this other example, I have passed `-O3`. You'll notice that in the emitted constructor code there are 2 calls to `operator new`. If you add `std::move` for both of the parameters of the constructor, both of these allocations go away and the generated code becomes ~60% smaller. Even with optimization involved, the compiler can only optimize so much without breaking semantics. Repository: rG LLVM Github Monorepo CHANGES SINCE LAST ACTION https://reviews.llvm.org/D154542/new/ https://reviews.llvm.org/D154542 _______________________________________________ lldb-commits mailing list lldb-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/lldb-commits
