tools: disable ObjC for wasm in SILFunctionExtractor

[MaxDesiatov]

Currently, clang doesn't support Objective-C with the WebAssembly object format. Because of this, sil-function-extractor tool crashes in Clang's CGObjCCommonMac::GetSectionName function. Since Swift doesn't provide Objective-C interop for WebAssembly, it would make sense to disable it explicitly. sil-function-extractor is used in the test suite, so this PR is required for those tests to proceed when testing the WebAssembly toolchain and SDK.

Related to SR-9307.

(cc @compnerd)

[compnerd]

This really should mirror the behaviour from the driver -enable-objc-interop is a flag and is default enabled on Apple platforms and disabled on others. I think that sil-function-extractor could grow the same appendages.

[CodaFi]

Right. In general, Target.isOSDarwin(); is the predicate we want here.

[MaxDesiatov]

Would you prefer sil-function-extractor to have the same -enable-objc-interop flag, or should it just check Target.isOSDarwin() internally and flip EnableObjCInterop based on that?

[compnerd]

Both actually, it should have -enable-objc-interop to control the behaviour, but the default should be the value of Target.isOSDarwin().

[MaxDesiatov]

Thanks for the review, that's addressed now.

[MaxDesiatov]

@swift-ci please smoke test

[compnerd]

EnableObjCInterop should take precedent over Target.isOSDarwin(). That is, I should be able to disable ObjC interop even on Darwin.

[MaxDesiatov]

Is there any way to check if EnableObjCInterop was defined or not as a command-line argument? I had a look in LLVM docs, and looks like the only options for bool CL arguments are true or false (with false as the default) with no way to determine if it was explicitly passed or not.

[MaxDesiatov]

Got it, llvm::cl::boolOrDefault does the job.

[MaxDesiatov]

@swift-ci please smoke test

[CodaFi]

This looks pretty good. But can we match sil-opt where you can explicitly disable as well. https://github.com/apple/swift/blob/d5e5253cee0599a5362363d6ba0fe640493ea0e6/tools/sil-opt/SILOpt.cpp#L419

[MaxDesiatov]

@CodaFi were you looking at the old diff by any chance? With 2a220e1 that's exactly how it works, if I understand correctly. Or do you want to have a separate -disable-objc-interop option? That would be equivalent to -enable-objc-interop=false, which is already possible here. Would we want to have more than one way to explicitly disable it?

[MaxDesiatov]

@swift-ci please smoke test

[MaxDesiatov]

@swift-ci please smoke test Linux platform