[llvm] [LiveRegUnits] Enhanced the register liveness check (PR #66061)

[Matt Arsenault via llvm-commits]

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@@ -112,13 +112,13 @@ class LiveRegUnits {
   /// The regmask has the same format as the one in the RegMask machine operand.
   void addRegsInMask(const uint32_t *RegMask);
 
-  /// Returns true if no part of physical register \p Reg is live.
-  bool available(MCPhysReg Reg) const {
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arsenm wrote:

I think available should stay as it is here (with rename)? A separate helper can combine the isReserved check 

https://github.com/llvm/llvm-project/pull/66061