Implement a syntactic peephole for reversing implicit bridging conversions #10987
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Previously, we sometimes built optional injections and evaluations on the outside. NFC, but it makes the bridging peephole a lot simpler.
a known-non-empty state to a known-empty state.
create a tuple of argument sources, and destructure such tuples during argument emission. NFC.
conversions that reverse an implicit conversion done to align foreign declarations with their imported types. For example, consider an Objective-C method that returns an NSString*: - (nonnull NSString*) foo; This will be imported into Swift as a method returning a String: func foo() -> String A call to this method will implicitly convert the result to String behind the scenes. If the user then casts the result back to NSString*, that would normally be compiled as an additional conversion. The compiler cannot simply eliminate the conversion because that is not necessarily semantically equivalent. This peephole recognizes as-casts that immediately reverse a bridging conversion as a special case and gives them special power to eliminate both conversions. For example, 'foo() as NSString' will simply return the original return value. In addition to call results, this also applies to call arguments, property accesses, and subscript accesses.
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@swift-ci Please test and merge. |
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This appears to be the cause of source compatibility suite failures https://ci.swift.org/view/Source%20Compatibility/job/swift-master-source-compat-suite/802/ I will revert if local testing confirms it. See also rdar://33341584 |
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