prevent reinitialization of self after discard
#66351
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The value `self` is mutable (i.e., var-bound) in a `consuming` method. Since you're allowed to reinitialize a var after consuming, that means you were also naturally allowed to reinitialize self after `discard self`. But that capability was not intended; after you discard self you shouldn't be reinitializing it, as that's probably a mistake. This change makes reinitialization of `self` reachable from a `discard self` statement an error. rdar://106098163
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@swift-ci please smoke test |
gottesmm
approved these changes
Jun 6, 2023
| if (dropDeinits.empty() || reinits.empty()) | ||
| return; | ||
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| using BasicBlockMap = llvm::DenseMap<SILBasicBlock *, |
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Don't worry about making this change in this patch. But for future reference you can use a Small FrozenMultiMap in situations like this. It is less heavy weight than an llvm DenseMap (which always heap allocates 64 entries). A small frozen multi-map is an array that you initialize with key value pairs that is when it is frozen stable sorted by the first element. So you get a map from Key -> [Value] and it can be in small form.
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@kavon here is a link to FrozenMultiMap for your perusal.
swift/include/swift/Basic/FrozenMultiMap.h
Line 15 in
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The value
selfis mutable (i.e., var-bound) ina
consumingmethod. Since you're allowed toreinitialize a var after consuming, that means
you were also naturally allowed to reinitialize
self after
discard self. But that capability was not intended; after you discard self you shouldn't be reinitializing it, as that's probably a mistake.This change makes reinitialization of
selfreachable from a
discard selfstatement an error.rdar://106098163