6.1: [OSSACompleteLifetime] Recurse into scoped addresses. #78207
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In preparation to expand it.
Previously, when determining and completing lifetimes of scoped
addresses, `computeTransitiveLiveness` was used to determine the
liveness used for completing the lifetime.
That approach had two problems:
(1) The function does not find scope-ending uses of `load_borrow`s.
The result was determining that the lifetime of the enclosing
`store_borrow` ended before that of the `load_borrow`.
(2) The function did not complete lifetimes of values defined within the
scoped address whose lifetimes the scoped address had to contain.
This was an inconsistency between the handling of scoped addresses
and that of values.
Here, both are addressed by implementing a `TransitiveAddressWalker` (as
`computeTransitiveLiveness`'s callee does) which not only visits
existing `end_borrow`s of `load_borrows` but completes them (and other
inner guaranteed values or scoped addresses).
rdar://141246601
On main type annotations are not always required but on 6.1 they are.
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@swift-ci please test |
tbkka
approved these changes
Dec 16, 2024
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Explanation: Fix lifetime completion of scoped addresses.
In #78081 , support for completing lifetimes of scoped addresses (
store_borrow,begin_access) was added. That support relied on theScopedAddressValue::computeTransitiveLivenessfunction, however. That function does not actually produce liveness that includes all transitive uses: specifically, it doesn't include theend_borrows ofload_borrows. The result was that lifetimes of scoped addresses would be ended before the lifetimes ofload_borrows that they enclose, which is invalid.Here, this is fixed by writing a variation of
computeTransitiveLiveness's calleefindTransitiveUsesForAddress. Like the latter, the new variation (written directly inOSSALifetimeCompletion) uses aTransitiveAddressWalker. Unlike it, however, it includes theend_borrows ofload_borrows.Additionally, the new walker completes inner lifetimes that are discovered while visiting the transitive uses of the scoped address. That brings this case into parity with what's done when completing lifetimes for values.
Scope: Affects optimized code.
Issue: rdar://141246601
Original PR: #78180
Risk: Low.
Testing: Added test.
Reviewer: Meghana Gupta ( @meg-gupta )