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
@@ -1212,7 +1212,10 @@
       }
       ++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 +1,309 @@
+# RUN: llc -march=amdgcn -run-pass simple-register-coalescing -verify-machineinstrs -o - %s | FileCheck %s
+#
+# CHECK-LABEL: bb.4:
+# CHECK-NOT:     COPY
+# CHECK-LABEL: bb.5:
+#
+# After some coalescing work, the copies in bb.4
+# change from:
+#     %12:vreg_512 = COPY killed %244
+#    %242:vreg_512 = COPY killed %12
+# to:
+#    %90:vreg_512 = COPY %38:vreg_512
+#
+# The failure occurs when processing this COPY in removePartialRedundency(). The
+# coalescer tries to prune and extend one of the subrange of %90 that is undef
+# from bb.0. The findReachingDef() will search all the way through one of
+# the predecessor chain: 4->27->1->0 to find the reaching-def. As we did not
+# provide the Undefs, it failed to find the reaching-def in that predecessor
+# chain and assert:
+# "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:             |
+  bb.0:
+    successors: %bb.1, %bb.2
+    liveins: $sgpr2, $sgpr3, $vgpr3
+
+    %53:vgpr_32 = COPY killed $vgpr3
+    %50:sgpr_32 = COPY killed $sgpr3
+    %49:sgpr_32 = COPY killed $sgpr2
+    %57:sreg_64 = S_GETPC_B64
+    %58:sreg_64 = COPY killed %57
+    %58.sub0:sreg_64 = COPY killed %49
+    %59:sgpr_128 = S_LOAD_DWORDX4_IMM killed %58, 0, 0, 0
+    %60:sgpr_32 = S_BUFFER_LOAD_DWORD_IMM killed %59, 1, 0, 0 :: (dereferenceable invariant load 4)
+    %63:vgpr_32 = V_MOV_B32_e32 1092616192, implicit $exec
+    %62:vgpr_32 = nnan nsz arcp contract afn reassoc nofpexcept V_MUL_F32_e32 %60, killed %63, implicit $mode, implicit $exec
+    %183:vgpr_32 = V_MOV_B32_e32 1065353216, implicit $exec
+    undef %182.sub0:vreg_512 = COPY killed %183
+    %182.sub2:vreg_512 = COPY %62
+    %182.sub3:vreg_512 = COPY %62
+    %88:sreg_64 = nofpexcept V_CMP_GT_F32_e64 0, 1065353216, 0, %53, 0, implicit $mode, implicit $exec
+    %89:sreg_64 = nofpexcept V_CMP_NGT_F32_e64 0, 1065353216, 0, %53, 0, implicit $mode, implicit $exec
+    %5:sreg_64_xexec = nofpexcept V_CMP_LT_F32_e64 0, 1065353216, 0, killed %50, 0, implicit $mode, implicit $exec
+    %92:sreg_64 = nofpexcept V_CMP_GT_F32_e64 0, 0, 0, %53, 0, implicit $mode, implicit $exec
+    %93:sreg_64 = nofpexcept V_CMP_NGT_F32_e64 0, 0, 0, killed %53, 0, implicit $mode, implicit $exec
+    %241:sreg_64 = COPY %88
+    %242:vreg_512 = COPY %182
+    %8:sreg_64 = COPY $exec, implicit-def $exec
+    %262:sreg_64 = S_AND_B64 %8, %89, implicit-def dead $scc
+    $exec = S_MOV_B64_term killed %262
+    S_CBRANCH_EXECZ %bb.2, implicit $exec
+    S_BRANCH %bb.1
+
+  bb.1:
+    %96:sreg_64 = nofpexcept V_CMP_NGT_F32_e64 0, 1065353216, 0, killed %60, 0, implicit $mode, implicit $exec
+    %94:sreg_64 = S_MOV_B64 -1
+    %98:sreg_64 = S_AND_B64 $exec, killed %96, implicit-def dead $scc
+    $vcc = COPY killed %98
+    S_CBRANCH_VCCNZ %bb.3, implicit killed $vcc
+    S_BRANCH %bb.27
+
+  bb.2:
+    successors: %bb.13, %bb.17
+
+    $exec = S_OR_B64 $exec, killed %8, implicit-def $scc
+    %9:vreg_512 = COPY killed %242
+    %10:sreg_64 = COPY killed %241
+    %11:sreg_64 = COPY $exec, implicit-def $exec
+    %263:sreg_64 = S_AND_B64 %11, killed %10, implicit-def dead $scc
+    $exec = S_MOV_B64_term killed %263
+    S_CBRANCH_EXECZ %bb.17, implicit $exec
+    S_BRANCH %bb.13
+
+  bb.3:
+    %99:sreg_64 = S_MOV_B64 0
+    %245:sreg_64 = IMPLICIT_DEF
+    %246:sreg_64 = IMPLICIT_DEF
+    %247:sreg_64 = COPY killed %99
+    %248:vreg_512 = COPY killed %182
+    S_BRANCH %bb.5
+
+  bb.4:
+    %13:sreg_64 = COPY killed %243
+    %215:sreg_64 = S_ANDN2_B64 killed %88, $exec, implicit-def dead $scc
+    %216:sreg_64 = S_AND_B64 killed %13, $exec, implicit-def dead $scc
+    %214:sreg_64 = S_OR_B64 killed %215, killed %216, implicit-def dead $scc
+    %241:sreg_64 = COPY killed %214
+    %12:vreg_512 = COPY killed %244
+    %242:vreg_512 = COPY killed %12
+    S_BRANCH %bb.2
+
+  bb.5:
+    successors: %bb.6, %bb.7
+
+    %15:vreg_512 = COPY killed %248
+    %14:sreg_64 = COPY killed %247
+    %225:sreg_64 = COPY killed %246
+    %238:sreg_64 = COPY killed %245
+    %100:sreg_64 = S_MOV_B64 -1
+    %101:vgpr_32 = V_CNDMASK_B32_e64 0, 0, 0, 1, %5, implicit $exec
+    V_CMP_NE_U32_e32 1, killed %101, implicit-def $vcc, implicit $exec
+    $vcc = S_AND_B64 $exec, killed $vcc, implicit-def dead $scc
+    %249:sreg_64 = COPY %100
+    %250:vreg_512 = COPY %15
+    S_CBRANCH_VCCNZ %bb.7, implicit killed $vcc
+    S_BRANCH %bb.6
+
+  bb.6:
+    successors: %bb.8, %bb.9
+
+    %104:sreg_64 = S_MOV_B64 0
+    %251:sreg_64 = COPY killed %104
+    %252:vreg_512 = COPY %15
+    %16:sreg_64 = COPY $exec, implicit-def $exec
+    %264:sreg_64 = S_AND_B64 %16, %93, implicit-def dead $scc
+    $exec = S_MOV_B64_term killed %264
+    S_CBRANCH_EXECZ %bb.9, implicit $exec
+    S_BRANCH %bb.8
+
+  bb.7:
+    successors: %bb.10, %bb.11
+
+    %17:vreg_512 = COPY killed %250
+    %18:sreg_64 = COPY killed %249
+    %223:sreg_64 = S_OR_B64 killed %225, $exec, implicit-def dead $scc
+    %253:sreg_64 = COPY killed %100
+    %254:sreg_64 = COPY %223
+    %19:sreg_64 = COPY $exec, implicit-def $exec
+    %265:sreg_64 = S_AND_B64 %19, killed %18, implicit-def dead $scc
+    $exec = S_MOV_B64_term killed %265
+    S_CBRANCH_EXECZ %bb.11, implicit $exec
+    S_BRANCH %bb.10
+
+  bb.8:
+    undef %175.sub0:vreg_512 = COPY %62
+    %175.sub2:vreg_512 = COPY %15.sub2
+    %175.sub3:vreg_512 = COPY %15.sub3
+    %20:vreg_512 = COPY killed %175
+    %220:sreg_64 = COPY $exec
+    %251:sreg_64 = COPY killed %220
+    %252:vreg_512 = COPY killed %20
+
+  bb.9:
+    $exec = S_OR_B64 $exec, killed %16, implicit-def $scc
+    %21:vreg_512 = COPY killed %252
+    %22:sreg_64 = COPY killed %251
+    %249:sreg_64 = COPY killed %22
+    %250:vreg_512 = COPY killed %21
+    S_BRANCH %bb.7
+
+  bb.10:
+    successors: %bb.12, %bb.25
+
+    %131:sreg_64 = S_MOV_B64 -1
+    %261:sreg_64 = COPY killed %131
+    %23:sreg_64 = COPY $exec, implicit-def $exec
+    %266:sreg_64 = S_AND_B64 %23, %93, implicit-def dead $scc
+    $exec = S_MOV_B64_term killed %266
+    S_CBRANCH_EXECZ %bb.25, implicit $exec
+    S_BRANCH %bb.12
+
+  bb.11:
+    successors: %bb.26(0x04000000), %bb.5(0x7c000000)
+
+    $exec = S_OR_B64 $exec, killed %19, implicit-def $scc
+    %24:sreg_64 = COPY killed %254
+    %25:sreg_64 = COPY killed %253
+    %271:sreg_64 = S_AND_B64 $exec, killed %25, implicit-def $scc
+    %26:sreg_64 = S_OR_B64 %271, killed %14, implicit-def $scc
+    %239:sreg_64 = S_ANDN2_B64 killed %238, $exec, implicit-def dead $scc
+    %240:sreg_64 = S_AND_B64 %24, $exec, implicit-def dead $scc
+    %44:sreg_64 = S_OR_B64 killed %239, killed %240, implicit-def dead $scc
+    %245:sreg_64 = COPY %44
+    %246:sreg_64 = COPY killed %24
+    %247:sreg_64 = COPY %26
+    %248:vreg_512 = COPY killed %17
+    $exec = S_ANDN2_B64_term $exec, %26, implicit-def $scc
+    S_CBRANCH_EXECNZ %bb.5, implicit $exec
+    S_BRANCH %bb.26
+
+  bb.12:
+    %234:sreg_64 = S_XOR_B64 $exec, -1, implicit-def dead $scc
+    %261:sreg_64 = COPY killed %234
+    S_BRANCH %bb.25
+
+  bb.13:
+    successors: %bb.14, %bb.18
+
+    %137:sreg_64 = S_MOV_B64 -1
+    %255:sreg_64 = COPY killed %137
+    %256:vreg_512 = COPY %9
+    %27:sreg_64 = COPY $exec, implicit-def $exec
+    %267:sreg_64 = S_AND_B64 %27, %89, implicit-def dead $scc
+    $exec = S_MOV_B64_term killed %267
+    S_CBRANCH_EXECZ %bb.18, implicit $exec
+    S_BRANCH %bb.14
+
+  bb.14:
+    successors: %bb.19, %bb.20
+
+    %139:sreg_64 = S_MOV_B64 0
+    %257:sreg_64 = COPY killed %139
+    %258:vreg_512 = COPY %9
+    %28:sreg_64 = COPY $exec, implicit-def $exec
+    %268:sreg_64 = S_AND_B64 %28, killed %93, implicit-def dead $scc
+    $exec = S_MOV_B64_term killed %268
+    S_CBRANCH_EXECZ %bb.20, implicit $exec
+    S_BRANCH %bb.19
+
+  bb.15:
+    S_BRANCH %bb.23
+
+  bb.16:
+
+  bb.17:
+    $exec = S_OR_B64 $exec, killed %11, implicit-def $scc
+    %168:vgpr_32 = V_MOV_B32_e32 0, implicit $exec
+    EXP_DONE 0, killed %168, undef %170:vgpr_32, undef %172:vgpr_32, undef %174:vgpr_32, -1, 0, 1, implicit $exec
+    S_ENDPGM 0
+
+  bb.18:
+    successors: %bb.21, %bb.16
+
+    $exec = S_OR_B64 $exec, killed %27, implicit-def $scc
+    %30:vreg_512 = COPY killed %256
+    %31:sreg_64 = COPY killed %255
+    %32:sreg_64 = COPY $exec, implicit-def $exec
+    %269:sreg_64 = S_AND_B64 %32, killed %31, implicit-def dead $scc
+    $exec = S_MOV_B64_term killed %269
+    S_CBRANCH_EXECZ %bb.16, implicit $exec
+    S_BRANCH %bb.21
+
+  bb.19:
+    undef %203.sub0:vreg_512 = COPY %9.sub2
+    %203.sub3:vreg_512 = COPY %9.sub3
+    %33:vreg_512 = COPY killed %203
+    %232:sreg_64 = COPY $exec
+    %257:sreg_64 = COPY killed %232
+    %258:vreg_512 = COPY killed %33
+
+  bb.20:
+    $exec = S_OR_B64 $exec, killed %28, implicit-def $scc
+    %34:vreg_512 = COPY killed %258
+    %35:sreg_64 = COPY killed %257
+    %230:sreg_64 = S_ORN2_B64 killed %35, $exec, implicit-def dead $scc
+    %255:sreg_64 = COPY killed %230
+    %256:vreg_512 = COPY killed %34
+    S_BRANCH %bb.18
+
+  bb.21:
+    successors: %bb.22, %bb.23
+
+    %36:sreg_64 = COPY $exec, implicit-def $exec
+    %270:sreg_64 = S_AND_B64 %36, killed %89, implicit-def dead $scc
+    $exec = S_MOV_B64_term killed %270
+    S_CBRANCH_EXECZ %bb.23, implicit $exec
+    S_BRANCH %bb.22
+
+  bb.22:
+    %38:vgpr_32 = COPY %30.sub0
+    %166:sreg_64 = S_MOV_B64 0
+    %259:sreg_64 = COPY killed %166
+    %260:vgpr_32 = COPY killed %38
+    S_BRANCH %bb.24
+
+  bb.23:
+    S_BRANCH %bb.16
+
+  bb.24:
+    successors: %bb.15(0x04000000), %bb.24(0x7c000000)
+
+    %39:sreg_64 = COPY killed %259
+    %272:sreg_64 = S_AND_B64 $exec, %92, implicit-def $scc
+    %41:sreg_64 = S_OR_B64 %272, killed %39, implicit-def $scc
+    %40:vgpr_32 = COPY killed %260
+    %42:vgpr_32 = V_CNDMASK_B32_e64 0, killed %40, 0, %30.sub3, %5, implicit $exec
+    %259:sreg_64 = COPY %41
+    %260:vgpr_32 = COPY killed %42
+    $exec = S_ANDN2_B64_term $exec, %41, implicit-def $scc
+    S_CBRANCH_EXECNZ %bb.24, implicit $exec
+    S_BRANCH %bb.15
+
+  bb.25:
+    $exec = S_OR_B64 $exec, killed %23, implicit-def $scc
+    %43:sreg_64 = COPY killed %261
+    %227:sreg_64 = S_ANDN2_B64 killed %223, $exec, implicit-def dead $scc
+    %224:sreg_64 = COPY killed %227
+    %228:sreg_64 = S_ORN2_B64 killed %43, $exec, implicit-def dead $scc
+    %253:sreg_64 = COPY killed %228
+    %254:sreg_64 = COPY killed %224
+    S_BRANCH %bb.11
+
+  bb.26:
+    $exec = S_OR_B64 $exec, killed %26, implicit-def $scc
+    %243:sreg_64 = COPY killed %44
+    %244:vreg_512 = COPY killed %15
+    S_BRANCH %bb.4
+
+  bb.27:
+    %243:sreg_64 = COPY killed %94
+    %244:vreg_512 = COPY killed %182
+    S_BRANCH %bb.4
+
+...