tweak do-while loops

- `do{...}while(false)` => `{...}`
- clean up `AST_While` logic

closes #1452

lib/compress.js

@@ -1813,8 +1813,14 @@ merge(Compressor.prototype, {
                     extract_declarations_from_unreachable_code(compressor, self.body, a);
                     return make_node(AST_BlockStatement, self, { body: a });
                 }
+            } else {
+                // self instanceof AST_Do
+                return self.body;
             }
         }
+        if (self instanceof AST_While) {
+            return make_node(AST_For, self, self).transform(compressor);
+        }
         return self;
     });
 
@@ -1863,16 +1869,6 @@ merge(Compressor.prototype, {
         }
     };
 
-    OPT(AST_While, function(self, compressor) {
-        if (!compressor.option("loops")) return self;
-        self = AST_DWLoop.prototype.optimize.call(self, compressor);
-        if (self instanceof AST_While) {
-            if_break_in_loop(self, compressor);
-            self = make_node(AST_For, self, self).transform(compressor);
-        }
-        return self;
-    });
-
     OPT(AST_For, function(self, compressor){
         var cond = self.condition;
         if (cond) {

test/compress/loops.js

@@ -187,3 +187,32 @@ keep_collapse_const_in_own_block_scope_2: {
         console.log(c);
     }
 }
+
+evaluate: {
+    options = {
+        loops: true,
+        dead_code: true,
+        evaluate: true,
+    };
+    input: {
+        while (true) {
+            a();
+        }
+        while (false) {
+            b();
+        }
+        do {
+            c();
+        } while (true);
+        do {
+            d();
+        } while (false);
+    }
+    expect: {
+        for(;;)
+            a();
+        for(;;)
+            c();
+        d();
+    }
+}