[Next][Cherry-pick][DebugInfo] Add num_extra_inhabitants to debug info (#112590) #9536
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An extra inhabitant is a bit pattern that does not represent a valid value for instances of a given type. The number of extra inhabitants is the number of those bit configurations. This is used by Swift to save space when composing types. For example, because Bool only needs 2 bit patterns to represent all of its values (true and false), an Optional<Bool> only occupies 1 byte in memory by using a bit configuration that is unused by Bool. Which bit patterns are unused are part of the ABI of the language. Since Swift generics are not monomorphized, by using dynamic libraries you can have generic types whose size, alignment, etc, are known only at runtime (which is why this feature is needed). This patch adds num_extra_inhabitants to LLVM-IR debug info and in DWARF as an Apple extension. (cherry picked from commit f6617d6) (cherry picked from commit cdc3876)
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An extra inhabitant is a bit pattern that does not represent a valid value for instances of a given type. The number of extra inhabitants is the number of those bit configurations.
This is used by Swift to save space when composing types. For example, because Bool only needs 2 bit patterns to represent all of its values (true and false), an Optional only occupies 1 byte in memory by using a bit configuration that is unused by Bool. Which bit patterns are unused are part of the ABI of the language.
Since Swift generics are not monomorphized, by using dynamic libraries you can have generic types whose size, alignment, etc, are known only at runtime (which is why this feature is needed).
This patch adds num_extra_inhabitants to LLVM-IR debug info and in DWARF as an Apple extension.
(cherry picked from commit f6617d6) (cherry picked from commit cdc3876)