fix corner case in reduce_vars (#5778)

fixes #5777

lib/compress.js

@@ -624,15 +624,9 @@ Compressor.prototype.compress = function(node) {
         }
 
         function pop_scope(tw, scope) {
-            var fn_defs = scope.fn_defs;
-            var tangled = scope.may_call_this === return_true ? fn_defs : fn_defs.filter(function(fn) {
-                if (fn.safe_ids === false) return true;
-                fn.safe_ids = tw.safe_ids;
-                walk_fn_def(tw, fn);
-                return false;
-            });
             pop(tw);
-            tangled.forEach(function(fn) {
+            var fn_defs = scope.fn_defs;
+            fn_defs.forEach(function(fn) {
                 fn.safe_ids = tw.safe_ids;
                 walk_fn_def(tw, fn);
             });

test/compress/reduce_vars.js

@@ -8148,3 +8148,77 @@ issue_5730_3: {
     }
     expect_stdout: "PASS"
 }
+
+issue_5777_1: {
+    options = {
+        reduce_vars: true,
+        unused: true,
+    }
+    input: {
+        function f() {
+            (function(a) {
+                function g() {
+                    h();
+                }
+                g();
+                a = function() {};
+                function h() {
+                    console.log(a);
+                }
+            })("PASS");
+        }
+        f();
+    }
+    expect: {
+        function f() {
+            (function(a) {
+                (function() {
+                    h();
+                })();
+                a = function() {};
+                function h() {
+                    console.log(a);
+                }
+            })("PASS");
+        }
+        f();
+    }
+    expect_stdout: "PASS"
+}
+
+issue_5777_2: {
+    options = {
+        reduce_vars: true,
+        toplevel: true,
+        unused: true,
+    }
+    input: {
+        function f(a) {
+            (function() {
+                function g() {
+                    h();
+                }
+                g();
+                a = function() {};
+                function h() {
+                    console.log(a);
+                }
+            })();
+        }
+        f("PASS");
+    }
+    expect: {
+        (function(a) {
+            (function() {
+                (function() {
+                    h();
+                })();
+                a = function() {};
+                function h() {
+                    console.log(a);
+                }
+            })();
+        })("PASS");
+    }
+    expect_stdout: "PASS"
+}