diff --git a/llvm/lib/CodeGen/RegisterCoalescer.cpp b/llvm/lib/CodeGen/RegisterCoalescer.cpp
--- a/llvm/lib/CodeGen/RegisterCoalescer.cpp
+++ b/llvm/lib/CodeGen/RegisterCoalescer.cpp
@@ -153,12 +153,6 @@
     using DbgValueLoc = std::pair<SlotIndex, MachineInstr*>;
     DenseMap<Register, std::vector<DbgValueLoc>> DbgVRegToValues;
 
-    /// VRegs may be repeatedly coalesced, and have many DBG_VALUEs attached.
-    /// To avoid repeatedly merging sets of DbgValueLocs, instead record
-    /// which vregs have been coalesced, and where to. This map is from
-    /// vreg => {set of vregs merged in}.
-    DenseMap<Register, SmallVector<Register, 4>> DbgMergedVRegNums;
-
     /// A LaneMask to remember on which subregister live ranges we need to call
     /// shrinkToUses() later.
     LaneBitmask ShrinkMask;
@@ -3768,18 +3762,9 @@
     checkMergingChangesDbgValuesImpl(Reg, LHS, RHS, RHSVals);
   };
 
-  // Scan for potentially unsound DBG_VALUEs: examine first the register number
-  // Reg, and then any other vregs that may have been merged into  it.
-  auto PerformScan = [this](Register Reg, std::function<void(Register)> Func) {
-    Func(Reg);
-    if (DbgMergedVRegNums.count(Reg))
-      for (Register X : DbgMergedVRegNums[Reg])
-        Func(X);
-  };
-
   // Scan for unsound updates of both the source and destination register.
-  PerformScan(CP.getSrcReg(), ScanForSrcReg);
-  PerformScan(CP.getDstReg(), ScanForDstReg);
+  ScanForSrcReg(CP.getSrcReg());
+  ScanForDstReg(CP.getDstReg());
 }
 
 void RegisterCoalescer::checkMergingChangesDbgValuesImpl(Register Reg,
@@ -4160,7 +4145,6 @@
     MF->verify(this, "Before register coalescing");
 
   DbgVRegToValues.clear();
-  DbgMergedVRegNums.clear();
   buildVRegToDbgValueMap(fn);
 
   RegClassInfo.runOnMachineFunction(fn);