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GuaranteedPhiUpdater: fix a comment #77582

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Nov 13, 2024
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GuaranteedPhiUpdater: fix a comment #77582

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9 changes: 5 additions & 4 deletions SwiftCompilerSources/Sources/Optimizer/Utilities/GuaranteedPhiUpdater.swift
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Original file line number Diff line number Diff line change
Expand Up @@ -85,11 +85,12 @@ func updateReborrowFlags(in function: Function, _ context: some MutatingContext)
}

/// Updates the reborrow flags for all `phis`.
///
/// Re-borrow flags are only set, but never cleared. If an optimization creates a dead-end block
/// by cutting off the control flow before an `end_borrow`, the re-borrow flags still have to remain
/// without the possibility to re-calculate them from the (now missing) `end_borrow`.
///
func updateReborrowFlags(for phis: some Sequence<Phi>, _ context: some MutatingContext) {
// TODO: clear reborrow flags before re-computing when we have complete OSSA lifetimes.
// It would be cleaner to first clear all flags. But this is not possible because some end_borrow instructions
// might be missing in dead-end blocks. This will be fixed with complete OSSA lifetimes.

if let phi = phis.first(where: { phi in true }), !phi.value.parentFunction.hasOwnership {
return
}
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