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optimization for if/break as first statement in a loop body

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for(...; x; ...) if (y) break; → for(...; x&&!y; ...);

similarly for `while` and some combinations (i.e. the `break` appears in the
`else` clause, etc.)
This commit is contained in:
Mihai Bazon
2012-11-07 18:57:51 +02:00
parent 5a7e54cf72
commit 1a5fd3e052
2 changed files with 171 additions and 1 deletions
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49
lib/compress.js
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@@ -1118,11 +1118,57 @@ merge(Compressor.prototype, {
return self;
});
function if_break_in_loop(self, compressor) {
function drop_it(rest) {
rest = as_statement_array(rest);
if (self.body instanceof AST_BlockStatement) {
self.body = self.body.clone();
self.body.body = rest.concat(self.body.body.slice(1));
self.body = self.body.transform(compressor);
} else {
self.body = make_node(AST_BlockStatement, self.body, {
body: rest
}).transform(compressor);
}
if_break_in_loop(self, compressor);
}
var first = self.body instanceof AST_BlockStatement ? self.body.body[0] : self.body;
if (first instanceof AST_If) {
if (first.body instanceof AST_Break
&& compressor.loopcontrol_target(first.body.label) === self) {
if (self.condition) {
self.condition = make_node(AST_Binary, self.condition, {
left: self.condition,
operator: "&&",
right: first.condition.negate(compressor),
});
} else {
self.condition = first.condition.negate(compressor);
}
drop_it(first.alternative);
}
else if (first.alternative instanceof AST_Break
&& compressor.loopcontrol_target(first.alternative.label) === self) {
if (self.condition) {
self.condition = make_node(AST_Binary, self.condition, {
left: self.condition,
operator: "&&",
right: first.condition,
});
} else {
self.condition = first.condition;
}
drop_it(first.body);
}
}
};
OPT(AST_While, function(self, compressor) {
if (!compressor.option("loops")) return self;
self = AST_DWLoop.prototype.optimize.call(self, compressor);
if (self instanceof AST_While) {
self = make_node(AST_For, self, self);
if_break_in_loop(self, compressor);
self = make_node(AST_For, self, self).transform(compressor);
}
return self;
});
@@ -1151,6 +1197,7 @@ merge(Compressor.prototype, {
}
}
}
if_break_in_loop(self, compressor);
return self;
});