Order file generation appears to be supported by clang via
-cc1 -forder-file-instrumentation, and in turn LLVM has an option
--enable-order-file-instrumentation. Is this option currently supported for swiftc via
-Xllvm? If not, it would be great to have it, or better yet a flag within swiftc. I've seen order files reduce startup time by ~5% for large apps.
Note that there is support in swiftc to instrument all function calls with
-sanitize-coverage but using it for order file generation is much less convenient and obvious.