> On Sep 14, 2016, at 10:25 AM, Ted Kremenek via swift-dev > <swift-dev@swift.org> wrote: > > Hi everyone, > > Joe Shajrawi nominated an optimizer fix for Swift 3.0.1 where the optimizer > was crashing due to duplicate conditions in aswitchstatement: > > https://bugs.swift.org/browse/SR-2512 <https://bugs.swift.org/browse/SR-2512> > https://github.com/apple/swift/pull/4747 > <https://github.com/apple/swift/pull/4747> > Here’s an example: > > public enum DemoEnum { > case firstCase > case secondCase > > public static func performSwitch(with value: Int) -> DemoEnum { > switch value { > case 0: > return DemoEnum.firstCase > case 0: > return DemoEnum.firstCase > default: > return DemoEnum.secondCase > } > } > } > I can’t remember why the frontend even accepts this code. Is this intended, > or just a defect in the compiler’s validity checking ofswitch statements? > >
It would be legitimate with, say, a condition on the first case. But yeah, this is undoubtedly just a defect in the compiler's checking. Recall that a switch in Swift doesn't necessarily compile to a primitive switch; it's more like a series of ifs that's a bit more straightforward to optimize matching for. So the validity checking you'd expect as a matter of course in C doesn't just fall out automatically. Also, of course, the compiler does not have primitive knowledge of Int or how it forms literals. John. > Thanks, > Ted > > _______________________________________________ > swift-dev mailing list > swift-dev@swift.org > https://lists.swift.org/mailman/listinfo/swift-dev
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