As a continuation of #83109, I audited the places where we iterate over all the registers in LSRA code base. I would categorize it:

• Most of them are in #ifdef DEBUG

• Few are at the beginning of methods like allocateRegister() and resolveRegister(). The one in allocateRegister() can be done better during RegisterRecord initialization perhaps or creating intervals.

• Then, there are instances where they happen during building interval or allocation.

  • In resetAllRegistersState(), we reset the assigned interval at block boundaries for minopts.
  • In processStartBlockStartLocations(), we can optimize it to just iterate on liveRegs mask with bitwise iterator instead of for-loop.
  • In addRefsForPhysRegMask() - Used during kill positions, Here too, should be able to use bitwise iterator or bitscanforward technique.