[llvm] [MachinePipeliner] Use VirtRegOrUnit instead of Register appropriately (PR #177535)

[Ryotaro Kasuga via llvm-commits]

================
@@ -1588,12 +1580,13 @@ class HighRegisterPressureDetector {
   }
 
   // Return true if Reg is reserved one, for example, stack pointer
-  bool isReservedRegister(Register Reg) const {
-    return Reg.isPhysical() && MRI.isReserved(Reg.asMCReg());
+  bool isReservedRegister(VirtRegOrUnit Reg) const {
----------------
kasuga-fj wrote:

Fixed

https://github.com/llvm/llvm-project/pull/177535