RFR(M): 8182471: [MVT] Eliminate redundant value type allocations

[Roland Westrelin]

> http://cr.openjdk.java.net/~thartmann/valhalla/vt_prototype/webrev.20/

callnode.hpp

849     fields[ValueNode]   = Type::TOP;

Type::TOP is strange here. Type::BOTTOM instead?

Shouldn't remove_redundant_allocations() be called from
split_if_with_blocks_post instead? As it is, you're potentially
disconnecting the allocation and split_if_with_blocks_pre will try to
follow its uses so wouldn't it stop halfway through the graph?

Why do you need the dead_allocations list in
ValueTypeNode::remove_redundant_allocations()?

Roland.