fix corner case in hoist_vars (#4739)

fixes #4736

lib/compress.js

@@ -6821,18 +6821,14 @@ merge(Compressor.prototype, {
         if (vars_found > 0) {
             // collect only vars which don't show up in self's arguments list
             var defs = [];
+            if (self instanceof AST_Lambda) self.each_argname(function(argname) {
+                vars.del(argname.name);
+            });
             vars.each(function(def, name) {
-                if (self instanceof AST_Lambda
-                    && !all(self.argnames, function(argname) {
-                        return argname.name != name;
-                    })) {
-                    vars.del(name);
-                } else {
                 def = def.clone();
                 def.value = null;
                 defs.push(def);
                 vars.set(name, def);
-                }
             });
             if (defs.length > 0) {
                 // try to merge in assignments
@@ -6856,7 +6852,7 @@ merge(Compressor.prototype, {
                         && vars.has(sym.name)) {
                         var def = vars.get(sym.name);
                         if (def.value) break;
-                        def.value = expr.right;
+                        def.value = expr.right.clone();
                         remove(defs, def);
                         defs.push(def);
                         body.shift();

test/compress/hoist_vars.js

@@ -140,6 +140,7 @@ issue_4487: {
         functions: true,
         hoist_vars: true,
         keep_fnames: true,
+        passes: 2,
         reduce_vars: true,
         toplevel: true,
         unused: true,
@@ -207,3 +208,35 @@ issue_4517: {
     }
     expect_stdout: "2boolean"
 }
+
+issue_4736: {
+    options = {
+        collapse_vars: true,
+        evaluate: true,
+        hoist_vars: true,
+        merge_vars: true,
+        reduce_vars: true,
+        toplevel: true,
+        unused: true,
+    }
+    input: {
+        var a;
+        function f() {
+            (function g() {
+                var b = (a = 0, 1 << 30);
+                var c = (a = 0, console.log(b));
+                var d = c;
+            })(f);
+        }
+        f();
+    }
+    expect: {
+        (function() {
+            (function() {
+                0,
+                console.log(1073741824);
+            })();
+        })();
+    }
+    expect_stdout: "1073741824"
+}