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[SR-9701] Stack allocated Objective-C no escape closures #52141

aschwaighofer opened this issue Jan 18, 2019 · 2 comments

[SR-9701] Stack allocated Objective-C no escape closures #52141

aschwaighofer opened this issue Jan 18, 2019 · 2 comments


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aschwaighofer commented Jan 18, 2019

Previous ID SR-9701
Radar None
Original Reporter @aschwaighofer
Type Improvement
Additional Detail from JIRA
Votes 0
Component/s Compiler
Labels Improvement
Assignee None
Priority Medium

md5: fd60c5edf6ddc3d03a27ac1f2a14393b

Issue Description:

When we pass closures to @NoEscape objective c block arguments the closures are allocated on the heap. We should also stack allocate them.

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belkadan commented Jan 23, 2019

The Objective-C convention is actually fine with you stack-allocating all block arguments; it's considered the callee's responsibility to Block_copy them. cc @rjmccall

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rjmccall commented Jan 23, 2019

Correct. We don't do this only because we're being cautious about lifetimes. If we had a reliable way of detecting that the copy is unnecessary, it would be a significant win.

Clang has actually implemented an optimization where it eliminates the copying logic from `noescape` blocks entirely, essentially generating them as global blocks that happen to be allocated on the stack.

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