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improve pure_getters (#1786)

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- property access to `null` & `undefined` always has side effects
- utilise `reduce_vars` to determine safe property access
- may-be cases treated as side effects unless `unsafe`
This commit is contained in:
Alex Lam S.L
2017-04-06 11:18:59 +08:00
committed by GitHub
parent ff289b90a9
commit 06cdb74279
4 changed files with 113 additions and 8 deletions
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34
lib/compress.js
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@@ -1160,6 +1160,26 @@ merge(Compressor.prototype, {
&& !node.expression.has_side_effects(compressor);
}
(function(def) {
def(AST_Node, return_false);
def(AST_Null, return_true);
def(AST_Undefined, return_true);
def(AST_UnaryPrefix, function() {
return this.operator == "void";
});
def(AST_PropAccess, function(compressor) {
return !compressor.option("unsafe");
});
def(AST_SymbolRef, function(compressor) {
if (this.is_undefined) return true;
if (compressor.option("unsafe")) return false;
var fixed = this.fixed_value();
return !fixed || fixed.may_eq_null(compressor);
});
})(function(node, func) {
node.DEFMETHOD("may_eq_null", func);
});
/* -----[ boolean/negation helpers ]----- */
// methods to determine whether an expression has a boolean result type
@@ -1688,7 +1708,7 @@ merge(Compressor.prototype, {
|| this.expression.has_side_effects(compressor);
});
def(AST_SymbolRef, function(compressor){
return this.global() && this.undeclared();
return this.undeclared();
});
def(AST_Object, function(compressor){
return any(this.properties, compressor);
@@ -1701,16 +1721,15 @@ merge(Compressor.prototype, {
});
def(AST_Dot, function(compressor){
if (!compressor.option("pure_getters")) return true;
return this.expression.has_side_effects(compressor);
return this.expression.may_eq_null(compressor)
|| this.expression.has_side_effects(compressor);
});
def(AST_Sub, function(compressor){
if (!compressor.option("pure_getters")) return true;
return this.expression.has_side_effects(compressor)
return this.expression.may_eq_null(compressor)
|| this.expression.has_side_effects(compressor)
|| this.property.has_side_effects(compressor);
});
def(AST_PropAccess, function(compressor){
return !compressor.option("pure_getters");
});
def(AST_Seq, function(compressor){
return this.car.has_side_effects(compressor)
|| this.cdr.has_side_effects(compressor);
@@ -2275,10 +2294,12 @@ merge(Compressor.prototype, {
});
def(AST_Dot, function(compressor, first_in_statement){
if (!compressor.option("pure_getters")) return this;
if (this.expression.may_eq_null(compressor)) return this;
return this.expression.drop_side_effect_free(compressor, first_in_statement);
});
def(AST_Sub, function(compressor, first_in_statement){
if (!compressor.option("pure_getters")) return this;
if (this.expression.may_eq_null(compressor)) return this;
var expression = this.expression.drop_side_effect_free(compressor, first_in_statement);
if (!expression) return this.property.drop_side_effect_free(compressor, first_in_statement);
var property = this.property.drop_side_effect_free(compressor);
@@ -3509,7 +3530,6 @@ merge(Compressor.prototype, {
// testing against !self.scope.uses_with first is an optimization
if (compressor.option("screw_ie8")
&& self.undeclared()
&& !isLHS(self, compressor.parent())
&& (!self.scope.uses_with || !compressor.find_parent(AST_With))) {
switch (self.name) {
case "undefined":