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enhance reduce_vars (#1814)

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- allow immediate assignment after declaration of variable
- relax modification rule for immutable value
- fix order of visit for TreeWalker
- remove extraneous code
This commit is contained in:
Alex Lam S.L
2017-04-17 01:36:50 +08:00
committed by GitHub
parent 44dfa5a318
commit 1a498db2d3
3 changed files with 193 additions and 33 deletions
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74
lib/compress.js
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@@ -119,7 +119,7 @@ merge(Compressor.prototype, {
option: function(key) { return this.options[key] },
compress: function(node) {
if (this.option("expression")) {
node = node.process_expression(true);
node.process_expression(true);
}
var passes = +this.options.passes || 1;
for (var pass = 0; pass < passes && pass < 3; ++pass) {
@@ -128,7 +128,7 @@ merge(Compressor.prototype, {
node = node.transform(this);
}
if (this.option("expression")) {
node = node.process_expression(false);
node.process_expression(false);
}
return node;
},
@@ -200,7 +200,7 @@ merge(Compressor.prototype, {
return this.TYPE == node.TYPE && this.print_to_string() == node.print_to_string();
});
AST_Node.DEFMETHOD("process_expression", function(insert, compressor) {
AST_Scope.DEFMETHOD("process_expression", function(insert, compressor) {
var self = this;
var tt = new TreeTransformer(function(node) {
if (insert && node instanceof AST_SimpleStatement) {
@@ -244,10 +244,10 @@ merge(Compressor.prototype, {
}
return node;
});
return self.transform(tt);
self.transform(tt);
});
AST_Node.DEFMETHOD("reset_opt_flags", function(compressor, rescan){
AST_Node.DEFMETHOD("reset_opt_flags", function(compressor, rescan) {
var reduce_vars = rescan && compressor.option("reduce_vars");
var toplevel = compressor.option("toplevel");
var safe_ids = Object.create(null);
@@ -258,7 +258,7 @@ merge(Compressor.prototype, {
d.fixed = false;
}
});
var tw = new TreeWalker(function(node, descend){
var tw = new TreeWalker(function(node, descend) {
node._squeezed = false;
node._optimized = false;
if (reduce_vars) {
@@ -268,7 +268,7 @@ merge(Compressor.prototype, {
var d = node.definition();
d.references.push(node);
if (d.fixed === undefined || !is_safe(d)
|| is_modified(node, 0, node.fixed_value() instanceof AST_Lambda)) {
|| is_modified(node, 0, is_immutable(node.fixed_value()))) {
d.fixed = false;
}
}
@@ -293,6 +293,20 @@ merge(Compressor.prototype, {
d.fixed = false;
}
}
if (node instanceof AST_Assign
&& node.operator == "="
&& node.left instanceof AST_SymbolRef) {
var d = node.left.definition();
if (HOP(safe_ids, d.id) && d.fixed == null) {
d.fixed = function() {
return node.right;
};
mark(d, false);
node.right.walk(tw);
mark(d, true);
return true;
}
}
if (node instanceof AST_Defun) {
var d = node.name.definition();
if (!toplevel && d.global || is_safe(d)) {
@@ -309,21 +323,24 @@ merge(Compressor.prototype, {
}
var iife;
if (node instanceof AST_Function
&& !node.name
&& (iife = tw.parent()) instanceof AST_Call
&& iife.expression === node) {
// Virtually turn IIFE parameters into variable definitions:
// (function(a,b) {...})(c,d) => (function() {var a=c,b=d; ...})()
// So existing transformation rules can work on them.
node.argnames.forEach(function(arg, i) {
var d = arg.definition();
d.fixed = function() {
return iife.args[i] || make_node(AST_Undefined, iife);
};
mark(d, true);
});
if (node.name) {
node.name.definition().fixed = node;
} else {
// Virtually turn IIFE parameters into variable definitions:
// (function(a,b) {...})(c,d) => (function() {var a=c,b=d; ...})()
// So existing transformation rules can work on them.
node.argnames.forEach(function(arg, i) {
var d = arg.definition();
d.fixed = function() {
return iife.args[i] || make_node(AST_Undefined, iife);
};
mark(d, true);
});
}
}
if (node instanceof AST_If || node instanceof AST_DWLoop) {
if (node instanceof AST_If) {
node.condition.walk(tw);
push();
node.body.walk(tw);
@@ -335,6 +352,13 @@ merge(Compressor.prototype, {
}
return true;
}
if (node instanceof AST_DWLoop) {
push();
node.condition.walk(tw);
node.body.walk(tw);
pop();
return true;
}
if (node instanceof AST_LabeledStatement) {
push();
node.body.walk(tw);
@@ -401,13 +425,17 @@ merge(Compressor.prototype, {
def.should_replace = undefined;
}
function is_modified(node, level, func) {
function is_immutable(value) {
return value && value.is_constant() || value instanceof AST_Lambda;
}
function is_modified(node, level, immutable) {
var parent = tw.parent(level);
if (is_lhs(node, parent)
|| !func && parent instanceof AST_Call && parent.expression === node) {
|| !immutable && parent instanceof AST_Call && parent.expression === node) {
return true;
} else if (parent instanceof AST_PropAccess && parent.expression === node) {
return !func && is_modified(parent, level + 1);
return !immutable && is_modified(parent, level + 1);
}
}
});
@@ -2167,7 +2195,7 @@ merge(Compressor.prototype, {
if (this.expression instanceof AST_Function
&& (!this.expression.name || !this.expression.name.definition().references.length)) {
var node = this.clone();
node.expression = node.expression.process_expression(false, compressor);
node.expression.process_expression(false, compressor);
return node;
}
return this;