Index: lib/Target/AMDGPU/SIISelLowering.cpp
===================================================================
--- lib/Target/AMDGPU/SIISelLowering.cpp
+++ lib/Target/AMDGPU/SIISelLowering.cpp
@@ -1091,12 +1091,6 @@
   MachineBasicBlock *SplitBB
     = MF->CreateMachineBasicBlock(BB->getBasicBlock());
 
-  SmallSet<unsigned, 8> SplitDefRegs;
-  for (auto I = SplitPoint, E = BB->end(); I != E; ++I) {
-    for (MachineOperand &Def : I->defs())
-      SplitDefRegs.insert(Def.getReg());
-  }
-
   // Fix the block phi references to point to the new block for the defs in the
   // second piece of the block.
   for (MachineBasicBlock *Succ : BB->successors()) {
@@ -1104,13 +1098,10 @@
       if (!MI.isPHI())
         break;
 
-      for (unsigned I = 1, E = MI.getNumOperands(); I != E; I += 2) {
-        unsigned IncomingReg = MI.getOperand(I).getReg();
-        MachineOperand &FromBB = MI.getOperand(I + 1);
+      for (unsigned I = 2, E = MI.getNumOperands(); I != E; I += 2) {
+        MachineOperand &FromBB = MI.getOperand(I);
         if (BB == FromBB.getMBB()) {
-          if (SplitDefRegs.count(IncomingReg))
-            FromBB.setMBB(SplitBB);
-
+          FromBB.setMBB(SplitBB);
           break;
         }
       }
@@ -1120,7 +1111,6 @@
   MF->insert(++MachineFunction::iterator(BB), SplitBB);
   SplitBB->splice(SplitBB->begin(), BB, SplitPoint, BB->end());
 
-
   SplitBB->transferSuccessors(BB);
   BB->addSuccessor(SplitBB);
 
Index: test/CodeGen/AMDGPU/skip-if-dead.ll
===================================================================
--- test/CodeGen/AMDGPU/skip-if-dead.ll
+++ test/CodeGen/AMDGPU/skip-if-dead.ll
@@ -249,6 +249,54 @@
   ret void
 }
 
+; bug 28550
+; CHECK-LABEL: {{^}}phi_use_def_before_kill:
+; CHECK: v_cndmask_b32_e64 [[PHIREG:v[0-9]+]], 0, -1.0,
+; CHECK: v_cmpx_le_f32_e32 vcc, 0,
+; CHECK-NEXT: s_cbranch_execnz [[BB4:BB[0-9]+_[0-9]+]]
+
+; CHECK: exp
+; CHECK-NEXT: s_endpgm
+
+; CHECK: [[KILLBB:BB[0-9]+_[0-9]+]]:
+; CHECK: s_and_b64 vcc, exec,
+; CHECK-NEXT: s_cbranch_vccz [[PHIBB:BB[0-9]+_[0-9]+]]
+
+; CHECK: [[PHIBB]]:
+; CHECK: v_cmp_eq_f32_e32 vcc, 0, [[PHIREG]]
+; CHECK: s_and_b64 vcc, exec, vcc
+; CHECK: s_cbranch_vccz [[ENDBB:BB[0-9]+_[0-9]+]]
+
+; CHECK: ; BB#3: ; %bb10
+; CHECK: v_mov_b32_e32 v{{[0-9]+}}, 9
+; CHECK: buffer_store_dword
+
+; CHECK: [[ENDBB]]:
+; CHECK-NEXT: s_endpgm
+define amdgpu_ps void @phi_use_def_before_kill() #0 {
+bb:
+  %tmp = fadd float undef, 1.000000e+00
+  %tmp1 = fcmp olt float 0.000000e+00, %tmp
+  %tmp2 = select i1 %tmp1, float -1.000000e+00, float 0.000000e+00
+  call void @llvm.AMDGPU.kill(float %tmp2)
+  br i1 undef, label %phibb, label %bb8
+
+phibb:
+  %tmp5 = phi float [ %tmp2, %bb ], [ 4.0, %bb8 ]
+  %tmp6 = fcmp oeq float %tmp5, 0.000000e+00
+  br i1 %tmp6, label %bb10, label %end
+
+bb8:
+  store volatile i32 8, i32 addrspace(1)* undef
+  br label %phibb
+
+bb10:
+  store volatile i32 9, i32 addrspace(1)* undef
+  br label %end
+
+end:
+  ret void
+}
 
 declare void @llvm.AMDGPU.kill(float) #0