This issue tracks part of our shrinking initiative, which is Option 1 from #5794. The goal is to shrink the JS and wasm we emit by default. See details in that previous discussion.

To get things started, I looked at one testcase - we should look at more, hence the testcase #1 in the title, this is just to get started. The testcase is a "pure computation" library,

#include <emscripten.h>

EMSCRIPTEN_KEEPALIVE
int add(int x, int y) {
  return x + y;
}

and I built it with -Os --closure 1 -g1 -s WASM=1, then counted lines in the JS. Starting point: 10K of wasm and 24K of JS when fully minified, or when built as I did with -g1 for convenience, it is 32K, in 1,143 lines. In more detail:

• 232 lines: String and array utilities, ccall, cwrap Less default runtime exports #5892 (need more)
• 132 lines: wasm glue. Clean up wasm glue #5859 Remove the asmGlobal if not using asm.js #5907 (may need more)
• 109 lines: ENVIRONMENT setup stuff.
• 102 lines: Calling main + the hooks around that. Don't emit code to call main if there is no main #5850 (need more)
• 88 lines: Runtime object. De-runtime-ification #5954
• 55 lines: getValue/setValue. do not export getValue and setValue by default #5839
• 55 lines: Syscalls.
• 55 lines: Export stuff from asm (all the Module.x = get the thing from asm.x etc).
• 44 lines: Stack trace support. ifdef demangle JS support code, include it only when needed #5857
• 44 lines: addOnPreRun, runDependency etc, startup ordering stuff.
• 35 lines: Memory and view creation.
• 34 lines: allocate()
• 27 lines: Math fallbacks (imul, clz, trunc). Remove legacy support for polyfilling Math.clz32, imul, trunc #5837
• 27 lines: Mem init file loading. Don't inclue mem init loading code when it is inside the wasm anyhow #5844
• 18 lines: invoke/dynCall stubs.

Also

• Meta-DCE Meta-DCE for JS+WASM #5919

If you want to work on one of these, open an issue or a PR, and we can add a link from here.