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[SR-13462] Existentials needlessly copied #55904

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dabrahams opened this issue Aug 27, 2020 · 2 comments
Open

[SR-13462] Existentials needlessly copied #55904

dabrahams opened this issue Aug 27, 2020 · 2 comments
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@eeckstein
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bug A deviation from expected or documented behavior. Also: expected but undesirable behavior. compiler The Swift compiler in itself

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@dabrahams
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Previous ID SR-13462
Radar rdar://problem/68116209
Original Reporter @dabrahams
Type Bug
Additional Detail from JIRA
Votes 0
Component/s Compiler
Labels Bug
Assignee @eeckstein
Priority Medium

md5: 4dd324f44e59e9bba4cd43da818fb481

Issue Description:

This program prints

true
false

but should print

true
true

`X` and `Y` are identical except that `Y` stores an `Any`.

struct X {
  var a: Int = 3

  func test() {
    let p0 = withUnsafePointer(to: self) { UnsafeRawPointer($0) }
    let p1 = withUnsafePointer(to: a) { UnsafeRawPointer($0) }
    print(p0 == p1)
    withExtendedLifetime(self) {}
  }
}

struct Y {
  var a: Any = 3

  func test() {
    let p0 = withUnsafePointer(to: self) { UnsafeRawPointer($0) }
    let p1 = withUnsafePointer(to: a) { UnsafeRawPointer($0) }
    print(p0 == p1)
    withExtendedLifetime(self) {}
  }
}

X().test()
Y().test()
@typesanitizer
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@eeckstein
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Sorry for the delay.
This test program is actually undefined behavior because it let the pointers escape from the closures.
The optimizer tends to give up in case it sees "unsafe" code like this.
Also, with a recent compiler, the output for X.test is false.

Is this just an artificial test case to show the problem? Do you have a more realistic test case without undefined behavior?

@swift-ci swift-ci transferred this issue from apple/swift-issues Apr 25, 2022
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@eeckstein eeckstein

Labels
bug A deviation from expected or documented behavior. Also: expected but undesirable behavior. compiler The Swift compiler in itself
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@dabrahams @typesanitizer @eeckstein