--llvm-lto 3 -s USE_PTHREADS -s FETCH=1 broken in 1.38.28

[VirtualTim]

Compiling something simple like:

#include <iostream>
int main(int argc, char** argv) {
	std::cout << "test" << std::endl;
}

Using: emcc test.cpp --llvm-lto 3 -s USE_PTHREADS -s FETCH=1 -o test.html Will result in the error
shared:ERROR: failed to find function _pthread_mutexattr_init!

This worked in 1.38.27. Compiling with -s WASM=0 doesn't change the error.
--llvm-lto 2 works for the above example, but the actual code I'm working on requires --llvm-lto 0 to compile.

[kripken]

Possibly a bug where we assume that function exists without adding an explicit export for it, and LTO manages to optimize it out in this case.

[VirtualTim]

_pthread_mutex_init also needs to be exported.

I thought I could add something like this shared.Settings.EXPORTED_RUNTIME_METHODS += ['_pthread_mutexattr_init', '_pthread_mutex_init']
around here: https://github.com/emscripten-core/emscripten/blob/incoming/emcc.py#L2067, but that didn't seem to change anything.
Adding '_pthread_mutexattr_init', '_pthread_mutex_init' to -s EXPORTED_FUNCTIONS fixes this.

[kripken]

What code calls those pthread mutex functions? If it was in the JS, then exporting would be the natural solution. I don't see that though. So we should find out where it's called, and understand why normal linking didn't bring those in.

[VirtualTim]

Not really sure how this all works, but these functions are called in the generated fetch.js, and looks like they should be imported here?
So I'm sure really sure how those get removed.

[kripken]

Ah, this might be related to the special fetch-worker stuff then. I think only @juj understands that code well. It would be good to rewrite that as a simple/normal pthread at some point.

[VirtualTim]

I think the fix is to add these to library_fetch.js, in a similar manner to #9202.
I don't have time right now to work on a PR, but I'll look at this in the future.

[stale]

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