dart2js: readability and code size: || and && code generates unnecessary temporaries #7475
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Changed the title to: "dart2js: readability and code size: || and && code generates unnecessary temporaries". |
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Added this to the M3 milestone. |
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Added TriageForM5 label. |
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Removed this from the M5 milestone. |
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Removed this from the Later milestone. |
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Removed Oldschool-Milestone-Later label. |
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This code is amazingly similar today to what @rakudrama reported in 2012, when compiling with import 'dart:html';
void main() async {
var request = await HttpRequest.request('f.json');
request.onReadyStateChange.listen((e) {
if (request.readyState == HttpRequest.DONE &&
(request.status == 200 || request.status == 0)) {
onSuccess(request);
}
});
}
void onSuccess(HttpRequest req) => print(req);compiled with -O1: F.main_closure.prototype = {
call$1: function(e) {
var t2,
t1 = this.request;
if (t1.readyState === 4) {
t2 = t1.status;
t2 = t2 === 200 || t2 === 0;
} else
t2 = false;
if (t2)
H.printString(H.S(t1));
},
$signature: 17
};Compiled with -O4 is about the same, minified: F.bf.prototype={
$1:function(a){var u,t=this.a
if(t.readyState===4){u=t.status
u=u===200||u===0}else u=!1
if(u)H.cS(H.b(t))}}; |
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This closure:
request.on.readyStateChange.add((e) {
if (request.readyState == HttpRequest.DONE &&
(request.status == 200 || request.status == 0)) {
onSuccess(request);
}
});
compiles to:
$$._HttpRequestUtils_get_anon = {"":"Closure;request_0,onSuccess_1",
call$1: function(e) {
var t1, t2;
t1 = this.request_0;
if ($.eqB(t1.get$readyState(), 4))
t2 = $.eqB(t1.get$status(), 200) || $.eqB(t1.get$status(), 0);
else
t2 = false;
if (t2)
this.onSuccess_1.call$1(t1);
}
};
t2 is unnecessary and, if removed, the code is smaller and closer to the original Dart code:
$$._HttpRequestUtils_get_anon = {"":"Closure;request_0,onSuccess_1",
call$1: function(e) {
var t1;
t1 = this.request_0;
if ($.eqB(t1.get$readyState(), 4))
if ($.eqB(t1.get$status(), 200) || $.eqB(t1.get$status(), 0))
this.onSuccess_1.call$1(t1);
}
};
The problem with the generated code is that one branch of the if-the-else ensures that the if-then is not taken.
Instead, the body of the if-then should be generated in the other branch of the if-then-else.
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