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implement optimization: (x = 2 * x) ---> (x *= 2)

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kzc
2016-08-26 18:47:25 -04:00
parent 1a78bbcd23
commit 0bd8053524
3 changed files with 258 additions and 10 deletions
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26
lib/compress.js
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@@ -2655,16 +2655,26 @@ merge(Compressor.prototype, {
});
var ASSIGN_OPS = [ '+', '-', '/', '*', '%', '>>', '<<', '>>>', '|', '^', '&' ];
var ASSIGN_OPS_COMMUTATIVE = [ '*', '|', '^', '&' ];
OPT(AST_Assign, function(self, compressor){
self = self.lift_sequences(compressor);
if (self.operator == "="
&& self.left instanceof AST_SymbolRef
&& self.right instanceof AST_Binary
&& self.right.left instanceof AST_SymbolRef
&& self.right.left.name == self.left.name
&& member(self.right.operator, ASSIGN_OPS)) {
self.operator = self.right.operator + "=";
self.right = self.right.right;
if (self.operator == "=" && self.left instanceof AST_SymbolRef && self.right instanceof AST_Binary) {
// x = expr1 OP expr2
if (self.right.left instanceof AST_SymbolRef
&& self.right.left.name == self.left.name
&& member(self.right.operator, ASSIGN_OPS)) {
// x = x - 2 ---> x -= 2
self.operator = self.right.operator + "=";
self.right = self.right.right;
}
else if (self.right.right instanceof AST_SymbolRef
&& self.right.right.name == self.left.name
&& member(self.right.operator, ASSIGN_OPS_COMMUTATIVE)
&& !self.right.left.has_side_effects(compressor)) {
// x = 2 & x ---> x &= 2
self.operator = self.right.operator + "=";
self.right = self.right.left;
}
}
return self;
});