Runtime: Less eager instantiation of type metadata in the conformance cache #29887
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slavapestov
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mikeash
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Feb 17, 2020
… cache The ConformanceCandidate constructor would eagerly instantiate metadata for all non-generic types in the conformance cache. This was not the intention of the code though, because it can compare nominal type descriptors -- which are emitted statically -- for those types that have them, namely everything except for foreign and Objective-C classes. Change the order of two calls so that the lazy path has a chance to run. This fixes a crash when type metadata uses weakly-linked symbols which are not available, which can come up in backward deployment scenarios. Fixes <rdar://problem/59460603>.
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jckarter
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Apr 24, 2020
…ache. The runtime that shipped with Swift 5.1 and earlier had a bug that interfered with backward deployment of binaries that dynamically check for protocol conformances on conditionally-available tests. This was fixed in the top-of-tree Swift runtime by swiftlang#29887; however, that doesn't do much good for running binaries on older OSes that don't have that fix. In order for binaries built with a newer Swift compiler to run successfully on older OSes, introduce a compatibility hook that replaces the conformance cache implementation in the original OS runtime with a version based on the current implementation that has the fix for the protocol conformance bug. Fixes rdar://problem/59460603
jckarter
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Apr 24, 2020
…ache. The runtime that shipped with Swift 5.1 and earlier had a bug that interfered with backward deployment of binaries that dynamically check for protocol conformances on conditionally-available tests. This was fixed in the top-of-tree Swift runtime by swiftlang#29887; however, that doesn't do much good for running binaries on older OSes that don't have that fix. In order for binaries built with a newer Swift compiler to run successfully on older OSes, introduce a compatibility hook that replaces the conformance cache implementation in the original OS runtime with a version based on the current implementation that has the fix for the protocol conformance bug. Fixes rdar://problem/59460603
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The ConformanceCandidate constructor would eagerly instantiate metadata for
all non-generic types in the conformance cache. This was not the intention
of the code though, because it can compare nominal type descriptors --
which are emitted statically -- for those types that have them, namely
everything except for foreign and Objective-C classes.
Change the order of two calls so that the lazy path has a chance to run.
This fixes a crash when type metadata uses weakly-linked symbols
which are not available, which can come up in backward deployment
scenarios.
Fixes rdar://problem/59460603.