Andrew Trick c3de120ca5 LifetimeDependence: simplify and fix multiple bugs. ...

Functional changes:

Improved modeling of dependence on local variable scopes.

For nested modify->read accesses, only extend the read accesses.

Avoid making a read access dependent on an inout argument.
The following needs to be an error to prevent span storage from being modified:

  @lifetime(owner)
  foo(owner: inout Owner) -> Span {
    owner.span
  }

Improve usability of borrowing trivial values (UnsafePointer). Allow:

  let span = Span(buffer.baseAddress)

Ignore access scopes for trivial values.

Structural changes:

Delete the LifetimeDependenceUseDefWalker.

Encapsulate all logic for variable introducers within the LifetimeDependenceInsertion pass. Once mark_dependence instructions are inserted, no subsequent pass needs to think about the "root" of a dependence.

Fixes: rdar://142451725 (Escape analysis fails with mutations)

2025-02-10 09:11:22 -08:00

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