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collapse assignment with adjacent subsequent usage (#1553)

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- consolidate `cascade` optimisations
- support ++/-- postfixes
- remove redundant optimisation identified in #1460

fixes #368
This commit is contained in:
Alex Lam S.L
2017-03-05 14:56:14 +08:00
committed by GitHub
parent b70591be1a
commit 35a849dc48
2 changed files with 68 additions and 16 deletions
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43
lib/compress.js
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@@ -607,10 +607,7 @@ merge(Compressor.prototype, {
return statements;
function is_lvalue(node, parent) {
return node instanceof AST_SymbolRef && (
(parent instanceof AST_Assign && node === parent.left)
|| (parent instanceof AST_Unary && parent.expression === node
&& (parent.operator == "++" || parent.operator == "--")));
return node instanceof AST_SymbolRef && isLHS(node, parent);
}
function replace_var(node, parent, is_constant) {
if (is_lvalue(node, parent)) return node;
@@ -1152,7 +1149,7 @@ merge(Compressor.prototype, {
});
function isLHS(node, parent) {
return parent instanceof AST_Unary && (parent.operator === "++" || parent.operator === "--")
return parent instanceof AST_Unary && (parent.operator == "++" || parent.operator == "--")
|| parent instanceof AST_Assign && parent.left === node;
}
@@ -2832,20 +2829,34 @@ merge(Compressor.prototype, {
self.car = self.car.drop_side_effect_free(compressor, first_in_statement(compressor));
if (!self.car) return maintain_this_binding(compressor.parent(), self, self.cdr);
if (compressor.option("cascade")) {
var left;
if (self.car instanceof AST_Assign
&& !self.car.left.has_side_effects(compressor)) {
if (self.car.left.equivalent_to(self.cdr)) {
return self.car;
}
if (self.cdr instanceof AST_Call
&& self.cdr.expression.equivalent_to(self.car.left)) {
self.cdr.expression = self.car;
return self.cdr;
}
left = self.car.left;
} else if (self.car instanceof AST_UnaryPostfix
&& (self.car.operator == "++" || self.car.operator == "--")) {
left = self.car.expression;
}
if (!self.car.has_side_effects(compressor)
&& self.car.equivalent_to(self.cdr)) {
return self.car;
if (left) {
var parent, field;
var cdr = self.cdr;
while (true) {
if (cdr.equivalent_to(left)) {
if (parent) {
parent[field] = self.car;
return self.cdr;
}
return self.car;
}
if (cdr instanceof AST_Binary && !(cdr instanceof AST_Assign)) {
field = cdr.left.is_constant() ? "right" : "left";
} else if (cdr instanceof AST_Call
|| cdr instanceof AST_Unary && cdr.operator != "++" && cdr.operator != "--") {
field = "expression";
} else break;
parent = cdr;
cdr = cdr[field];
}
}
}
if (is_undefined(self.cdr)) {