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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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12
lib/ast.js
View File

@@ -182,21 +182,13 @@ var AST_BlockStatement = DEFNODE("BlockStatement", null, {
}, AST_Block);
var AST_EmptyStatement = DEFNODE("EmptyStatement", null, {
$documentation: "The empty statement (empty block or simply a semicolon)",
_walk: function(visitor) {
return visitor._visit(this);
}
$documentation: "The empty statement (empty block or simply a semicolon)"
}, AST_Statement);
var AST_StatementWithBody = DEFNODE("StatementWithBody", "body", {
$documentation: "Base class for all statements that contain one nested body: `For`, `ForIn`, `Do`, `While`, `With`",
$propdoc: {
body: "[AST_Statement] the body; this should always be present, even if it's an AST_EmptyStatement"
},
_walk: function(visitor) {
return visitor._visit(this, function(){
this.body._walk(visitor);
});
}
}, AST_Statement);
@@ -551,11 +543,11 @@ var AST_Call = DEFNODE("Call", "expression args", {
},
_walk: function(visitor) {
return visitor._visit(this, function(){
this.expression._walk(visitor);
var args = this.args;
for (var i = 0, len = args.length; i < len; i++) {
args[i]._walk(visitor);
}
this.expression._walk(visitor);
});
}
});

74
lib/compress.js
View File

@@ -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;

140
test/compress/reduce_vars.js
View File

@@ -1996,6 +1996,146 @@ catch_var: {
expect_stdout: "true"
}
var_assign_1: {
options = {
evaluate: true,
reduce_vars: true,
sequences: true,
side_effects: true,
unused: true,
}
input: {
!function() {
var a;
a = 2;
console.log(a);
}();
}
expect: {
!function() {
console.log(2);
}();
}
expect_stdout: "2"
}
var_assign_2: {
options = {
evaluate: true,
reduce_vars: true,
sequences: true,
side_effects: true,
unused: true,
}
input: {
!function() {
var a;
if (a = 2) console.log(a);
}();
}
expect: {
!function() {
if (2) console.log(2);
}();
}
expect_stdout: "2"
}
var_assign_3: {
options = {
evaluate: true,
reduce_vars: true,
sequences: true,
side_effects: true,
unused: true,
}
input: {
!function() {
var a;
while (a = 2);
console.log(a);
}();
}
expect: {
!function() {
var a;
while (a = 2);
console.log(a);
}();
}
}
var_assign_4: {
options = {
evaluate: true,
reduce_vars: true,
sequences: true,
side_effects: true,
unused: true,
}
input: {
!function a() {
a = 2;
console.log(a);
}();
}
expect: {
!function a() {
a = 2,
console.log(a);
}();
}
}
var_assign_5: {
options = {
evaluate: true,
reduce_vars: true,
sequences: true,
side_effects: true,
unused: true,
}
input: {
!function() {
var a;
!function(b) {
a = 2;
console.log(a, b);
}(a);
}();
}
expect: {
!function() {
var a;
!function(b) {
a = 2,
console.log(a, b);
}(a);
}();
}
expect_stdout: "2 undefined"
}
immutable: {
options = {
evaluate: true,
reduce_vars: true,
unused: true,
}
input: {
!function() {
var a = "test";
console.log(a.indexOf("e"));
}();
}
expect: {
!function() {
console.log("test".indexOf("e"));
}();
}
expect_stdout: "1"
}
issue_1814_1: {
options = {
evaluate: true,