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[SR-14158] Nondeterminism on macOS for C struct identity #56537

swift-ci opened this issue Feb 5, 2021 · 0 comments

[SR-14158] Nondeterminism on macOS for C struct identity #56537

swift-ci opened this issue Feb 5, 2021 · 0 comments


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@swift-ci swift-ci commented Feb 5, 2021

Previous ID SR-14158
Radar None
Original Reporter george (JIRA User)
Type Bug
Additional Detail from JIRA
Votes 0
Component/s Compiler
Labels Bug
Assignee None
Priority Medium

md5: c5751a191ee27027a9454fdb6641ece3

Issue Description:

Update: it seems like removing any references to the `MlirDialectRegistrationHooks` is an effective workaround for this issue. This is just speculation, but this seems to imply that the issue is the hashing strategy which seems like it is used to determine C struct identity has a nondeterminism on macOS. For more discussion, consult this forum thread:

The project where this occurred is open source, and the GitHub Action output can be found here:

Basically, I have a project with three system library targets, each of which ends up including a C header file "Registration.h". When building a target that depends on more than one of these libraries, compilation fails on macOS but not Linux reporting the following error:

Registration.h:64:31: error: 'MlirDialectRegistrationHooks' has different definitions in different modules; first difference is definition in module 'CSCF' found field 'getNamespaceHook' with type 'MlirDialectGetNamespaceHook' (aka 'struct MlirStringRef ()')
MlirDialectGetNamespaceHook getNamespaceHook;
Registration.h:64:31: note: but in 'CMLIR' found field 'getNamespaceHook' with type 'MlirDialectGetNamespaceHook' (aka 'struct MlirStringRef ()')
MlirDialectGetNamespaceHook getNamespaceHook;

Curiously, there are other `structs` defined in header files that are imported by both (the typedefs in IR.h are a good example) and these work fine, it is just `MlirDialectRegistrationHooks` that causes the problem. Removing references to `MlirDialectRegistrationHooks` in the Swift code fixes the issue.

Update: Running a few more tests revealed that the failure indeed is intermittent. I have been able to successfully build using both Xcode and Swift Package Manager on macOS (I have not been able to get it to fail on Linux), and I have been able to cause both to fail with the error above. This makes me believe this is a race condition. Perhaps there is some code which unifies definitions imported from different C libraries, but isn't properly synchronized.

@swift-ci swift-ci transferred this issue from apple/swift-issues Apr 25, 2022
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