How should toolchains apply shared?

[abrown]

As noted here, toolchains may have trouble identifying which parts of compiled objects should be marked shared and which not.

• Perhaps toolchains like LLVM should liberally apply shared everywhere once parallelism is suspected — but perhaps not. How should toolchains go about this?
• Also, it seems likely that users may want to have fine-grained control over what objects are declared as shared. What should this look like?

[conrad-watt]

I think, as a baseline, we'll need to assume at least some toolchains will want to do the automatic thing - so that push-button compilation of C applications using POSIX threads can be supported (my understanding is the Empscripten already provides this using the threads MVP). This probably means the toolchain either marking everything as shared or doing a transitive calculation (with reference to #4 for the problem of host interaction).