optimise do{...}while(false) (#1785)

- better heuristics to avoid issues like #1532
- fix `TreeWalker.loopcontrol_target()`
  - `continue` cannot refer to `switch` blocks

test/compress/loops.js

@@ -215,8 +215,7 @@ evaluate: {
             a();
         for(;;)
             c();
-        // rule disabled due to issue_1532
-        do d(); while (false);
+        d();
     }
 }
 
@@ -458,3 +457,26 @@ issue_1648: {
     }
     expect_exact: "function f(){for(x();1;);}"
 }
+
+do_switch: {
+    options = {
+        evaluate: true,
+        loops: true,
+    }
+    input: {
+        do {
+            switch (a) {
+              case b:
+                continue;
+            }
+        } while (false);
+    }
+    expect: {
+        do {
+            switch (a) {
+              case b:
+                continue;
+            }
+        } while (false);
+    }
+}