[llvm] [CodeGen][MachineLICM] Use RegUnits in HoistRegionPostRA (PR #94608)

[Matt Arsenault via llvm-commits]

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@@ -423,10 +423,47 @@ static bool InstructionStoresToFI(const MachineInstr *MI, int FI) {
   return false;
 }
 
+static void applyBitsNotInRegMaskToRegUnitsMask(const TargetRegisterInfo *TRI,
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arsenm wrote:

const ref.

This whole thing should probably be a helper somewhere else, but it's OK to move it in a later commit. 

https://github.com/llvm/llvm-project/pull/94608