the storage of !dbg metadata kinds in the instruction themselves.
The on-the-side hash table works great for metadata that not-all
instructions get, or for metadata that only exists when optimizing.
But when compile-time is everything, it isn't great.
I'm not super thrilled with the fact that this plops a TrackingVH in
Instruction, because it grows it by 3 words. I'm investigating
alternatives, but this should be a step in the right direction in any
case.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@99957 91177308-0d34-0410-b5e6-96231b3b80d8
ec39f095f5