Extend borrow accessor support #84595
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Also add forGuaranteedAddressReturn
Introduce copy_value + mark_unresolved_non_copyable_value + begin_borrow at the return value of borrow accessor apply to drive move-only diagnostics. Also strip the copy_value + mark_unresolved_non_copyable_value + begin_borrow trio in a few places, since they create an artificial scope out of which we cannot return values in a borrow accessor without resorting to unsafe SIL operations currently. Borrow accessor diagnostics allow stripping these instructions safely in the following places: - return value of a borrow accessor - self argument reference in the borrow accessor return expression and borrow accessor apply
It can be used in borrow/mutate accessors to unsafely specify that the result is dependent on the self access.
Under library evolution, loadable self arguments are passed as @in_guaranteed. SILGen generates load_borrow for such self arguments proactively. load_borrow creates an artifical scope and returning values produced within this scope will be illegal without resorting to unsafe operations today. This change avoids creating a load_borrow proactively for borrow accessors.
…n a local borrow Borrow accessor result can sometimes be generated from a local borrow and returning the result produced within the local borrow scope will cause ownership errors. We have to introduce new SIL semantics to make this possible. Until then use a pair of unchecked_ownership_conversion instructions to silence the ownership errors. We encounter this when we have: Address-only self and @guaranteed result Loadable self and @guaranteed result derived from an unsafe pointer stored property This change also updates the result convention of borrow accessors with loadable result types and indirect self argument type.
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This PR adds IRGen support and enables writing borrow accessors for ~Copyable types and library evolution.
It also introduces interim
@_unsafeSelfDependentResultattribute to enable writing borrow accessors for unsafe pointer based containers.Borrow accessor result can sometimes be generated from a local borrow and returning the result produced within the
local borrow scope will cause ownership errors. This PR works around this issue for ~Copyable types and library evolution. But for nested borrow accessors that return
@guaranteedvalues with an@in_guaranteedself, I introduce a pair ofunchecked_ownership_conversioninstructions to silence the ownership errors. This is needed until we define new SIL semantics that allows returning values produced within local borrow scopes in borrow accessors.