scan within IIFEs of assigned values (#2702)

fixes #2701

lib/compress.js

@@ -4913,9 +4913,8 @@ merge(Compressor.prototype, {
             if (reachable) return true;
             if (node instanceof AST_Scope && node !== self) {
                 var parent = scan_scope.parent();
-                if (!(parent instanceof AST_Call && parent.expression === node)) {
+                if (parent instanceof AST_Call && parent.expression === node) return;
                 node.walk(find_ref);
-                }
                 return true;
             }
         });

test/compress/dead-code.js

@@ -881,3 +881,31 @@ issue_2692: {
     }
     expect_stdout: "function"
 }
+
+issue_2701: {
+    options = {
+        dead_code: true,
+        inline: false,
+    }
+    input: {
+        function f(a) {
+            return a = function() {
+                return function() {
+                    return a;
+                };
+            }();
+        }
+        console.log(typeof f()());
+    }
+    expect: {
+        function f(a) {
+            return a = function() {
+                return function() {
+                    return a;
+                };
+            }();
+        }
+        console.log(typeof f()());
+    }
+    expect_stdout: "function"
+}