fix corner case in merge_vars (#5715)

fixes #5714

lib/compress.js

@@ -6662,15 +6662,15 @@ Compressor.prototype.compress = function(node) {
             do {
                 var head = first.shift();
                 if (tail.index > head.index) continue;
-                var id = head.definition.id;
+                var prev_def = head.definition;
-                if (!(id in prev)) continue;
+                if (!(prev_def.id in prev)) continue;
-                var head_refs = references[id];
+                var head_refs = references[prev_def.id];
                 if (!head_refs) continue;
                 if (head_refs.start.block !== tail_refs.start.block
                     || !mergeable(head_refs, tail_refs)
                     || (head_refs.start.loop || !same_scope(def)) && !mergeable(tail_refs, head_refs)
-                    || compressor.option("webkit") && is_funarg(def) !== is_funarg(head.definition)
+                    || compressor.option("webkit") && is_funarg(def) !== is_funarg(prev_def)
-                    || head.definition.const_redefs
+                    || prev_def.const_redefs
                     || !all(head_refs.scopes, function(scope) {
                         return scope.find_variable(def.name) === def;
                     })) {
@@ -6682,12 +6682,14 @@ Compressor.prototype.compress = function(node) {
                     sym.name = def.name;
                     if (sym instanceof AST_SymbolRef) {
                         def.references.push(sym);
+                        prev_def.replaced++;
                     } else {
                         def.orig.push(sym);
+                        prev_def.eliminated++;
                     }
                 });
-                if (!head.definition.fixed) def.fixed = false;
+                if (!prev_def.fixed) def.fixed = false;
-                merged[id] = def;
+                merged[prev_def.id] = def;
                 changed = true;
                 break;
             } while (first.length);

test/compress/merge_vars.js

@@ -3845,3 +3845,47 @@ issue_5471_2: {
     }
     expect_stdout: "PASS"
 }
+
+issue_5714: {
+    options = {
+        inline: true,
+        join_vars: true,
+        loops: true,
+        merge_vars: true,
+        unused: true,
+    }
+    input: {
+        "use strict";
+        console.log(function() {
+            var i = 1;
+            while (i--) {
+                var a = function f(b) {
+                    console.log(b);
+                    var c = function(d) {
+                        console.log(typeof d);
+                    }(console);
+                }();
+                var e = 42;
+            }
+            return e;
+        }());
+    }
+    expect: {
+        "use strict";
+        console.log(function() {
+            for (var i = 1; i--;) {
+                var b = void 0;
+                console.log(b);
+                b = console,
+                console.log(typeof b);
+                var e = 42;
+            }
+            return e;
+        }());
+    }
+    expect_stdout: [
+        "undefined",
+        "object",
+        "42",
+    ]
+}