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https://github.com/apple/swift.git
synced 2026-10-24 20:15:56 +02:00
Meghana Gupta
8b3f775673
`LifetimeDependenceScopeFixup` can insert `end_cow_mutation_addr` on a struct address containing multiple COW fields, `SimplifyEndCOWMutationAddr` lowers it to an `end_cow_mutation` on the struct. `skipStructAndExtract()` in COWOpts was unconditionally looking through `struct_extract` and `destructure_struct` instructions when tracing from `begin_cow_mutation` back to `end_cow_mutation`. COWOpts would then trace from a `begin_cow_mutation` on one field, through `struct_extract`, to the `end_cow_mutation` on the `struct` that was placed for a different field's mutation. This caused COWOpts to incorrectly conclude the buffer was uniquely referenced and fold the uniqueness check to true, breaking COW semantics. The fix restricts `skipStructAndExtract` to only look through `struct_extract` and `destructure_struct` when the struct type has exactly one stored property. Resolves rdar://172670647
40 lines
698 B
Swift
40 lines
698 B
Swift
// RUN: %target-run-simple-swift(-O)
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// REQUIRES: executable_test
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struct S {
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var c: ContiguousArray<Int>
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var a: ContiguousArray<UInt64>
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var b: ContiguousArray<UInt64>
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init(n: Int) {
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c = .init(repeating: 0, count: n)
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a = .init(repeating: 0, count: n)
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b = .init(repeating: 0, count: n)
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}
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mutating func bump(n: Int) {
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do {
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var s = a.mutableSpan
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for i in 0 ..< n { s[i] &+= 1 }
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}
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do {
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var s = b.mutableSpan
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for i in 0 ..< n { s[i] &+= 1 }
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}
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}
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}
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@inline(never)
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func run() -> (UInt64, UInt64) {
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var x = S(n: 3)
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let snapshot = Array(x.b)
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x.bump(n: 3)
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return (x.b[0], snapshot[0])
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}
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let (a, b) = run()
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precondition(a != b)
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