facebookarchive/prepack
View on GitHubEliminate unnecessary object allocations for residual functions
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#495 opened on May 2, 2017
enhancementhelp wantedserializer
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Description
Prepacking
function() {
function f() {
let obj = { f: 42 };
return function() { return obj.f; }
}
g = f();
})();
currently yields the following:
(function () {
var _1 = {
f: 42
};
function _0() {
return _1.f;
}
g = _0;
})();
The object allocation for _1 is silly. #494 suggests delaying the allocation, but in this example, it could be completely eliminated. Prepack could generate the following code:
(function () {
let _1_f = 42;
function _0() {
return _1_f;
}
g = _0;
})();
Or even better:
(function () {
function _0() {
return 42;
}
g = _0;
})();
If instead of 42 the field obj.f may either hold an object reference or may be mutated by the residual code, then another variable similar to _1 would be needed.