improve reduce_vars (#2592)

- account for hoisting nature of `var`

lib/compress.js

@@ -381,7 +381,10 @@ merge(Compressor.prototype, {
                     && node.operator == "="
                     && node.left instanceof AST_SymbolRef) {
                     var d = node.left.definition();
-                    if (safe_to_assign(d, node.right)) {
+                    if (safe_to_assign(d, node.right)
+                        || d.fixed === undefined && all(d.orig, function(sym) {
+                            return sym instanceof AST_SymbolVar;
+                        })) {
                         d.references.push(node.left);
                         d.fixed = function() {
                             return node.right;
@@ -561,9 +564,9 @@ merge(Compressor.prototype, {
             if (!safe_to_read(def)) return false;
             if (def.fixed === false) return false;
             if (def.fixed != null && (!value || def.references.length > 0)) return false;
-            return !def.orig.some(function(sym) {
-                return sym instanceof AST_SymbolDefun
-                    || sym instanceof AST_SymbolLambda;
+            return all(def.orig, function(sym) {
+                return !(sym instanceof AST_SymbolDefun
+                    || sym instanceof AST_SymbolLambda);
             });
         }
 

test/compress/reduce_vars.js

@@ -4784,3 +4784,57 @@ escape_local_throw: {
     }
     expect_stdout: "PASS"
 }
+
+inverted_var: {
+    options = {
+        evaluate: true,
+        inline: true,
+        passes: 3,
+        reduce_vars: true,
+        side_effects: true,
+        unused: true,
+    }
+    input: {
+        console.log(function() {
+            var a = 1;
+            return a;
+        }(), function() {
+            var b;
+            b = 2;
+            return b;
+        }(), function() {
+            c = 3;
+            return c;
+            var c;
+        }(), function(c) {
+            c = 4;
+            return c;
+        }(), function (c) {
+            c = 5;
+            return c;
+            var c;
+        }(), function c() {
+            c = 6;
+            return c;
+        }(), function c() {
+            c = 7;
+            return c;
+            var c;
+        }(), function() {
+            c = 8;
+            return c;
+            var c = "foo";
+        }());
+    }
+    expect: {
+        console.log(1, 2, 3, 4, 5, function c() {
+            c = 6;
+            return c;
+        }(), 7, function() {
+            c = 8;
+            return c;
+            var c = "foo";
+        }());
+    }
+    expect_stdout: true
+}