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.
Transfer is the terminology that we are using for something be transferred
across an isolation boundary, not consume. This also eliminates confusion with
consume which is a term being used around ownership.
Instead of setting the parent pointer to null, set the `lastInitializedBitfieldID` to -1.
This allows to keep the parent block information, even when an instruction is removed from it's list.
It's used to implement `InstructionSet` and `ValueSet`: sets of SILValues and SILInstructions.
Just like `BasicBlockSet` for basic blocks, the set is implemented by setting bits directly in SILNode.
This is super efficient because insertion and deletion to/from the set are basic bit operations.
The cost is an additional word in SILNode. But this is basically negligible: it just adds ~0.7% of memory used for SILInstructions.
In my experiments, I didn't see any relevant changes in memory consumption or compile time.
* add a BasicBlockSetVector class
* add a second argument to BasicBlockFlag::set, for the set value.
* rename BasicBlockSet::remove -> BasicBlockSet::erase.
* add a MaxBitfieldID statistics value in SILFunction.cpp
