[NFC][LLVM] Code cleanup in MIRNamerPass.cpp (#162996)

Author: jurahul

llvm/lib/CodeGen/MIRNamerPass.cpp

@@ -23,10 +23,6 @@
 
 using namespace llvm;
 
-namespace llvm {
-extern char &MIRNamerID;
-} // namespace llvm
-
 #define DEBUG_TYPE "mir-namer"
 
 namespace {
@@ -53,10 +49,9 @@ class MIRNamer : public MachineFunctionPass {
 
     VRegRenamer Renamer(MF.getRegInfo());
 
-    unsigned BBIndex = 0;
     ReversePostOrderTraversal<MachineBasicBlock *> RPOT(&*MF.begin());
-    for (auto &MBB : RPOT)
-      Changed |= Renamer.renameVRegs(MBB, BBIndex++);
+    for (const auto &[BBIndex, MBB] : enumerate(RPOT))
+      Changed |= Renamer.renameVRegs(MBB, BBIndex);
 
     return Changed;
   }
@@ -66,10 +61,4 @@ class MIRNamer : public MachineFunctionPass {
 
 char MIRNamer::ID;
 
-char &llvm::MIRNamerID = MIRNamer::ID;
-
-INITIALIZE_PASS_BEGIN(MIRNamer, "mir-namer", "Rename Register Operands", false,
-                      false)
-
-INITIALIZE_PASS_END(MIRNamer, "mir-namer", "Rename Register Operands", false,
-                    false)
+INITIALIZE_PASS(MIRNamer, "mir-namer", "Rename Register Operands", false, false)