[CodeGen] Optimize/simplify finalizeBundle. NFC (#155448)

When tracking defs in finalizeBundle two sets are used. LocalDefs is
used to track defined virtual and physical registers, while LocalDefsP
is used to track defined register units for the physical registers.

This patch moves the updates of LocalDefsP to only iterate over regunits
when a new physical register is added to LocalDefs. When the physical
register already is present in LocalDefs, then the corresponding
register units are present in LocalDefsP. So it was a waste of time to
add them to the set again.

Author: bjope

llvm/lib/CodeGen/MachineInstrBundle.cpp

@@ -173,6 +173,9 @@ void llvm::finalizeBundle(MachineBasicBlock &MBB,
       if (LocalDefs.insert(Reg)) {
         if (MO.isDead())
           DeadDefSet.insert(Reg);
+        else if (Reg.isPhysical())
+          for (MCRegUnit Unit : TRI->regunits(Reg.asMCReg()))
+            LocalDefsP.set(Unit);
       } else {
         // Re-defined inside the bundle, it's no longer killed.
         KilledDefSet.erase(Reg);
@@ -181,11 +184,6 @@ void llvm::finalizeBundle(MachineBasicBlock &MBB,
           DeadDefSet.erase(Reg);
         }
       }
-
-      if (!MO.isDead() && Reg.isPhysical()) {
-        for (MCRegUnit Unit : TRI->regunits(Reg.asMCReg()))
-          LocalDefsP.set(Unit);
-      }
     }
 
     // Set FrameSetup/FrameDestroy for the bundle. If any of the instructions