review (XS) for 6969586: OptimizeStringConcat: SIGSEGV in LoadNode::Value()

[Tom Rodriguez]

http://cr.openjdk.java.net/~never/6969586

6969586: OptimizeStringConcat: SIGSEGV in LoadNode::Value()
Reviewed-by:

The logic in memnode that tries to constant fold loads from constant
Strings doesn't handle a NULL base properly leading to a SEGV.  The
fix is to test if the type is a really a constant TypeOopPtr instead
of testing that the node is a ConP.  Tested with failing CTW test
case.