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
@@ -1213,7 +1213,10 @@
       }
       ++I;
     }
-    LIS->extendToIndices(SR, EndPoints);
+    SmallVector<SlotIndex, 8> Undefs;
+    IntB.computeSubRangeUndefs(Undefs, SR.LaneMask, *MRI,
+                               *LIS->getSlotIndexes());
+    LIS->extendToIndices(SR, EndPoints, Undefs);
   }
   // If any dead defs were extended, truncate them.
   shrinkToUses(&IntB);
diff --git a/llvm/test/CodeGen/AMDGPU/coalescer-removepartial-extend-undef-subrange.mir b/llvm/test/CodeGen/AMDGPU/coalescer-removepartial-extend-undef-subrange.mir
new file mode 100644
--- /dev/null
+++ b/llvm/test/CodeGen/AMDGPU/coalescer-removepartial-extend-undef-subrange.mir
@@ -0,0 +1,74 @@
+# NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py
+# RUN: llc -march=amdgcn -mcpu=gfx900 -run-pass simple-register-coalescing -verify-machineinstrs -o - %s | FileCheck %s
+#
+# The failure occurs when the coalescer tries to removePartialRedundency() on the
+# "%2:vreg_64 = COPY %3" in bb.1. The coalescer tries to prune and extend each
+# subrange of %2, the subrange for %2.sub1 has a def location (in bb.2) in the
+# predecessor path 2->3->1. But for another predecessor path 0->4->1,
+# the subrange has only one undef location in bb.0. If we don't compute Undef set,
+# it will fail to find the reaching def for %2.sub1 in predecessor bb.4 and bb.0
+# and crash with error message:
+# "Use of $noreg does not have a corresponding definition on every path
+#  LLVM ERROR: Use not jointly dominated by defs"
+
+---
+name:            _amdgpu_ps_main
+alignment:       1
+tracksRegLiveness: true
+body:             |
+  ; CHECK-LABEL: name: _amdgpu_ps_main
+  ; CHECK: bb.0:
+  ; CHECK:   successors: %bb.2(0x40000000), %bb.4(0x40000000)
+  ; CHECK:   liveins: $sgpr2, $sgpr3, $vgpr3
+  ; CHECK:   [[COPY:%[0-9]+]]:sgpr_32 = COPY $sgpr2
+  ; CHECK:   undef %1.sub0:vreg_64 = COPY [[COPY]]
+  ; CHECK:   undef %2.sub0:vreg_64 = COPY [[COPY]]
+  ; CHECK:   S_CBRANCH_VCCNZ %bb.2, implicit undef $vcc
+  ; CHECK:   S_BRANCH %bb.4
+  ; CHECK: bb.1:
+  ; CHECK:   successors: %bb.2(0x80000000)
+  ; CHECK:   S_NOP 0, implicit %2.sub0
+  ; CHECK: bb.2:
+  ; CHECK:   successors: %bb.3(0x04000000), %bb.2(0x7c000000)
+  ; CHECK:   [[COPY1:%[0-9]+]]:vreg_64 = COPY %2
+  ; CHECK:   %1.sub0:vreg_64 = COPY [[COPY1]].sub0
+  ; CHECK:   %2:vreg_64 = COPY %1
+  ; CHECK:   S_CBRANCH_EXECNZ %bb.2, implicit undef $exec
+  ; CHECK:   S_BRANCH %bb.3
+  ; CHECK: bb.3:
+  ; CHECK:   successors: %bb.1(0x80000000)
+  ; CHECK:   %2:vreg_64 = COPY [[COPY1]]
+  ; CHECK:   S_BRANCH %bb.1
+  ; CHECK: bb.4:
+  ; CHECK:   successors: %bb.1(0x80000000)
+  ; CHECK:   S_BRANCH %bb.1
+  bb.0:
+    liveins: $sgpr2, $sgpr3, $vgpr3
+
+    %0:sgpr_32 = COPY $sgpr2
+    undef %1.sub0:vreg_64 = COPY %0
+    undef %2.sub0:vreg_64 = COPY %0
+    S_CBRANCH_VCCNZ %bb.2, implicit undef $vcc
+    S_BRANCH %bb.4
+
+  bb.1:
+    %2:vreg_64 = COPY %3
+    S_NOP 0, implicit %2.sub0
+
+  bb.2:
+    successors: %bb.3(0x04000000), %bb.2(0x7c000000)
+
+    %3:vreg_64 = COPY %2
+    %1.sub0:vreg_64 = COPY %3.sub0
+    %2:vreg_64 = COPY %1
+    S_CBRANCH_EXECNZ %bb.2, implicit undef $exec
+    S_BRANCH %bb.3
+
+  bb.3:
+    S_BRANCH %bb.1
+
+  bb.4:
+    %3:vreg_64 = COPY %2
+    S_BRANCH %bb.1
+
+...