ProfileSwiftUI gives you improved visibility of where CPU is being consumed inside your SwiftUI app. To use, add the ProfileSwiftUI Swift Package then import it and put something like the following in your RootView to setup logging then start polling statistics:
init() {
ProfileSwiftUI.profile(interval: 10, top: 5)
}
Output is rather verbose as it also logs calls SwiftUI makes internally to the "AttributeGraph" framework on which SwiftUI is based though these can be filtered out by passing a regex. (they will still appear in the periodic profile summary). The output is grouped by the function being called with detail entries breaking down where the function was called from.
At the interface between your app and the SwiftUI framework, methods inside SwiftUI are dispatched indirectly through a form of lookup using a writable area of memory (this is the standard means by which the Darwin dynamic linker "binds" between frameworks). Using the fishhook library is is possible to update this dispatch table by symbol name and "rebind" or "interpose" any implementation you would like of these functions.
The SwiftTrace library allows you to generate a logging aspect (trampoline) around each function call which you can interpose these to take the place of the original call destination. To log calls to AttributeGraph a second set of interposes is made on the SwiftUI libray where it calls out. For whatever reason this second interpose only works in the simulator.