Revert "[DebugInfo] Fix updateDbgUsersToReg to support DBG_VALUE_LIST"

This reverts commit 0791f96.

Causing crashes: https://crbug.com/1206764

llvm/include/llvm/CodeGen/MachineRegisterInfo.h

@@ -823,13 +823,12 @@ class MachineRegisterInfo {
 
   /// updateDbgUsersToReg - Update a collection of DBG_VALUE instructions
   /// to refer to the designated register.
-  void updateDbgUsersToReg(Register OldReg, Register NewReg,
-                           ArrayRef<MachineInstr *> Users) const {
+  void updateDbgUsersToReg(Register Reg,
+                           ArrayRef<MachineInstr*> Users) const {
     for (MachineInstr *MI : Users) {
-      assert(MI->isDebugValue());
-      assert(MI->hasDebugOperandForReg(OldReg));
-      for (auto &Op : MI->getDebugOperandsForReg(OldReg))
-        Op.setReg(NewReg);
+      assert(MI->isDebugInstr());
+      assert(MI->getOperand(0).isReg());
+      MI->getOperand(0).setReg(Reg);
     }
   }
 

llvm/lib/CodeGen/MachineCopyPropagation.cpp

@@ -294,7 +294,7 @@ class MachineCopyPropagation : public MachineFunctionPass {
   SmallSetVector<MachineInstr *, 8> MaybeDeadCopies;
 
   /// Multimap tracking debug users in current BB
-  DenseMap<MachineInstr *, SmallSet<MachineInstr *, 2>> CopyDbgUsers;
+  DenseMap<MachineInstr*, SmallVector<MachineInstr*, 2>> CopyDbgUsers;
 
   CopyTracker Tracker;
 
@@ -321,7 +321,7 @@ void MachineCopyPropagation::ReadRegister(MCRegister Reg, MachineInstr &Reader,
         LLVM_DEBUG(dbgs() << "MCP: Copy is used - not dead: "; Copy->dump());
         MaybeDeadCopies.remove(Copy);
       } else {
-        CopyDbgUsers[Copy].insert(&Reader);
+        CopyDbgUsers[Copy].push_back(&Reader);
       }
     }
   }
@@ -734,10 +734,7 @@ void MachineCopyPropagation::ForwardCopyPropagateBlock(MachineBasicBlock &MBB) {
       // Update matching debug values, if any.
       assert(MaybeDead->isCopy());
       Register SrcReg = MaybeDead->getOperand(1).getReg();
-      Register DestReg = MaybeDead->getOperand(0).getReg();
-      SmallVector<MachineInstr *> MaybeDeadDbgUsers(
-          CopyDbgUsers[MaybeDead].begin(), CopyDbgUsers[MaybeDead].end());
-      MRI->updateDbgUsersToReg(DestReg, SrcReg, MaybeDeadDbgUsers);
+      MRI->updateDbgUsersToReg(SrcReg, CopyDbgUsers[MaybeDead]);
 
       MaybeDead->eraseFromParent();
       Changed = true;