NFC: Use createExportWrapper for exporting mangled symbols

[rth]

Closes #14695

This does reduce the size of the resulting .asm.js slightly (though it wasn't very conclusive in the use-case of Pyodide #14695 (comment)), and maybe the code paths are slightly more consistent with and without assertions.

Opening it just for reference. Happy to close it and the linked issue if you think it's not worth it.

[rth]

This does reduce the size of the resulting .asm.js slightly

To be more precise, for each exported symbol with delayed evaluation,

• before:

  var %(mangled)s = Module["%(mangled)s"] = function() {
     return (%(mangled)s = Module["%(mangled)s"] = Module["asm"]["%(name)s"]).apply(null, arguments);  
  };

  → 99 char + 4*len(mangled) + len(name)
• with this PR:

  createExportWrapper("{name}", "{mangled}");

  → 29 char + len(mangled) + len(name)

(numbers are approximate)

So for instance,

• in the case len(name) == len(mangled) - 1 == 6, that would be a 65% reduction in output size for these symbols
• if len(name) == len(mangled) - 1 == 50 , len(name) = 5, this would be a 62% reduction.

Hmm, I need re-check why I didn't see much impact on the total size on the example of Pyodide. Those exports do see take a significant amount of size (5k symbols).

[kripken]

Why is globalThis needed here? Aside from that, this PR looks very promising to me!

But it would also be good to see why this doesn't help pyodide - seems like it should.

[stale]

This issue has been automatically marked as stale because there has been no activity in the past year. It will be closed automatically if no further activity occurs in the next 30 days. Feel free to re-open at any time if this issue is still relevant.