On Mon, Oct 14, 2019 at 9:05 AM Gerald Squelart <gsquel...@mozilla.com> wrote: > > I'm in the middle of watching Chandler Carruth's CppCon talk "There Are No > Zero-Cost Abstractions" and there's this interesting insight: > https://youtu.be/rHIkrotSwcc?t=1041 > > The spoiler is already in the title (sorry!), which is that passing > std::unique_ptr by value is more expensive than passing it by rvalue > reference, even with no exceptions! > > I wrote the same example using our own mozilla::UniquePtr, and got the same > result: https://godbolt.org/z/-FVMcV (by-value on the left, by-rref on the > right.) > So I certainly need to recalibrate my gutfeelometer.
The discussion in the talk about what is needed to fix this strongly suggested (without uttering "Rust") that Rust might be getting this right. With panic=abort, Rust gets this right ( https://rust.godbolt.org/z/SZQaAS ) which really makes one appreciate both Rust-style move semantics and the explicitly not-committal ABI. (I had to put a side-effectful println! in bar to make sure a call to bar is generated, since #[inline(never)] isn't enough to prevent the compiler from eliding calls to functions it can see do nothing.) -- Henri Sivonen hsivo...@mozilla.com _______________________________________________ dev-platform mailing list dev-platform@lists.mozilla.org https://lists.mozilla.org/listinfo/dev-platform
