Hi all, We now have link-time optimization (LTO) between Rust and C++ code enabled on Nightly for all platforms (bug 1486042 [1]). There have been some concerns about potential slowdowns when crossing the C++ <=> Rust boundary due to non-inlineable function calls, and Stylo needed to implement some gnarly code copying between C++ and Rust to obtain good performance. With cross-language LTO enabled, such concerns and hacks should become a thing of the past.
It is worth explicitly noting that enabling this feature does not seem to have made much difference on our performance tests: if you are doing performance work, you should *not* need to enable this feature. (Which is a good thing, as it massively increases the amount of time needed to link libxul...) The primary benefit at the moment is not having to implement code on both the C++ and Rust side as Stylo did and to eliminate concerns that crossing the language boundary induces a performance issue. Please note that if you attempt to build your own cross-language LTO-enabled binary on OS X, your binary will be broken in interesting ways due to bugs in Xcode. Work to error out much earlier in that configuration is happening in bug 1563204 [2]. There were a number of people involved in this effort: Michael Woerister did the Rust-side work [3]. David Major did the initial landing for Win64 only [4]. Michael fixed some issues in bindgen that prevented Win32 from working correctly [5]. And Mike Hommey tied up loose ends and pushed things over the line while I was away for the last two weeks. Thanks to all involved! -Nathan [1] https://bugzilla.mozilla.org/show_bug.cgi?id=1486042 [2] https://bugzilla.mozilla.org/show_bug.cgi?id=1563204 [3] https://github.com/rust-lang/rust/issues/49879 [4] https://bugzilla.mozilla.org/show_bug.cgi?id=1512723 [5] https://github.com/rust-lang/rust-bindgen/pull/1558 _______________________________________________ dev-platform mailing list dev-platform@lists.mozilla.org https://lists.mozilla.org/listinfo/dev-platform
