IRGen: Fix enum lowering with -enable-resilience-bypass [4.2-04-30-2018] #16528
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The layout of an enum type will only use spare bits if the payload types have a fixed size in all resilience domains where they are visible. In practice, this means that: - If the enum is internal or resilient, we can use spare bits if the payload types are fixed size from inside the current module. - If the enum is public and not resilient, we can use spare bits if the payload types are fixed size from all resilience domains. The bug was that the 'fixed size in all resilience domains' check was returning true for resilient types when the -enable-resilience-bypass flag was on. This is wrong, because this meant that building a module with and without -enable-resilience-bypass could produce different lowerings for enum types. Fixes <rdar://problem/40034143>.
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@swift-ci Please test |
slavapestov
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Description: lldb does not (yet) support resilient value types, so it uses a special frontend flag where resilience is bypassed and exact type layouts are computed from the swiftmodule file. However in one corner case, resilient and non-resilient enums could actually get different layouts if the resilient case was able to make use of spare bits because the payload types had known layouts from inside the module. This patch fixes the resilience bypass to compute the correct enum layout in this case.
Origination: Introduced when resilience was enabled by default for the stdlib and overlays, making some value types defined in overlays resilient.
Scope of the issue: Manifests as a runtime crash when manipulating multi-payload enums from lldb, Swift REPL or Playgrounds.
Risk: Low, this changes a code path that is only hit in the above cases.
Reviewed by: @jrose-apple reviewed the change on swift-4.2-branch already.
Tested: New test case added.
Radar: rdar://problem/40034143