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compress duplicated variable definitions (#1817)

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These are surprisingly common, as people reuse the same variable name within loops or switch branches.
This commit is contained in:
Alex Lam S.L
2017-04-17 17:11:29 +08:00
committed by GitHub
parent 71a8d0d236
commit 4ffb6fce76
4 changed files with 73 additions and 11 deletions
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52
lib/compress.js
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@@ -1813,6 +1813,7 @@ merge(Compressor.prototype, {
}
});
}
var var_defs_by_id = new Dictionary();
var initializations = new Dictionary();
// pass 1: find out which symbols are directly used in
// this scope (not in nested scopes).
@@ -1832,8 +1833,11 @@ merge(Compressor.prototype, {
}
if (node instanceof AST_Definitions && scope === self) {
node.definitions.forEach(function(def){
var node_def = def.name.definition();
if (def.name instanceof AST_SymbolVar) {
var_defs_by_id.add(node_def.id, def);
}
if (!drop_vars) {
var node_def = def.name.definition();
if (!(node_def.id in in_use_ids)) {
in_use_ids[node_def.id] = true;
in_use.push(node_def);
@@ -1943,19 +1947,29 @@ merge(Compressor.prototype, {
}
if (drop_vars && node instanceof AST_Definitions && !(tt.parent() instanceof AST_ForIn)) {
var def = node.definitions.filter(function(def){
if (def.value) def.value = def.value.transform(tt);
var sym = def.name.definition();
if (sym.id in in_use_ids) return true;
if (sym.orig[0] instanceof AST_SymbolCatch) {
def.value = def.value && def.value.drop_side_effect_free(compressor);
return true;
}
var w = {
name : def.name.name,
file : def.name.start.file,
line : def.name.start.line,
col : def.name.start.col
};
if (def.value) def.value = def.value.transform(tt);
var sym = def.name.definition();
if (sym.id in in_use_ids) {
if (def.name instanceof AST_SymbolVar) {
var var_defs = var_defs_by_id.get(sym.id);
if (var_defs.length > 1 && !def.value) {
compressor.warn("Dropping duplicated definition of variable {name} [{file}:{line},{col}]", w);
var_defs.splice(var_defs.indexOf(def), 1);
return false;
}
}
return true;
}
if (sym.orig[0] instanceof AST_SymbolCatch) {
def.value = def.value && def.value.drop_side_effect_free(compressor);
return true;
}
if (def.value && (def._unused_side_effects = def.value.drop_side_effect_free(compressor))) {
compressor.warn("Side effects in initialization of unused variable {name} [{file}:{line},{col}]", w);
return true;
@@ -1963,6 +1977,28 @@ merge(Compressor.prototype, {
compressor[def.name.unreferenced() ? "warn" : "info"]("Dropping unused variable {name} [{file}:{line},{col}]", w);
return false;
});
if (def.length == 1
&& def[0].value
&& !def[0]._unused_side_effects
&& def[0].name instanceof AST_SymbolVar) {
var var_defs = var_defs_by_id.get(def[0].name.definition().id);
if (var_defs.length > 1) {
compressor.warn("Converting duplicated definition of variable {name} to assignment [{file}:{line},{col}]", {
name : def[0].name.name,
file : def[0].name.start.file,
line : def[0].name.start.line,
col : def[0].name.start.col
});
var_defs.splice(var_defs.indexOf(def[0]), 1);
return make_node(AST_SimpleStatement, node, {
body: make_node(AST_Assign, def[0], {
operator: "=",
left: make_node(AST_SymbolRef, def[0].name, def[0].name),
right: def[0].value
})
});
}
}
// place uninitialized names at the start
def = mergeSort(def, function(a, b){
if (!a.value && b.value) return -1;