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drop unused compound assignments (#2230)

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fixes #2226
This commit is contained in:
Alex Lam S.L
2017-07-14 00:39:34 +08:00
committed by GitHub
parent 458e3e15f0
commit 5229cb2b1b
3 changed files with 118 additions and 21 deletions
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45
lib/compress.js
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@@ -790,6 +790,7 @@ merge(Compressor.prototype, {
right: candidate.value
});
}
candidate.write_only = false;
return candidate;
}
// These node types have child nodes that execute sequentially,
@@ -2177,7 +2178,12 @@ merge(Compressor.prototype, {
var drop_funcs = !(self instanceof AST_Toplevel) || compressor.toplevel.funcs;
var drop_vars = !(self instanceof AST_Toplevel) || compressor.toplevel.vars;
if (!drop_funcs && !drop_vars) return;
var assign_as_unused = !/keep_assign/.test(compressor.option("unused"));
var assign_as_unused = /keep_assign/.test(compressor.option("unused")) ? return_false : function(node) {
if (node instanceof AST_Assign && (node.write_only || node.operator == "=")) {
return node.left;
}
if (node instanceof AST_Unary && node.write_only) return node.expression;
};
var in_use = [];
var in_use_ids = Object.create(null); // avoid expensive linear scans of in_use
if (self instanceof AST_Toplevel && compressor.top_retain) {
@@ -2227,12 +2233,8 @@ merge(Compressor.prototype, {
});
return true;
}
if (assign_as_unused
&& node instanceof AST_Assign
&& node.operator == "="
&& node.left instanceof AST_SymbolRef
&& scope === self) {
node.right.walk(tw);
if (assign_as_unused(node) instanceof AST_SymbolRef && scope === self) {
if (node instanceof AST_Assign) node.right.walk(tw);
return true;
}
if (node instanceof AST_SymbolRef) {
@@ -2396,14 +2398,17 @@ merge(Compressor.prototype, {
});
}
}
if (drop_vars && assign_as_unused
&& node instanceof AST_Assign
&& node.operator == "="
&& node.left instanceof AST_SymbolRef) {
var def = node.left.definition();
if (!(def.id in in_use_ids)
if (drop_vars) {
var def = assign_as_unused(node);
if (def instanceof AST_SymbolRef
&& !((def = def.definition()).id in in_use_ids)
&& self.variables.get(def.name) === def) {
return maintain_this_binding(tt.parent(), node, node.right.transform(tt));
if (node instanceof AST_Assign) {
return maintain_this_binding(tt.parent(), node, node.right.transform(tt));
}
return make_node(AST_Number, node, {
value: 0
});
}
}
// certain combination of unused name + side effect leads to:
@@ -2642,7 +2647,10 @@ merge(Compressor.prototype, {
return make_sequence(this, [ left, right ]);
}
});
def(AST_Assign, return_this);
def(AST_Assign, function(compressor){
this.write_only = !this.left.has_side_effects(compressor);
return this;
});
def(AST_Conditional, function(compressor){
var consequent = this.consequent.drop_side_effect_free(compressor);
var alternative = this.alternative.drop_side_effect_free(compressor);
@@ -2663,7 +2671,10 @@ merge(Compressor.prototype, {
return node;
});
def(AST_Unary, function(compressor, first_in_statement){
if (unary_side_effects(this.operator)) return this;
if (unary_side_effects(this.operator)) {
this.write_only = !this.expression.has_side_effects(compressor);
return this;
}
if (this.operator == "typeof" && this.expression instanceof AST_SymbolRef) return null;
var expression = this.expression.drop_side_effect_free(compressor, first_in_statement);
if (first_in_statement
@@ -3485,7 +3496,7 @@ merge(Compressor.prototype, {
operator: car.operator,
expression: left
});
}
} else car.write_only = false;
if (parent) {
parent[field] = car;
expressions[i] = expressions[j];