Index: llvm/lib/CodeGen/LiveRangeEdit.cpp
===================================================================
--- llvm/lib/CodeGen/LiveRangeEdit.cpp
+++ llvm/lib/CodeGen/LiveRangeEdit.cpp
@@ -134,9 +134,11 @@
       return false;
 
     // Check that subrange is live at UseIdx.
-    if (MO.getSubReg()) {
+    if (li.hasSubRanges()) {
       const TargetRegisterInfo *TRI = MRI.getTargetRegisterInfo();
-      LaneBitmask LM = TRI->getSubRegIndexLaneMask(MO.getSubReg());
+      unsigned SubReg = MO.getSubReg();
+      LaneBitmask LM = SubReg ? TRI->getSubRegIndexLaneMask(SubReg)
+                              : MRI.getMaxLaneMaskForVReg(MO.getReg());
       for (LiveInterval::SubRange &SR : li.subranges()) {
         if ((SR.LaneMask & LM).none())
           continue;
Index: llvm/test/CodeGen/AMDGPU/remat-dead-subreg.mir
===================================================================
--- llvm/test/CodeGen/AMDGPU/remat-dead-subreg.mir
+++ llvm/test/CodeGen/AMDGPU/remat-dead-subreg.mir
@@ -79,3 +79,28 @@
     %6:vreg_64 = V_MOV_B64_PSEUDO %2, implicit $exec
     S_NOP 0, implicit %1.sub0, implicit %1.sub3
 ...
+---
+name:            dead_subreg_whole_reg
+tracksRegLiveness: true
+body:             |
+  bb.0.entry:
+    ; GCN-LABEL: name: dead_subreg_whole_reg
+    ; GCN: $m0 = IMPLICIT_DEF
+    ; GCN-NEXT: renamable $sgpr0_sgpr1 = S_MOV_B64 1, implicit $m0
+    ; GCN-NEXT: renamable $sgpr2_sgpr3 = S_MOV_B64 renamable $sgpr0_sgpr1
+    ; GCN-NEXT: SI_SPILL_S64_SAVE killed renamable $sgpr2_sgpr3, %stack.0, implicit $exec, implicit $sp_reg :: (store (s64) into %stack.0, align 4, addrspace 5)
+    ; GCN-NEXT: renamable $sgpr4_sgpr5 = S_MOV_B64 2, implicit $m0
+    ; GCN-NEXT: renamable $sgpr2_sgpr3 = S_MOV_B64 3, implicit $m0
+    ; GCN-NEXT: dead %4:vgpr_32 = V_MOV_B32_e32 $sgpr0, implicit $exec, implicit killed $sgpr4_sgpr5, implicit killed $sgpr2_sgpr3
+    ; GCN-NEXT: renamable $sgpr2_sgpr3 = SI_SPILL_S64_RESTORE %stack.0, implicit $exec, implicit $sp_reg :: (load (s64) from %stack.0, align 4, addrspace 5)
+    ; GCN-NEXT: dead %5:vreg_64 = V_MOV_B64_PSEUDO killed $sgpr2_sgpr3, implicit $exec
+    ; GCN-NEXT: S_NOP 0, implicit killed renamable $sgpr0
+    $m0 = IMPLICIT_DEF
+    %0:sreg_64_xexec = S_MOV_B64 1, implicit $m0
+    %1:sreg_64 = S_MOV_B64 %0:sreg_64_xexec
+    %2:sreg_64 = S_MOV_B64 2, implicit $m0
+    %3:sreg_64 = S_MOV_B64 3, implicit $m0
+    %4:vgpr_32 = V_MOV_B32_e32 %0.sub0:sreg_64_xexec, implicit $exec, implicit %2, implicit %3
+    %5:vreg_64 = V_MOV_B64_PSEUDO %1, implicit $exec
+    S_NOP 0, implicit %0.sub0
+...