enhance `unused` (#3794)

1 files changed, 27 insertions, 18 deletions

diff --git a/lib/compress.js b/lib/compress.js
index d6f6a710..3aa9f0bc 100644
--- a/lib/compress.js
+++ b/lib/compress.js
@@ -4134,6 +4134,7 @@ merge(Compressor.prototype, {
                 // side effects, we can cascade the init. code
                 // into the next one, or next statement.
                 var side_effects = [];
+                var duplicated = 0;
                 node.definitions.forEach(function(def) {
                     if (def.value) def.value = def.value.transform(tt);
                     var sym = def.name.definition();
@@ -4142,24 +4143,17 @@ merge(Compressor.prototype, {
                             def.value = def.value.drop_side_effect_free(compressor);
                         }
                         var var_defs = var_defs_by_id.get(sym.id);
-                        if (var_defs.length > 1 && (!def.value || sym.orig.indexOf(def.name) > sym.eliminated)) {
-                            AST_Node.warn("Dropping duplicated definition of variable {name} [{file}:{line},{col}]", template(def.name));
-                            if (def.value) {
-                                var ref = make_node(AST_SymbolRef, def.name, def.name);
-                                sym.references.push(ref);
-                                var assign = make_node(AST_Assign, def, {
-                                    operator: "=",
-                                    left: ref,
-                                    right: def.value
-                                });
-                                if (fixed_ids[sym.id] === def) {
-                                    fixed_ids[sym.id] = assign;
-                                }
-                                side_effects.push(assign.transform(tt));
+                        if (var_defs.length > 1) {
+                            if (!def.value) {
+                                AST_Node.warn("Dropping duplicated declaration of variable {name} [{file}:{line},{col}]", template(def.name));
+                                remove(var_defs, def);
+                                sym.eliminated++;
+                                return;
+                            }
+                            if (sym.orig.indexOf(def.name) > sym.eliminated) {
+                                remove(var_defs, def);
+                                duplicated++;
                             }
-                            remove(var_defs, def);
-                            sym.eliminated++;
-                            return;
                         }
                         if (!def.value) {
                             head.push(def);
@@ -4220,7 +4214,22 @@ merge(Compressor.prototype, {
                         return !def || fn.name && def === fn.name.definition();
                     }
                 });
-                if (head.length > 0 || tail.length > 0) {
+                if (head.length == 0 && tail.length == duplicated) {
+                    [].unshift.apply(side_effects, tail.map(function(def) {
+                        AST_Node.warn("Dropping duplicated definition of variable {name} [{file}:{line},{col}]", template(def.name));
+                        var sym = def.name.definition();
+                        var ref = make_node(AST_SymbolRef, def.name, def.name);
+                        sym.references.push(ref);
+                        var assign = make_node(AST_Assign, def, {
+                            operator: "=",
+                            left: ref,
+                            right: def.value
+                        });
+                        if (fixed_ids[sym.id] === def) fixed_ids[sym.id] = assign;
+                        sym.eliminated++;
+                        return assign.transform(tt);
+                    }));
+                } else if (head.length > 0 || tail.length > 0) {
                     node.definitions = head.concat(tail);
                     body.push(node);
                 }