RFR S 8214742 [lworld][c1] Block merging need to preserve type info for flattened arrays

[Ioi Lam]

https://bugs.openjdk.java.net/browse/JDK-8214742
http://cr.openjdk.java.net/~iklam/valhalla/8214742-preserve-typeinfo-for-flattened-array.v01/

The fix is for code like this, where the aaload bytecode needs to know 
that the array is flattened.

     static int test(boolean b) {
         VT[] va;
         if (b) {
             va = new VT[5];
         } else {
             va = new VT[10];
         }
         return va[0].v1;  <<<< here
     }

Thanks

- Ioi