avoid evaluate of compound assignment after dead_code transform (#2861)

fixes #2860

test/compress/reduce_vars.js

@@ -5467,3 +5467,43 @@ chained_assignments: {
     }
     expect_stdout: "5eadbeef"
 }
+
+issue_2860_1: {
+    options = {
+        dead_code: true,
+        evaluate: true,
+        reduce_vars: true,
+    }
+    input: {
+        console.log(function(a) {
+            return a ^= 1;
+            a ^= 2;
+        }());
+    }
+    expect: {
+        console.log(function(a) {
+            return 1 ^ a;
+        }());
+    }
+    expect_stdout: "1"
+}
+
+issue_2860_2: {
+    options = {
+        dead_code: true,
+        evaluate: true,
+        inline: true,
+        passes: 2,
+        reduce_vars: true,
+    }
+    input: {
+        console.log(function(a) {
+            return a ^= 1;
+            a ^= 2;
+        }());
+    }
+    expect: {
+        console.log(1);
+    }
+    expect_stdout: "1"
+}