swift234

SIL Serializer: fix a bug in handling of forward-referenced values.

In serializer, we pre-assign a value ID in order, to each basic block
argument and each SILInstruction that has a value.
In deserializer, we use LocalValues to store the definitions and
ForwardMRVLocalValues for forward-referenced values (values that are
used but not yet defined). LocalValues are updated in setLocalValue where
the ID passed in assumes the same ordering as in serializer: in-order
for each basic block argument and each SILInstruction that has a value.
We update ForwardMRVLocalValues in getLocalValue and when a value is defined
in setLocalValue, the corresponding entry in ForwardMRVLocalValues will be
erased.

rdar://15351123


Swift SVN r9884