[llvm] [GlobalISel] Reserve IRTranslator value map and virtual register storage (NFC) (PR #222311)

[Alexis Engelke via llvm-commits]

https://github.com/aengelke commented:

Is this also beneficial in cycles? BB.size() is a linked list traversal, probably with a lot of cache misses.

https://github.com/llvm/llvm-project/pull/222311