Allan Shortlidge e2bb7e8c8b SILOptimizer: Remove switch cases matching unavailable enum elements. ...

Unavailable enum elements cannot be instantiated at runtime without invoking
UB. Therefore the optimizer can consider a basic block unreachable if its only
predecessor is a block that terminates in a switch instruction matching an
unavailable enum element. Furthermore, removing the switch instruction cases
that refer to unavailable enum elements is _mandatory_ when
`-unavailable-decl-optimization=complete` is specified because otherwise
lowered IR for these instructions could refer to enum tag accessors that will
not be lowered, resulting in a failure during linking.

Resolves rdar://113872720.

2023-08-15 17:13:10 -07:00

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