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

[Matt Arsenault via llvm-commits]

================
@@ -41,6 +41,11 @@ void LiveRegUnits::addRegsInMask(const uint32_t *RegMask) {
   }
 }
 
+bool LiveRegUnits::available(const MachineRegisterInfo &MRI,
+                             MCPhysReg Reg) const {
+  return !MRI.isReserved(Reg) && !contains(Reg);
----------------
arsenm wrote:

swap the order of the checks 

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