[llvm] [SSAUpdater] Don't use large SmallSets for IDFcalc (PR #97823)

[Jeremy Morse via llvm-commits]

jmorse wrote:

Added a SmallPtrSet reserve method and switched the relevant containers back to SmallPtrSet. I stuck it on the compile-time-tracker and got the same speedup: http://llvm-compile-time-tracker.com/compare.php?from=00c622e596f918d9d83674b58097c8982ae1af95&to=ab267cc31f01dcc088c4839a4fadd3eca92b902f&stat=instructions%3Au

https://github.com/llvm/llvm-project/pull/97823