update SymbolDef.orig after drop_unused()

lib/compress.js

@@ -2075,6 +2075,7 @@ merge(Compressor.prototype, {
                                 if (var_defs.length > 1 && !def.value) {
                                     compressor.warn("Dropping duplicated definition of variable {name} [{file}:{line},{col}]", template(def.name));
                                     var_defs.splice(var_defs.indexOf(def), 1);
+                                    sym.orig.splice(sym.orig.indexOf(def.name), 1);
                                     return;
                                 }
                             }
@@ -2107,6 +2108,7 @@ merge(Compressor.prototype, {
                             } else {
                                 compressor[def.name.unreferenced() ? "warn" : "info"]("Dropping unused variable {name} [{file}:{line},{col}]", template(def.name));
                             }
+                            sym.orig.splice(sym.orig.indexOf(def.name), 1);
                         }
                     });
                     if (head.length == 0 && tail.length == 1 && tail[0].name instanceof AST_SymbolVar) {
@@ -2115,6 +2117,8 @@ merge(Compressor.prototype, {
                             var def = tail.pop();
                             compressor.warn("Converting duplicated definition of variable {name} to assignment [{file}:{line},{col}]", template(def.name));
                             var_defs.splice(var_defs.indexOf(def), 1);
+                            var orig = def.name.definition().orig;
+                            orig.splice(orig.indexOf(def.name), 1);
                             side_effects.unshift(make_node(AST_Assign, def, {
                                 operator: "=",
                                 left: make_node(AST_SymbolRef, def.name, def.name),

test/compress/collapse_vars.js

@@ -2077,3 +2077,40 @@ toplevel_single_reference: {
             b(a = b);
     }
 }
+
+unused_orig: {
+    options = {
+        collapse_vars: true,
+        passes: 2,
+        reduce_vars: true,
+        unused: true,
+    }
+    input: {
+        var a = 1;
+        console.log(function(b) {
+            var a;
+            var c = b;
+            for (var d in c) {
+                var a = c[0];
+                return --b + a;
+            }
+            try {
+            } catch (e) {
+                --b + a;
+            }
+            a && a.NaN;
+        }([2]), a);
+    }
+    expect: {
+        var a = 1;
+        console.log(function(b) {
+            var c = b;
+            for (var d in c) {
+                var a = c[0];
+                return --b + a;
+            }
+            a && a.NaN;
+        }([2]), a);
+    }
+    expect_stdout: "3 1"
+}