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[SR-3728] Explore using spare bits in references for ARC optimizations #46313

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ematejska mannequin opened this issue Jan 25, 2017 · 2 comments
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[SR-3728] Explore using spare bits in references for ARC optimizations #46313

ematejska mannequin opened this issue Jan 25, 2017 · 2 comments
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affects ABI Flag: Affects ABI task

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@ematejska
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Mannequin

ematejska mannequin commented Jan 25, 2017

Previous ID SR-3728
Radar rdar://problem/31411206
Original Reporter @ematejska
Type Task
Status Resolved
Resolution Won't Do
Additional Detail from JIRA
Votes 0
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Labels Task, AffectsABI
Assignee None
Priority Medium

md5: c2f9f85d68a6a079d894fbb5c1c7e156

Issue Description:

Ahead of ABI Stability, explore using spare bits in references to store local reference counts in order to perform some ARC operations more efficiently . These would need to be flushed to the object whenever a reference may escape or the local reference count reaches zero. If these local reference counts can cross ABI boundaries, then such a change will have to be implemented in an ABI-additive way with deployment target checking.
@bob-wilson
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@swift-ci create

@bob-wilson
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This could potentially give some big performance improvements, but it would be a lot of work to implement and it's not feasible to fit it into Swift 5. It is worth noting that this optimization is not needed for calls within a module, because we can get the same benefit there using function signature optimization.

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