fix corner case in reduce_vars (#5517)

fixes #5516

lib/compress.js

@@ -11997,6 +11997,8 @@ Compressor.prototype.compress = function(node) {
                     if ((def.scope !== self.scope.resolve() || def.in_loop)
                         && (!compressor.option("reduce_funcs") || def.escaped.depth == 1 || fixed.inlined)) {
                         single_use = false;
+                    } else if (def.redefined()) {
+                        single_use = false;
                     } else if (recursive_ref(compressor, def, fixed)) {
                         single_use = false;
                     } else if (fixed.name && fixed.name.definition() !== def) {

test/compress/const.js

@@ -1872,3 +1872,37 @@ issue_5476: {
     }
     expect_stdout: "undefined"
 }
+
+issue_5516: {
+    options = {
+        inline: true,
+        reduce_funcs: true,
+        reduce_vars: true,
+        unused: true,
+    }
+    input: {
+        console.log(typeof function() {
+            try {} catch (a) {
+                (function f() {
+                    a;
+                })();
+            }
+            {
+                const a = function() {};
+                return a;
+            }
+        }());
+    }
+    expect: {
+        console.log(typeof function() {
+            try {} catch (a) {
+                void a;
+            }
+            {
+                const a = function() {};
+                return a;
+            }
+        }());
+    }
+    expect_stdout: "function"
+}

test/compress/varify.js

@@ -613,3 +613,35 @@ issue_4954: {
     ]
     node_version: ">=4"
 }
+
+issue_5516: {
+    options = {
+        reduce_funcs: true,
+        reduce_vars: true,
+        unused: true,
+        varify: true,
+    }
+    input: {
+        "use strict";
+        console.log(typeof function() {
+            {
+                let a;
+            }
+            {
+                const a = function() {};
+                return a;
+            }
+        }());
+    }
+    expect: {
+        "use strict";
+        console.log(typeof function() {
+            {
+                const a = function() {};
+                return a;
+            }
+        }());
+    }
+    expect_stdout: "function"
+    node_version: ">=4"
+}