SILGen plumbing for existential lvalue access fixes #9637
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This is an LValue component whose value is the class reference inside of a class existential. Unlike OpenOpaqueExistentialComponent, this is a logical component, with a "writeback" consisting of wrapping the new class reference in a class existential having the same conformances as the original. This is slightly awkward, but adding "by-address" operations on class existentials, and projecting the payload out is a big change and might not make sense for other reasons.
…s as lvalues This is part of allowing lvalue access on class existential payloads.
…ntials This is pretty awkward. If an lvalue has an open existential as its RValue type, we would emit an alloc_stack instruction holding the materialized temporary before we emitted the value itself. This introduced a def-after-use violation because the open existential type in the stack allocation was not dominated by its definition. To get around this, don't use an SGFContext to emit the 'get' in-place. There's no performance degradation, because the only time we will attempt materializing an lvalue with an open existential type is when performing an lvalue access of a class existential payload, and here we in-place initialization makes no difference since the value is a single reference.
…Exprs with lvalue base
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@swift-ci Please smoke test |
This was referenced May 23, 2017
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This is NFC for now -- there will also be a Sema change, which will introduce tests.