OSR only at loop headers.

interpreter.ts

@@ -108,8 +108,6 @@ module J2ME {
 
   export var onStackReplacementCount = 0;
 
-  export var onStackReplacementIsEnabled = true;
-
   /**
    * Temporarily used for fn.apply.
    */
@@ -260,12 +258,20 @@ module J2ME {
       try {
         if (frame.pc < lastPC) {
           mi.backwardsBranchCount ++;
-          if (onStackReplacementIsEnabled && mi.state === MethodState.Compiled) {
+          if (enableOnStackReplacement && mi.state === MethodState.Compiled) {
             // Just because we've jumped backwards doesn't mean we are at a loop header but it does mean that we are
             // at the beggining of a basic block. This is a really cheap test and a convenient place to perform an
             // on stack replacement.
 
-            profile && onStackReplacementCount ++;
+            var blockMap = mi.blockMap;
+            if (!blockMap) {
+              blockMap = new BlockMap(mi);
+              blockMap.build();
+              mi.blockMap = blockMap;
+            }
+
+            if (blockMap.getBlock(frame.pc).isLoopHeader) {
+              profile && onStackReplacementCount++;
 
               // The current frame will be swapped out for a JIT frame, so pop it off the interpreter stack.
               frames.pop();
@@ -276,16 +282,6 @@ module J2ME {
               // Set the global OSR frame to the current frame.
               O = frame;
 
-            var blockMap = O.methodInfo.blockMap;
-            if (!blockMap) {
-              blockMap = new BlockMap(O.methodInfo);
-              blockMap.build();
-              O.methodInfo.blockMap = blockMap;
-            }
-
-            // Convert between PC and block ID which is what the baseline JIT expects as the PC.
-            O.pc = blockMap.getBlock(O.pc).blockID;
-
               // Set the current frame before doing the OSR in case an exception is thrown.
               frame = frames[frames.length - 1];
 
@@ -314,6 +310,7 @@ module J2ME {
               }
             }
           }
+        }
 
         lastPC = frame.opPC = frame.pc;
         var op: Bytecodes = frame.read8();

runtime.ts

@@ -28,6 +28,11 @@ module J2ME {
    */
   export var enableRuntimeCompilation = true;
 
+  /**
+   * Turns on onStackReplacement
+   */
+  export var enableOnStackReplacement = true;
+
   /**
    * Enables more compact mangled names. This helps reduce code size but may cause naming collisions.
    */