275619 2024-06-18 09:29:49 -0700 Avoid copying of swift return values in Swift-Cpp interop 2024-06-20 14:02:44 -0700 1 1 1 Unclassified WebKit WebCore Misc. Other Unspecified Unspecified RESOLVED FIXED InRadar P2 Normal --- 1 nitinmahendru nitinmahendru webkit-bug-importer oldest_to_newest 2041891 0 nitinmahendru 2024-06-18 09:29:49 -0700 In the existing Swift-Cpp interop interface, when C++ tries to extract values out of swift structs, it generates a Copy. Even if we declare the same structure in C++ and construct it on swift side with std::optional in it, and then get the value on C++ side, it still generates a copy. The existing Cpp::makeOptional cannot be changed to take a rvalue reference to avoid the copying as interop does not support rvalue references. With the current interop features, the best solution for now is to remove optionals and return an empty vector in error scenarios. This should be a reasonable mitigation as the hot path "should" be success in which case the vector returned actually holds a useful value. In errors, yes, an empty vector will be returned(adding std::optional was a solution for that problem) but that seems to add extra copies which we would like to avoid if possible. 2041910 1 nitinmahendru 2024-06-18 10:51:30 -0700 <rdar://problem/129772363> 2041911 2 nitinmahendru 2024-06-18 10:52:49 -0700 Pull request: https://github.com/WebKit/WebKit/pull/29940 2042307 3 ews-feeder 2024-06-20 14:02:42 -0700 Committed 280218@main (20dee432499d): <https://commits.webkit.org/280218@main> Reviewed commits have been landed. Closing PR #29940 and removing active labels.