[DeLICM] Allow non-injective PHIRead->PHIWrite mapping.

Remove an assertion that tests the injectivity of the
PHIRead -> PHIWrite relation.  That is, allow a single PHI write to be
used by multiple PHI reads.  This may happen due to some statements
containing the PHI write not having the statement instances that would
overwrite the previous incoming value due to (assumed/invalid) contexts.
This result in that PHI write is mapped to multiple targets which is not
supported.  Codegen will select one one of the targets using
getAddressFunction().  However, the runtime check should protect us from
this case ever being executed.

We therefore allow injective PHI relations.  Additional calculations to
detect/santitize this case would probably not be worth the compuational
effort.

This fixes llvm.org/PR34485

llvm-svn: 313902