diff -r 5c30fa1c8c5b -r 6c1fa412c72d rt/vm/src/main/java/org/apidesign/vm4brwsr/Bck2Brwsr.java
--- a/rt/vm/src/main/java/org/apidesign/vm4brwsr/Bck2Brwsr.java	Thu Mar 12 10:32:13 2015 +0100
+++ b/rt/vm/src/main/java/org/apidesign/vm4brwsr/Bck2Brwsr.java	Fri Mar 13 11:41:04 2015 +0100
@@ -422,8 +422,10 @@
      */
     public static final class Flow {
         private final MethodData m;
+        private byte[] ops;
         Flow(MethodData m) {
             this.m = m;
+            ops = new byte[m.getCode().length];
         }
         
         /** Access to bytecode of the method to analyse.
@@ -441,10 +443,46 @@
             return m.getName();
         }
         
-        public void registerCycle(int offset) {
+        public void beginLoopAt(int bci) {
+            ops[bci] |= 0x10;
         }
         
-        public void registerIf(int offset) {
+        public void beginIfAt(int bci) {
+            ops[bci] |= 0x20;
+        }
+
+
+        public void breakAt(int bci) {
+            ops[bci] |= 0x40;
+        }
+
+        public void beginElseAt(int bci) {
+            ops[bci] |= 0x80;
+        }
+
+        public void endAt(int bci) {
+            int cnt = (ops[bci] & 0x0f) + 1;
+            int rest = ops[bci] & 0xf0;
+            ops[bci] = (byte)(rest | cnt);
+        }
+        
+        boolean isFlow(int at) {
+            return ops[at] != 0;
+        }
+        boolean isLoop(int at) {
+            return (ops[at] & 0x10) != 0;
+        }
+        boolean isIf(int at) {
+            return (ops[at] & 0x20) != 0;
+        }
+        boolean isBreak(int at) {
+            return (ops[at] & 0x40) != 0;
+        }
+        boolean isElse(int at) {
+            return (ops[at] & 0x80) != 0;
+        }
+        int isEnd(int at) {
+            return (ops[at] & 0x0f);
         }
         
         /** Provider of advanced analysis of the code flow inside of