Method descriptors #19067
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Method descriptors #19067
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rjmccall
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Aug 31, 2018
lib/IRGen/GenMeta.cpp
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| @@ -1207,12 +1218,14 @@ namespace { | |||
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| SILVTable *VTable = nullptr; | |||
| unsigned VTableSize = 0; | |||
| bool isResilient; | |||
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When we define type metadata, the 'full' symbol points at the entire struct, whereas the 'address point' symbol points at an offset inside. The logic for setting this up is a bit tricky because the 'address point' symbol may have been forward declared, and has to be replaced.
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Nominal type descriptors for protocols and classes contain an array of method descriptors. This PR defines symbols pointing at these descriptors, allowing them to be referenced from outside the module.
Method descriptors will be used in two places:
Resilient witness tables. Previously resilient witness tables used protocol dispatch thunks as keys, but this is problematic because we don't want to rely on function pointer identity.
Resilient method overrides. Here again we don't want to use dispatch thunks as keys; classes have the additional issue that resilient overrides are sometimes needed for methods that don't have dispatch thunks.