introduce @_manualOwnership performance attribute #81858
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This attribute forces programmers to acknowledge every copy that is required to happen in the body of the function. Only those copies that make sense according to Swift's ownership rules should be "required". The way this is implemented as of now is to flag each non-explicit copy in a function, coming from SILGen, as an error through PerformanceDiagnostics.
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This attribute forces programmers to acknowledge every copy that is required in the body of a function. The copies that are "required" to be acknowledged are those that are implicit according to Swift's core language implementation rules. For example,
passing a value to a consuming parameter does not require explicitly copying the argument in the source language, but by the ownership rules a copy will happen. Acknowledging copies does not impact performance and these copies are a superset of all copies that will happen in the function; they are still eligible be eliminated by optimizations.
The way this is implemented is to flag every implicitly-created copy in such functions as an error. This ensures programmers and the compiler are in sync about what copies are actually happening. This motivates performance conscious programmers to write their code in such a way to avoid copies. It also motivates fixes in the compiler for cases where it is emitting a copy that is useless according to the language.
Related to rdar://151323307