RFR(XS): 8216549: Mismatched unsafe access to non escaping object fails

[Roland Westrelin]

http://cr.openjdk.java.net/~roland/8216549/webrev.00/

test1(), test2() and test3() perform an unsafe access with a mismatched
access.

test1() compiles to an unschedulable graph and causes the compiler to
crash. The memory input of the load from a non escaping allocation
initially points to a membar but is set to bypass the membar while
control stays set to the membar. The load is not eliminated because it's
a mismatched memory access, an anti dependence is added between the
membar and the load and the graph is unschedulable.

test2() and test3() return wrong results: the access is mismatched and
misaligned, it's given its own alias by c2 but the MergeMem right after
the allocation only points to the allocation for actual fields of the
newly allocated object. So the load memory input is set to the memory
state on method entry and the load is optimized as zero.

I simply propose to make non escaping allocations with mismatched
accesses to be non scalar replaceable.

Roland.