fix corner cases related to in (#3964)

test/compress/collapse_vars.js

@@ -8164,3 +8164,34 @@ issue_3927: {
     }
     expect_stdout: "PASS"
 }
+
+operator_in: {
+    options = {
+        collapse_vars: true,
+    }
+    input: {
+        function log(msg) {
+            console.log(msg);
+        }
+        var a = "FAIL";
+        try {
+            a = "PASS";
+            0 in null;
+            log("FAIL", a);
+        } catch (e) {}
+        log(a);
+    }
+    expect: {
+        function log(msg) {
+            console.log(msg);
+        }
+        var a = "FAIL";
+        try {
+            a = "PASS";
+            0 in null;
+            log("FAIL", a);
+        } catch (e) {}
+        log(a);
+    }
+    expect_stdout: "PASS"
+}

test/compress/pure_funcs.js

@@ -136,7 +136,7 @@ relational: {
         side_effects :true,
     }
     input: {
-        foo() in foo();
+        foo() in new foo();
         foo() instanceof bar();
         foo() < "bar";
         bar() > foo();

test/compress/side_effects.js

@@ -274,3 +274,26 @@ drop_value: {
         foo(), bar();
     }
 }
+
+operator_in: {
+    options = {
+        side_effects: true,
+    }
+    input: {
+        try {
+            "foo" in true;
+            console.log("FAIL");
+        } catch (e) {
+            console.log("PASS");
+        }
+    }
+    expect: {
+        try {
+            0 in true;
+            console.log("FAIL");
+        } catch (e) {
+            console.log("PASS");
+        }
+    }
+    expect_stdout: "PASS"
+}