Index: lib/CodeGen/RegisterCoalescer.cpp
===================================================================
--- lib/CodeGen/RegisterCoalescer.cpp
+++ lib/CodeGen/RegisterCoalescer.cpp
@@ -2071,7 +2071,7 @@
   LaneBitmask computeWriteLanes(const MachineInstr *DefMI, bool &Redef) const;
 
   /// Find the ultimate value that VNI was copied from.
-  std::pair<const VNInfo*,unsigned> followCopyChain(const VNInfo *VNI) const;
+  std::pair<const VNInfo*,unsigned> followCopyChain(const VNInfo *VNI, bool &SubRangeDead) const;
 
   bool valuesIdentical(VNInfo *Val0, VNInfo *Val1, const JoinVals &Other) const;
 
@@ -2190,8 +2190,9 @@
 }
 
 std::pair<const VNInfo*, unsigned> JoinVals::followCopyChain(
-    const VNInfo *VNI) const {
+  const VNInfo *VNI, bool &SubRangeDead) const {
   unsigned Reg = this->Reg;
+  SubRangeDead = false;
 
   while (!VNI->isPHIDef()) {
     SlotIndex Def = VNI->def;
@@ -2222,6 +2223,13 @@
         break;
       }
     }
+    if (ValueIn == nullptr && SubIdx == 0) {
+      // Didn't match a subrange so it must actually be dead
+      // Set the flag and let the caller deal with this scenario
+      //llvm_unreachable("Found a dead subrange");
+      SubRangeDead = true;
+      break;
+    }
     if (ValueIn == nullptr)
       break;
     VNI = ValueIn;
@@ -2234,19 +2242,20 @@
                                const JoinVals &Other) const {
   const VNInfo *Orig0;
   unsigned Reg0;
-  std::tie(Orig0, Reg0) = followCopyChain(Value0);
-  if (Orig0 == Value1)
+  bool SubRangeDead = false;
+  std::tie(Orig0, Reg0) = followCopyChain(Value0, SubRangeDead);
+  if (Orig0 == Value1 || SubRangeDead)
     return true;
 
   const VNInfo *Orig1;
   unsigned Reg1;
-  std::tie(Orig1, Reg1) = Other.followCopyChain(Value1);
+  std::tie(Orig1, Reg1) = Other.followCopyChain(Value1, SubRangeDead);
 
   // The values are equal if they are defined at the same place and use the
   // same register. Note that we cannot compare VNInfos directly as some of
   // them might be from a copy created in mergeSubRangeInto()  while the other
   // is from the original LiveInterval.
-  return Orig0->def == Orig1->def && Reg0 == Reg1;
+  return (Orig0->def == Orig1->def && Reg0 == Reg1) || SubRangeDead;
 }
 
 JoinVals::ConflictResolution
Index: test/CodeGen/AMDGPU/regcoalesce-subregjoin-fullcopy.mir
===================================================================
--- /dev/null
+++ test/CodeGen/AMDGPU/regcoalesce-subregjoin-fullcopy.mir
@@ -0,0 +1,362 @@
+# RUN: llc -march=amdgcn -run-pass simple-register-coalescing -verify-machineinstrs -o - %s | FileCheck --check-prefix=GCN %s
+#
+# See bug http://llvm.org/PR33152 for details of the bug this test is checking
+# for.
+# This test will provoke a subrange join during simple register
+# coalescing. Withough a fix for PR33152 this causes an unreachable in SubRange
+# Join
+#
+# The lines where the problem exhibits are the last 2 copy instructions in the
+# BB (bb.25)
+#
+# GCN-LABEL: bb.10:
+# GCN: successors: %bb.11(0x{{[0-9]+}}), %bb.22(0x{{[0-9]+}})
+# GCN: %{{[0-9]+}}:vreg_128 = BUFFER_LOAD_DWORDX4_OFFSET %{{[0-9]+}}, 0, 0, 0, 0, 0, implicit %exec
+#
+
+--- |
+  ; Function Attrs: nounwind
+  define amdgpu_ps void @main() local_unnamed_addr #0 {
+    ret void
+  }
+
+...
+---
+name:            main
+alignment:       0
+exposesReturnsTwice: false
+legalized:       false
+regBankSelected: false
+selected:        false
+tracksRegLiveness: true
+registers:
+  - { id: 0, class: sreg_128, preferred-register: '' }
+  - { id: 1, class: sreg_64, preferred-register: '' }
+  - { id: 2, class: sreg_128, preferred-register: '' }
+  - { id: 3, class: sreg_128, preferred-register: '' }
+  - { id: 4, class: sreg_128, preferred-register: '' }
+  - { id: 5, class: sreg_64, preferred-register: '' }
+  - { id: 6, class: sreg_64, preferred-register: '' }
+  - { id: 7, class: sreg_128, preferred-register: '' }
+  - { id: 8, class: sreg_128, preferred-register: '' }
+  - { id: 9, class: sreg_128, preferred-register: '' }
+  - { id: 10, class: sreg_64, preferred-register: '' }
+  - { id: 11, class: sreg_128, preferred-register: '' }
+  - { id: 12, class: sreg_128, preferred-register: '' }
+  - { id: 13, class: sreg_128, preferred-register: '' }
+  - { id: 14, class: sreg_128, preferred-register: '' }
+  - { id: 15, class: sreg_128, preferred-register: '' }
+  - { id: 16, class: sreg_128, preferred-register: '' }
+  - { id: 17, class: sreg_128, preferred-register: '' }
+  - { id: 18, class: sreg_128, preferred-register: '' }
+  - { id: 19, class: sreg_128, preferred-register: '' }
+  - { id: 20, class: sreg_128, preferred-register: '' }
+  - { id: 21, class: sreg_64, preferred-register: '' }
+  - { id: 22, class: sreg_128, preferred-register: '' }
+  - { id: 23, class: sreg_128, preferred-register: '' }
+  - { id: 24, class: sreg_64, preferred-register: '' }
+  - { id: 25, class: sreg_128, preferred-register: '' }
+  - { id: 26, class: sreg_128, preferred-register: '' }
+  - { id: 27, class: sreg_64, preferred-register: '' }
+  - { id: 28, class: sreg_32_xm0, preferred-register: '' }
+  - { id: 29, class: sreg_64, preferred-register: '' }
+  - { id: 30, class: sreg_32_xm0, preferred-register: '' }
+  - { id: 31, class: sreg_32_xm0, preferred-register: '' }
+  - { id: 32, class: sreg_32_xm0, preferred-register: '' }
+  - { id: 33, class: sreg_128, preferred-register: '' }
+  - { id: 34, class: vreg_128, preferred-register: '' }
+  - { id: 35, class: sreg_32_xm0, preferred-register: '' }
+  - { id: 36, class: sreg_32_xm0, preferred-register: '' }
+  - { id: 37, class: sreg_32_xm0, preferred-register: '' }
+  - { id: 38, class: sreg_32_xm0, preferred-register: '' }
+  - { id: 39, class: sreg_128, preferred-register: '' }
+  - { id: 40, class: vgpr_32, preferred-register: '' }
+  - { id: 41, class: sreg_64, preferred-register: '%vcc' }
+  - { id: 42, class: vgpr_32, preferred-register: '' }
+  - { id: 43, class: vgpr_32, preferred-register: '' }
+  - { id: 44, class: vgpr_32, preferred-register: '' }
+  - { id: 45, class: sreg_64, preferred-register: '%vcc' }
+  - { id: 46, class: sreg_64, preferred-register: '' }
+  - { id: 47, class: sreg_32_xm0, preferred-register: '' }
+  - { id: 48, class: vgpr_32, preferred-register: '' }
+  - { id: 49, class: vgpr_32, preferred-register: '' }
+  - { id: 50, class: vgpr_32, preferred-register: '' }
+  - { id: 51, class: vgpr_32, preferred-register: '' }
+  - { id: 52, class: sreg_32_xm0, preferred-register: '' }
+  - { id: 53, class: vgpr_32, preferred-register: '' }
+  - { id: 54, class: sreg_32_xm0, preferred-register: '' }
+  - { id: 55, class: sreg_32_xm0, preferred-register: '' }
+  - { id: 56, class: sreg_128, preferred-register: '' }
+  - { id: 57, class: sreg_32_xm0, preferred-register: '' }
+  - { id: 58, class: sreg_32_xm0, preferred-register: '' }
+  - { id: 59, class: sreg_32_xm0, preferred-register: '' }
+  - { id: 60, class: sreg_128, preferred-register: '' }
+  - { id: 61, class: sreg_32_xm0, preferred-register: '' }
+  - { id: 62, class: sreg_32_xm0, preferred-register: '' }
+  - { id: 63, class: vgpr_32, preferred-register: '' }
+  - { id: 64, class: sreg_64, preferred-register: '%vcc' }
+  - { id: 65, class: vgpr_32, preferred-register: '' }
+  - { id: 66, class: vgpr_32, preferred-register: '' }
+  - { id: 67, class: vgpr_32, preferred-register: '' }
+  - { id: 68, class: vgpr_32, preferred-register: '' }
+  - { id: 69, class: vgpr_32, preferred-register: '' }
+  - { id: 70, class: sreg_64, preferred-register: '%vcc' }
+  - { id: 71, class: sreg_64, preferred-register: '' }
+  - { id: 72, class: sreg_128, preferred-register: '' }
+  - { id: 73, class: sreg_32_xm0, preferred-register: '' }
+  - { id: 74, class: vgpr_32, preferred-register: '' }
+  - { id: 75, class: vgpr_32, preferred-register: '' }
+  - { id: 76, class: vgpr_32, preferred-register: '' }
+  - { id: 77, class: vgpr_32, preferred-register: '' }
+  - { id: 78, class: sreg_128, preferred-register: '' }
+  - { id: 79, class: sreg_128, preferred-register: '' }
+  - { id: 80, class: sreg_32_xm0, preferred-register: '' }
+  - { id: 81, class: vgpr_32, preferred-register: '' }
+  - { id: 82, class: vgpr_32, preferred-register: '' }
+  - { id: 83, class: vgpr_32, preferred-register: '' }
+  - { id: 84, class: vgpr_32, preferred-register: '' }
+  - { id: 85, class: vgpr_32, preferred-register: '' }
+  - { id: 86, class: vgpr_32, preferred-register: '' }
+  - { id: 87, class: vgpr_32, preferred-register: '' }
+  - { id: 88, class: vgpr_32, preferred-register: '' }
+  - { id: 89, class: vgpr_32, preferred-register: '' }
+  - { id: 90, class: vgpr_32, preferred-register: '' }
+  - { id: 91, class: vgpr_32, preferred-register: '' }
+  - { id: 92, class: vgpr_32, preferred-register: '' }
+  - { id: 93, class: vgpr_32, preferred-register: '' }
+  - { id: 94, class: vgpr_32, preferred-register: '' }
+  - { id: 95, class: sreg_128, preferred-register: '' }
+  - { id: 96, class: vgpr_32, preferred-register: '' }
+  - { id: 97, class: vgpr_32, preferred-register: '' }
+  - { id: 98, class: vgpr_32, preferred-register: '' }
+  - { id: 99, class: vgpr_32, preferred-register: '' }
+  - { id: 100, class: vgpr_32, preferred-register: '' }
+  - { id: 101, class: vgpr_32, preferred-register: '' }
+  - { id: 102, class: vreg_128, preferred-register: '' }
+  - { id: 103, class: vreg_128, preferred-register: '' }
+  - { id: 104, class: vreg_128, preferred-register: '' }
+  - { id: 105, class: vreg_128, preferred-register: '' }
+  - { id: 106, class: vreg_128, preferred-register: '' }
+  - { id: 107, class: vreg_128, preferred-register: '' }
+  - { id: 108, class: vreg_128, preferred-register: '' }
+  - { id: 109, class: vgpr_32, preferred-register: '' }
+  - { id: 110, class: vreg_128, preferred-register: '' }
+  - { id: 111, class: vreg_128, preferred-register: '' }
+  - { id: 112, class: vreg_128, preferred-register: '' }
+  - { id: 113, class: vgpr_32, preferred-register: '' }
+  - { id: 114, class: vreg_128, preferred-register: '' }
+  - { id: 115, class: vgpr_32, preferred-register: '' }
+  - { id: 116, class: vreg_128, preferred-register: '' }
+  - { id: 117, class: vreg_128, preferred-register: '' }
+  - { id: 118, class: vgpr_32, preferred-register: '' }
+  - { id: 119, class: vreg_128, preferred-register: '' }
+  - { id: 120, class: vreg_128, preferred-register: '' }
+  - { id: 121, class: vreg_128, preferred-register: '' }
+  - { id: 122, class: vgpr_32, preferred-register: '' }
+  - { id: 123, class: vgpr_32, preferred-register: '' }
+  - { id: 124, class: vreg_128, preferred-register: '' }
+  - { id: 125, class: vgpr_32, preferred-register: '' }
+  - { id: 126, class: vgpr_32, preferred-register: '' }
+  - { id: 127, class: vgpr_32, preferred-register: '' }
+  - { id: 128, class: vgpr_32, preferred-register: '' }
+  - { id: 129, class: vreg_128, preferred-register: '' }
+  - { id: 130, class: vgpr_32, preferred-register: '' }
+  - { id: 131, class: vgpr_32, preferred-register: '' }
+  - { id: 132, class: vgpr_32, preferred-register: '' }
+  - { id: 133, class: vreg_128, preferred-register: '' }
+  - { id: 134, class: vreg_128, preferred-register: '' }
+  - { id: 135, class: vreg_128, preferred-register: '' }
+  - { id: 136, class: vgpr_32, preferred-register: '' }
+  - { id: 137, class: vgpr_32, preferred-register: '' }
+  - { id: 138, class: vgpr_32, preferred-register: '' }
+  - { id: 139, class: vgpr_32, preferred-register: '' }
+  - { id: 140, class: vgpr_32, preferred-register: '' }
+  - { id: 141, class: vreg_128, preferred-register: '' }
+  - { id: 142, class: vreg_128, preferred-register: '' }
+  - { id: 143, class: vreg_128, preferred-register: '' }
+  - { id: 144, class: vgpr_32, preferred-register: '' }
+  - { id: 145, class: vreg_128, preferred-register: '' }
+  - { id: 146, class: vreg_128, preferred-register: '' }
+  - { id: 147, class: vreg_128, preferred-register: '' }
+  - { id: 148, class: vreg_128, preferred-register: '' }
+  - { id: 149, class: sreg_128, preferred-register: '' }
+  - { id: 150, class: vreg_128, preferred-register: '' }
+  - { id: 151, class: sreg_64, preferred-register: '' }
+  - { id: 152, class: vreg_128, preferred-register: '' }
+  - { id: 153, class: sreg_64, preferred-register: '' }
+  - { id: 154, class: vreg_128, preferred-register: '' }
+  - { id: 155, class: vreg_128, preferred-register: '' }
+  - { id: 156, class: vreg_128, preferred-register: '' }
+  - { id: 157, class: vreg_128, preferred-register: '' }
+  - { id: 158, class: vreg_128, preferred-register: '' }
+  - { id: 159, class: sreg_64, preferred-register: '' }
+  - { id: 160, class: sreg_64, preferred-register: '' }
+  - { id: 161, class: sreg_128, preferred-register: ''}
+  - { id: 162, class: sreg_32, preferred-register: ''}
+liveins:
+frameInfo:
+  isFrameAddressTaken: false
+  isReturnAddressTaken: false
+  hasStackMap:     false
+  hasPatchPoint:   false
+  stackSize:       0
+  offsetAdjustment: 0
+  maxAlignment:    0
+  adjustsStack:    false
+  hasCalls:        false
+  stackProtector:  ''
+  maxCallFrameSize: 4294967295
+  hasOpaqueSPAdjustment: false
+  hasVAStart:      false
+  hasMustTailInVarArgFunc: false
+  savePoint:       ''
+  restorePoint:    ''
+fixedStack:
+stack:
+constants:
+body:             |
+  bb.0:
+    S_CBRANCH_SCC1 %bb.3, implicit undef %scc
+    S_BRANCH %bb.1
+
+  bb.1:
+    S_CBRANCH_SCC1 %bb.3, implicit undef %scc
+    S_BRANCH %bb.3
+
+  bb.3:
+    S_CBRANCH_SCC1 %bb.6, implicit undef %scc
+    S_BRANCH %bb.4
+
+  bb.4:
+    S_CBRANCH_SCC1 %bb.6, implicit undef %scc
+    S_BRANCH %bb.6
+
+  bb.6:
+    S_CBRANCH_SCC0 %bb.8, implicit undef %scc
+
+  bb.7:
+    %156 = IMPLICIT_DEF
+    S_BRANCH %bb.15
+
+  bb.8:
+    S_CBRANCH_SCC0 %bb.10, implicit undef %scc
+
+  bb.9:
+    %150 = IMPLICIT_DEF
+    S_BRANCH %bb.11
+
+  bb.10:
+    %24 = S_MOV_B64 0
+    %31 = S_MOV_B32 61440
+    %32 = S_MOV_B32 -1
+    %151 = COPY killed %24
+    %152 = IMPLICIT_DEF
+    S_BRANCH %bb.12
+
+  bb.11:
+    %102 = COPY killed %150
+    %148 = COPY killed %102
+    %156 = COPY killed %148
+    S_BRANCH %bb.15
+
+  bb.12:
+    %119 = COPY killed %152
+    %1 = COPY killed %151
+    undef %33.sub2 = COPY %32
+    %33.sub3 = COPY %31
+    %34 = BUFFER_LOAD_DWORDX4_OFFSET killed %33, 0, 0, 0, 0, 0, implicit %exec
+    undef %124.sub1 = COPY %119.sub1
+    %124.sub2 = COPY %119.sub2
+    %41 = V_CMP_GT_F32_e64 0, target-flags(amdgpu-rel32-lo) 0, 0, killed %34.sub3, 0, implicit %exec
+    %43 = V_ADD_F32_e32 1065353216, undef %44, implicit %exec
+    %45 = V_CMP_GT_F32_e64 0, 0, 0, killed %43, 0, implicit %exec
+    %46 = S_AND_B64 killed %45, killed %41, implicit-def dead %scc
+    %153 = COPY %1
+    %154 = COPY %124
+    %155 = IMPLICIT_DEF
+    %159 = COPY %exec, implicit-def %exec
+    %160 = S_AND_B64 %159, %46, implicit-def dead %scc
+    %5 = S_XOR_B64 %160, %159, implicit-def dead %scc
+    %exec = S_MOV_B64_term killed %160
+    SI_MASK_BRANCH %bb.13, implicit %exec
+    S_BRANCH %bb.25
+
+  bb.13:
+    %exec = S_OR_B64 %exec, %5, implicit-def %scc
+    %133 = COPY killed %155
+    %135 = COPY killed %154
+    %6 = COPY killed %153
+    %10 = S_OR_B64 %5, killed %6, implicit-def dead %scc
+    %151 = COPY %10
+    %152 = COPY killed %133
+    %exec = S_ANDN2_B64_term %exec, %10
+    S_CBRANCH_EXECNZ %bb.12, implicit %exec
+    S_BRANCH %bb.14
+
+  bb.14:
+    %exec = S_OR_B64 %exec, killed %10, implicit-def %scc
+    %104 = COPY killed %135
+    %150 = COPY killed %104
+    S_BRANCH %bb.11
+
+  bb.15:
+    %106 = COPY killed %156
+    S_BRANCH %bb.16
+
+  bb.16:
+    S_CBRANCH_SCC0 %bb.18, implicit undef %scc
+
+  bb.17:
+    %157 = IMPLICIT_DEF
+    S_BRANCH %bb.21
+
+  bb.18:
+    S_CBRANCH_SCC1 %bb.20, implicit undef %scc
+    S_BRANCH %bb.20
+
+  bb.20:
+    %74 = V_MUL_F32_e32 undef %75, killed %106.sub1, implicit %exec
+    %76 = V_MUL_F32_e32 undef %77, killed %74, implicit %exec
+    undef %141.sub0 = COPY %76
+    %157 = COPY killed %141
+
+  bb.21:
+    %142 = COPY killed %157
+    S_CBRANCH_SCC0 %bb.23, implicit undef %scc
+
+  bb.22:
+    %158 = IMPLICIT_DEF
+    S_BRANCH %bb.24
+
+  bb.23:
+    %81 = V_FMA_F32 0, undef %82, 0, killed %142.sub0, 0, undef %83, 0, 0, implicit %exec
+    %84 = V_FMA_F32 0, undef %85, 0, undef %86, 0, killed %81, 0, 0, implicit %exec
+    %87 = V_FMA_F32 0, undef %88, 0, undef %89, 0, killed %84, 0, 0, implicit %exec
+    dead %90 = V_MUL_F32_e32 undef %91, killed %87, implicit %exec
+    %92 = V_MUL_F32_e32 undef %94, undef %93, implicit %exec
+    undef %145.sub1 = COPY %92
+    %158 = COPY killed %145
+
+  bb.24:
+    %146 = COPY killed %158
+    %98 = V_FMA_F32 0, killed %146.sub1, 0, target-flags(amdgpu-gotprel32-lo) 1056964608, 0, 1056964608, 0, 0, implicit %exec
+    EXP 1, undef %99, killed %98, undef %100, undef %101, -1, 0, 15, implicit %exec
+    S_ENDPGM
+
+  bb.25:
+    dead %48 = V_FMA_F32 0, killed %119.sub2, 0, undef %49, 0, undef %50, 0, 0, implicit %exec
+    dead %51 = BUFFER_LOAD_DWORD_OFFEN undef %53, undef %161, undef %162, 0, 0, 0, 0, implicit %exec
+    undef %129.sub1 = COPY %124.sub1
+    %129.sub2 = COPY %124.sub2
+    %64 = V_CMP_NGT_F32_e64 0, 0, 0, undef %65, 0, implicit %exec
+    %67 = V_ADD_F32_e32 1065353216, undef %68, implicit %exec
+    %69 = V_ADD_F32_e32 1065353216, killed %67, implicit %exec
+    %70 = V_CMP_NGT_F32_e64 0, 0, 0, killed %69, 0, implicit %exec
+    %71 = S_OR_B64 killed %70, killed %64, implicit-def dead %scc
+    %21 = S_OR_B64 killed %71, killed %1, implicit-def dead %scc
+    %153 = COPY killed %21
+    %154 = COPY %129
+    %155 = COPY killed %129
+    S_BRANCH %bb.13
+
+...