SILOptimizer: Fix mandatory switch dispatch elimination for unreachable cases #84680
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nkcsgexi
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xymus
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Oct 3, 2025
…le cases. swiftlang#67920 introduced a mandatory SIL optimization that eliminates switch statement dispatch for enum elements that are provably unavailable at runtime. This optimization helps eliminate unreachable code, but it's also load bearing because it removes references to enum element symbols that may not preset at link time. The optimization was checking the wrong condition to determine whether an enum element is unavailable at runtime and so the optimization wasn't working for code using custom availability domains. Resolves rdar://161846311.
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#67920 introduced a mandatory SIL optimization that eliminates switch statement dispatch for enum elements that are provably unavailable at runtime. This optimization helps eliminate unreachable code, but it's also load bearing because it removes references to enum element symbols that may not preset at link time. The optimization was checking the wrong condition to determine whether an enum element is unavailable at runtime and so the optimization wasn't working for code using custom availability domains.
Resolves rdar://161846311.