Open
Description
| Previous ID | SR-10708 |
| Radar | None |
| Original Reporter | @drexin |
| Type | Bug |
Attachment: Download
Environment
Apple Swift version 5.0 (swift-5.0-RELEASE)
Target: x86_64-apple-darwin18.5.0
Additional Detail from JIRA
| Votes | 1 |
| Component/s | Compiler |
| Labels | Bug, 5.0Regression, ARC, Optimizer |
| Assignee | None |
| Priority | Medium |
md5: c994e96b09804105727b513a51ebc355
relates to:
- SR-10709 Swift needs allocation counter tests
Issue Description:
When switching over the result of a dictionary lookup directly in Swift 5 and then modifying that dictionary it will be copied.
class Foo {
var dict: [String: Int] = ["x": 1]
func test(_ x: String) {
switch dict[x] {
case .some(let y):
dict[x] = y
default: ()
}
}
}
let foo = Foo()
for _ in 1 ... 1000 {
foo.test("x")
}The above code allocates 1092 times in total.
When assigning the result to a variable first, it does not copy.
class Foo {
var dict: [String: Int] = ["x": 1]
func test(_ x: String) {
let value = dict[x]
switch value {
case .some(let y):
dict[x] = y
default: ()
}
}
}
let foo = Foo()
for _ in 1 ... 1000 {
foo.test("x")
}The above code allocates 91 times in total.
In Swift 4.2 both versions do not copy, so this seems to be a regression in Swift 5.