Index: llvm/lib/CodeGen/MachineSink.cpp
===================================================================
--- llvm/lib/CodeGen/MachineSink.cpp
+++ llvm/lib/CodeGen/MachineSink.cpp
@@ -128,10 +128,14 @@
     /// current block.
     DenseSet<DebugVariable> SeenDbgVars;
 
+    // A single DBG_VALUE that is to be sunk, and its original subregister.
+    using SinkingVar = std::pair<MachineInstr *, unsigned>;
+
     /// A set of DBG_VALUEs, indexed by their DebugVariable. Refers to the
     /// original / non-sunk DBG_VALUE, which should be cloned to the final
-    /// sunk location.
-    using SinkingVarSet = DenseMap<DebugVariable, MachineInstr *>;
+    /// sunk location. The subregister the DBG_VALUE originally held is
+    /// stored too, as other salvage operations may change it.
+    using SinkingVarSet = DenseMap<DebugVariable, SinkingVar>;
 
     /// Record of variable locations to re-create after the sinking of a
     /// vreg definition completes.
@@ -370,15 +374,17 @@
     ++DestLoc;
 
     // Collect the DBG_VALUEs being sunk and put them in a deterministic order.
-    using VarInstPair = std::pair<DebugVariable, MachineInstr *>;
+    using VarInstPair = std::pair<DebugVariable, SinkingVar>;
     SmallVector<VarInstPair, 16> InstsToSink;
     for (auto &SunkLoc : Def.InstsToSink)
       InstsToSink.push_back(SunkLoc);
     llvm::sort(InstsToSink);
 
     for (auto &SunkLoc : InstsToSink) {
-      MachineInstr *NewDbgMI = MF.CloneMachineInstr(SunkLoc.second);
+      SinkingVar ToSink = SunkLoc.second;
+      MachineInstr *NewDbgMI = MF.CloneMachineInstr(ToSink.first);
       NewDbgMI->getOperand(0).setReg(VReg);
+      NewDbgMI->getOperand(0).setSubReg(ToSink.second);
       MBB->insert(DestLoc, NewDbgMI);
     }
   }
@@ -1096,7 +1102,8 @@
       // Debug users that don't pass any other DBG_VALUEs for this variable
       // can be sunk.
       if (!User.getInt())
-        SunkDef.InstsToSink.insert({Var, DbgMI});
+        SunkDef.InstsToSink.insert(
+            {Var, {DbgMI, DbgMI->getOperand(0).getSubReg()}});
     }
   }
 
Index: llvm/test/DebugInfo/MIR/X86/machinesink.mir
===================================================================
--- llvm/test/DebugInfo/MIR/X86/machinesink.mir
+++ llvm/test/DebugInfo/MIR/X86/machinesink.mir
@@ -87,7 +87,17 @@
   exit:
     ret void
   }
-  
+
+  define void @test7(i32* nocapture readonly %p) local_unnamed_addr !dbg !601 {
+  ; Stripped
+  entry:
+    br label %nou
+  nou:
+    br label %exit
+  exit:
+    ret void
+  }
+
   declare void @llvm.dbg.value(metadata, i64, metadata, metadata)
 
   !llvm.dbg.cu = !{!1}
@@ -134,6 +144,11 @@
   !502 = !{!503}
   !503 = !DILocalVariable(name: "u", arg: 1, scope: !501, file: !2, line: 2, type: !12)
   !504 = !DILocation(line: 1, column: 1, scope: !501)
+  !601 = distinct !DISubprogram(name: "test5", scope: !2, file: !2, line: 2, type: !10, isLocal: false, isDefinition: true, scopeLine: 3, flags: DIFlagPrototyped, isOptimized: true, unit: !1, retainedNodes: !602)
+  !602 = !{!603}
+  !603 = !DILocalVariable(name: "v", arg: 1, scope: !601, file: !2, line: 2, type: !12)
+  !604 = !DILocation(line: 1, column: 1, scope: !601)
+
 
   ; CHECK: [[VARNUM:![0-9]+]] = !DILocalVariable(name: "p",
   ; CHECK: [[VAR2NUM:![0-9]+]] = !DILocalVariable(name: "q",
@@ -141,6 +156,7 @@
   ; CHECK: [[VAR4NUM:![0-9]+]] = !DILocalVariable(name: "s",
   ; CHECK: [[VAR5NUM:![0-9]+]] = !DILocalVariable(name: "t",
   ; CHECK: [[VAR6NUM:![0-9]+]] = !DILocalVariable(name: "u",
+  ; CHECK: [[VAR7NUM:![0-9]+]] = !DILocalVariable(name: "v",
 
 ...
 ---
@@ -467,3 +483,67 @@
     $rax = MOV64ri 1
     RET 0
 ...
+---
+name:            test7
+# CHECK-LABEL: name: test7
+tracksRegLiveness: true
+liveins:
+  - { reg: '$rdi', virtual-reg: '%2' }
+  - { reg: '$rsi', virtual-reg: '%2' }
+body:             |
+  bb.0.entry:
+    ; CHECK-LABEL: bb.0.entry:
+    ; CHECK-NOT:   DBG_VALUE
+    successors: %bb.3
+    liveins: $rdi, $esi
+    JMP_1 %bb.3
+
+  bb.1:
+    successors: %bb.2, %bb.4
+    liveins: $rdi, $esi
+
+    ; Register %5 sinks through this block; the DBG_VALUE should become $noreg
+    ; CHECK-LABEL: bb.1:
+    ; CHECK:       DBG_VALUE $noreg, $noreg, [[VAR7NUM]], !DIExpression()
+
+    CMP32ri $esi, 1, implicit-def $eflags
+    DBG_VALUE %5, $noreg, !603, !17, debug-location !604
+    JCC_1 %bb.2, 4, implicit $eflags
+    JMP_1 %bb.4
+
+  bb.2:
+    successors: %bb.4
+
+    ; Both copies should sink into this block, and we should sink the DBG_VALUE
+    ; from %bb.1 into this one too. The DBG_VALUE should not pick up a
+    ; subregister along the way.
+    ; CHECK-LABEL: bb.2:
+    ; CHECK:       %[[COPYDEST1:[0-9]+]]:gr32 = COPY %[[COPYSRC1:[0-9]+]].sub_32bit
+    ; CHECK-NEXT: %[[COPYDEST2:[0-9]+]]:gr32 = COPY %[[COPYDEST1]]
+    ; CHECK-NEXT: DBG_VALUE %[[COPYDEST2]], $noreg, [[VAR7NUM]], !DIExpression()
+    ; CHECK-NEXT: ADD32ri
+
+    %1:gr32 = ADD32ri8 %5, 4, implicit-def dead $eflags
+    JMP_1 %bb.4
+
+  bb.3:
+    successors: %bb.1, %bb.4
+    liveins: $rdi, $esi
+
+    ; CHECK-LABEL: bb.3:
+    ; CHECK:       %[[COPYSRC1]]:gr64 = COPY $rdi
+    ; CHECK:       DBG_VALUE $noreg, $noreg, [[VAR7NUM]], !DIExpression()
+
+    %2:gr64 = COPY $rdi
+    %12:gr32 = COPY %2.sub_32bit
+    %5:gr32 = COPY %12
+    CMP32ri $esi, 0, implicit-def $eflags
+    DBG_VALUE %5, $noreg, !603, !17, debug-location !604
+    JCC_1 %bb.1, 4, implicit $eflags
+    JMP_1 %bb.4
+
+  bb.4:
+    liveins: $rdi, $esi
+    $eax = COPY killed $rdi
+    RET 0
+...