[MCP] Use MCRegUnit as the key type of CopyTracker::Copies map. NFC. (#98277)

`CopyTracker` is in fact tracking at RegUnit level, not MCRegister.

Author: Kai Luo

llvm/lib/CodeGen/MachineCopyPropagation.cpp

@@ -65,6 +65,7 @@
 #include "llvm/CodeGen/TargetRegisterInfo.h"
 #include "llvm/CodeGen/TargetSubtargetInfo.h"
 #include "llvm/InitializePasses.h"
+#include "llvm/MC/MCRegister.h"
 #include "llvm/MC/MCRegisterInfo.h"
 #include "llvm/Pass.h"
 #include "llvm/Support/Debug.h"
@@ -112,7 +113,7 @@ class CopyTracker {
     bool Avail;
   };
 
-  DenseMap<MCRegister, CopyInfo> Copies;
+  DenseMap<MCRegUnit, CopyInfo> Copies;
 
 public:
   /// Mark all of the given registers and their subregisters as unavailable for
@@ -251,7 +252,7 @@ class CopyTracker {
     return !Copies.empty();
   }
 
-  MachineInstr *findCopyForUnit(MCRegister RegUnit,
+  MachineInstr *findCopyForUnit(MCRegUnit RegUnit,
                                 const TargetRegisterInfo &TRI,
                                 bool MustBeAvailable = false) {
     auto CI = Copies.find(RegUnit);
@@ -262,7 +263,7 @@ class CopyTracker {
     return CI->second.MI;
   }
 
-  MachineInstr *findCopyDefViaUnit(MCRegister RegUnit,
+  MachineInstr *findCopyDefViaUnit(MCRegUnit RegUnit,
                                    const TargetRegisterInfo &TRI) {
     auto CI = Copies.find(RegUnit);
     if (CI == Copies.end())