Emscripten and spec disagree about mutability of foreign imports.

[cscott]

The spec says:

A foreign import is of one of the following three forms:

var x:Identifier = foreign:Identifier.y:Identifier; var x:Identifier = foreign:Identifier.y:Identifier|0; var x:Identifier = +foreign:Identifier.y:Identifier;

The variable foreign must match the second parameter of the module declaration. The global variable x is stored in the global environment with type imm Function for the first form, imm int for the second, and imm double for the third.

The spec should probably read "mut int for the second and mut double for the third", since emscripten generates the following code (this is from https://github.com/dvander/arewefastyet/blob/9de7037324e0b5b155b761225f26f94fff5c76f5/benchmarks/asmjs-apps/box2d.js):

    var i = env.STACKTOP | 0;
    function a5(a) {
        a = a | 0;
        var b = 0;
        b = i;
        i = i + a | 0;
        i = i + 3 >> 2 << 2;
        return b | 0
    }

[ghost]

This has been fixed in Section 5.5.