Wasm2JS redundant x + 0 operations

[juj]

Building juj/wasm_webgpu@4c2600b clear_screen sample for testing WebGPU on Wasm2JS, I notice the following kind of statements appear:

  $3 = (.6666666666666666 - $2) * 6 + 0;
   $3 = $2 * 6 + 0;
  $3 = (.6666666666666666 - $2) * 6 + 0;
   $3 = $2 * 6 + 0;
  $3 = (.6666666666666666 - $0) * 6 + 0;
   $3 = $0 * 6 + 0;

It seems that it would be feasible to optimize away those + 0 additions.

[juj]

Looks like Closure does not optimize these away:

  d = (.6666666666666666 - c) * 6 + 0;
   d = a * 6 + 0;

[kripken]

I think there are issues with negative zero that prevent it:

$ node
Welcome to Node.js v15.6.0.
Type ".help" for more information.
> -0.0 + 0
0
> -0.0 + -0.0
-0
> 0 + -0.0
0

It is valid to remove + -0.0 but not + 0.0, and binaryen does that. However, I think in fastMath we could do both, but we don't atm:

https://github.com/WebAssembly/binaryen/blob/89b811699b2db0c0e2ad744a1240f6283f8eed86/src/passes/OptimizeInstructions.cpp#L1826-L1833

[stale]

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