V4 JIT: add hint for phi-node operands.

Not only is it preferable for the target of a phi-node to be stored in
the same location as one of the sources, but the same yields for the
sources. For example, in a loop, it is preferable to store the result
of a value used in a phi-node in the loop header to be stored in the
same location as that phi-node's target. Doing that will eliminate extra
moves that are generated to resolve differences between edges.

Change-Id: I0cb5fbe8915d602ac9b9a2a7e8b95cf47b1efb68
Reviewed-by: Lars Knoll <lars.knoll@digia.com>
V4 JIT: add some documentation and literature references.

Change-Id: I67667b74672b94b951361bf2a446476edf44b826
Reviewed-by: Lars Knoll <lars.knoll@digia.com>