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support safe reassignments in reduce_vars (#1823)

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`var a=1;a=2;x(a)` => `x(2)`

fix pre-existing issues
- reference counting on assignment
- walking of anonymous functions
- chained assignment
This commit is contained in:
Alex Lam S.L
2017-04-18 13:38:42 +08:00
committed by GitHub
parent d1aa09c5c7
commit 5d9f1da3ab
3 changed files with 145 additions and 30 deletions
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51
lib/compress.js
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@@ -267,7 +267,7 @@ merge(Compressor.prototype, {
if (node instanceof AST_SymbolRef) {
var d = node.definition();
d.references.push(node);
if (d.fixed === undefined || !is_safe(d)
if (d.fixed === undefined || !safe_to_read(d)
|| is_modified(node, 0, is_immutable(node.fixed_value()))) {
d.fixed = false;
}
@@ -277,7 +277,7 @@ merge(Compressor.prototype, {
}
if (node instanceof AST_VarDef) {
var d = node.name.definition();
if (d.fixed == null) {
if (d.fixed === undefined || safe_to_assign(d, node.value)) {
if (node.value) {
d.fixed = function() {
return node.value;
@@ -297,7 +297,8 @@ merge(Compressor.prototype, {
&& node.operator == "="
&& node.left instanceof AST_SymbolRef) {
var d = node.left.definition();
if (HOP(safe_ids, d.id) && d.fixed == null) {
if (safe_to_assign(d, node.right)) {
d.references.push(node.left);
d.fixed = function() {
return node.right;
};
@@ -309,7 +310,7 @@ merge(Compressor.prototype, {
}
if (node instanceof AST_Defun) {
var d = node.name.definition();
if (!toplevel && d.global || is_safe(d)) {
if (!toplevel && d.global || safe_to_read(d)) {
d.fixed = false;
} else {
d.fixed = node;
@@ -321,13 +322,12 @@ merge(Compressor.prototype, {
safe_ids = save_ids;
return true;
}
var iife;
if (node instanceof AST_Function
&& (iife = tw.parent()) instanceof AST_Call
&& iife.expression === node) {
if (node.name) {
node.name.definition().fixed = node;
} else {
if (node instanceof AST_Function) {
push();
var iife;
if (!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.
@@ -339,6 +339,9 @@ merge(Compressor.prototype, {
mark(d, true);
});
}
descend();
pop();
return true;
}
if (node instanceof AST_Binary
&& (node.operator == "&&" || node.operator == "||")) {
@@ -385,11 +388,19 @@ merge(Compressor.prototype, {
}
if (node instanceof AST_For) {
if (node.init) node.init.walk(tw);
if (node.condition) {
push();
node.condition.walk(tw);
pop();
}
push();
if (node.condition) node.condition.walk(tw);
node.body.walk(tw);
if (node.step) node.step.walk(tw);
pop();
if (node.step) {
push();
node.step.walk(tw);
pop();
}
return true;
}
if (node instanceof AST_ForIn) {
@@ -426,7 +437,7 @@ merge(Compressor.prototype, {
safe_ids[def.id] = safe;
}
function is_safe(def) {
function safe_to_read(def) {
if (safe_ids[def.id]) {
if (def.fixed == null) {
var orig = def.orig[0];
@@ -437,6 +448,18 @@ merge(Compressor.prototype, {
}
}
function safe_to_assign(def, value) {
if (!HOP(safe_ids, def.id)) return false;
if (!safe_to_read(def)) return false;
if (def.fixed === false) return false;
if (def.fixed != null && (!value || def.references.length > 0)) return false;
return !def.orig.some(function(sym) {
return sym instanceof AST_SymbolConst
|| sym instanceof AST_SymbolDefun
|| sym instanceof AST_SymbolLambda;
});
}
function push() {
safe_ids = Object.create(safe_ids);
}