Specifically:
1. I changed Partition::apply so that it has an emitLog flag. The reason why I
did this is we run apply in a few different situations sometimes when we want to
emit logging other times when we really don't. For instance, we want to emit
logging when walking instructions and updating the entry partition. On the other
hand, we do not want to emit logging if we apply a value to a partition while
attempting to determine why an error needed to be emitted.
2. When we create an assign partition op and we see that our destination and
source are the same representative, we do not create the actual assign. Before
we did not log this so it looked like there was a logic error that was stopping
us from emitting a partition op when visiting said instructions. Now, we emit a
small logging message so it isn't possible to be confused.
3. Since I am adding another parameter to Partition::apply, I decided to
refactor Partition::apply to be in a separate PartitionOpEvaluator data
structure that contains the options that we used to pass into Partition::apply.
This prevents any mistakes around configuring Partition::apply since the fields
provide nice names/common sense default values.
We were performing a union on the intersection of the lhs/rhs but were dropping
the parts of lhs/rhs that were in the symmetric difference of the two sets.
Without this, we would not diagnose cases like this where we had elements on the
lhs/rhs that were not in the intersection.
```
var closure: () -> () = {}
await transferToMain(closure)
if await booleanFlag {
closure = {
print(self.klass)
}
} else {
closure = {}
}
// At this point we would lose closure since they were different elements
await transferToMain(closure) // We wouldn't error on this!
```
rdar://117437059
This is the correct thing to do since the header is in SILOptimizer. That being
said the reason why I am doing this is that I want to add a command line flag to
PartitionUtils.h to allow for more verbose debug output and the flag's
definition will be in the SILOptimizer library. So this is just a little cleanup
that follows from that.
