1 files changed, 10 insertions, 5 deletions

diff --git a/lib/compress.js b/lib/compress.js
index 767d5f9c..cf46e47f 100644
--- a/lib/compress.js
+++ b/lib/compress.js
@@ -771,6 +771,7 @@ merge(Compressor.prototype, {
                             var j = fn.argnames.indexOf(arg);
                             return (j < 0 ? value : iife.args[j]) || make_node(AST_Undefined, iife);
                         };
+                        d.fixed.assigns = [ arg ];
                     } else {
                         d.fixed = false;
                     }
@@ -4649,7 +4650,9 @@ merge(Compressor.prototype, {
                 return true; // don't go in nested scopes
             }
             if (node instanceof AST_SymbolFunarg && scope === self) {
-                var_defs_by_id.add(node.definition().id, node);
+                var node_def = node.definition();
+                var_defs_by_id.add(node_def.id, node);
+                assignments.add(node_def.id, node);
             }
             if (node instanceof AST_Definitions && scope === self) {
                 node.definitions.forEach(function(def) {
@@ -4790,7 +4793,8 @@ merge(Compressor.prototype, {
                     var trim = compressor.drop_fargs(node, parent);
                     for (var a = node.argnames, i = a.length; --i >= 0;) {
                         var sym = a[i];
-                        if (!(sym.definition().id in in_use_ids)) {
+                        var def = sym.definition();
+                        if (!(def.id in in_use_ids)) {
                             sym.__unused = true;
                             if (trim) {
                                 log(sym, "Dropping unused function argument {name}");
@@ -4798,6 +4802,7 @@ merge(Compressor.prototype, {
                             }
                         } else {
                             trim = false;
+                            if (indexOf_assign(def, sym) < 0) sym.__unused = null;
                         }
                     }
                     fns_with_marked_args.push(node);
@@ -6457,10 +6462,10 @@ merge(Compressor.prototype, {
         var side_effects = [];
         for (var i = 0; i < args.length; i++) {
             var trim = i >= fn.argnames.length;
-            if (trim || fn.argnames[i].__unused) {
+            if (trim || "__unused" in fn.argnames[i]) {
                 var node = args[i].drop_side_effect_free(compressor);
-                if (drop_fargs) {
-                    fn.argnames.splice(i, 1);
+                if (drop_fargs && (trim || fn.argnames[i].__unused)) {
+                    if (!trim) fn.argnames.splice(i, 1);
                     args.splice(i, 1);
                     if (node) side_effects.push(node);
                     i--;