diff --git a/lib/Target/AMDGPU/AMDGPUISelDAGToDAG.cpp b/lib/Target/AMDGPU/AMDGPUISelDAGToDAG.cpp
index 3c8538cb03e..57caff79f16 100644
--- a/lib/Target/AMDGPU/AMDGPUISelDAGToDAG.cpp
+++ b/lib/Target/AMDGPU/AMDGPUISelDAGToDAG.cpp
@@ -67,7 +67,22 @@ class R600InstrInfo;
 
 namespace {
 
+static bool isNullConstantOrUndef(SDValue V) {
+  if (V.isUndef())
+    return true;
+
+  ConstantSDNode *Const = dyn_cast<ConstantSDNode>(V);
+  return Const != nullptr && Const->isNullValue();
+}
+
 static bool getConstantValue(SDValue N, uint32_t &Out) {
+  // This is only used for packed vectors, where ussing 0 for undef should
+  // always be good.
+  if (N.isUndef()) {
+    Out = 0;
+    return true;
+  }
+
   if (const ConstantSDNode *C = dyn_cast<ConstantSDNode>(N)) {
     Out = C->getAPIntValue().getSExtValue();
     return true;
@@ -479,7 +494,8 @@ bool AMDGPUDAGToDAGISel::isNoNanSrc(SDValue N) const {
 
 bool AMDGPUDAGToDAGISel::isInlineImmediate(const SDNode *N,
                                            bool Negated) const {
-  // TODO: Handle undef
+  if (N->isUndef())
+    return true;
 
   const SIInstrInfo *TII = Subtarget->getInstrInfo();
   if (Negated) {
diff --git a/lib/Target/AMDGPU/SIInstrInfo.td b/lib/Target/AMDGPU/SIInstrInfo.td
index ba9cd868643..c06356a685e 100644
--- a/lib/Target/AMDGPU/SIInstrInfo.td
+++ b/lib/Target/AMDGPU/SIInstrInfo.td
@@ -610,8 +610,6 @@ def getNegV2I16Imm : SDNodeXForm<build_vector, [{
   return SDValue(packNegConstantV2I16(N, *CurDAG), 0);
 }]>;
 
-
-// TODO: Handle undef as 0
 def NegSubInlineConstV216 : PatLeaf<(build_vector), [{
   assert(N->getNumOperands() == 2);
   assert(N->getOperand(0).getValueType().getSizeInBits() == 16);
@@ -620,8 +618,8 @@ def NegSubInlineConstV216 : PatLeaf<(build_vector), [{
   if (Src0 == Src1)
     return isNegInlineImmediate(Src0.getNode());
 
-  return (isNullConstant(Src0) && isNegInlineImmediate(Src1.getNode())) ||
-         (isNullConstant(Src1) && isNegInlineImmediate(Src0.getNode()));
+  return (isNullConstantOrUndef(Src0) && isNegInlineImmediate(Src1.getNode())) ||
+         (isNullConstantOrUndef(Src1) && isNegInlineImmediate(Src0.getNode()));
 }], getNegV2I16Imm>;
 
 //===----------------------------------------------------------------------===//
diff --git a/test/CodeGen/AMDGPU/shrink-add-sub-constant.ll b/test/CodeGen/AMDGPU/shrink-add-sub-constant.ll
index 478ca994fbd..163f919b8ae 100644
--- a/test/CodeGen/AMDGPU/shrink-add-sub-constant.ll
+++ b/test/CodeGen/AMDGPU/shrink-add-sub-constant.ll
@@ -1885,7 +1885,6 @@ define amdgpu_kernel void @v_test_v2i16_x_add_undef_neg32(<2 x i16> addrspace(1)
 ; GFX9:       ; %bb.0:
 ; GFX9-NEXT:    s_load_dwordx4 s[0:3], s[0:1], 0x24
 ; GFX9-NEXT:    v_lshlrev_b32_e32 v2, 2, v0
-; GFX9-NEXT:    s_mov_b32 s4, 0xffe00000
 ; GFX9-NEXT:    s_waitcnt lgkmcnt(0)
 ; GFX9-NEXT:    v_mov_b32_e32 v1, s3
 ; GFX9-NEXT:    v_add_co_u32_e32 v0, vcc, s2, v2
@@ -1895,7 +1894,7 @@ define amdgpu_kernel void @v_test_v2i16_x_add_undef_neg32(<2 x i16> addrspace(1)
 ; GFX9-NEXT:    v_mov_b32_e32 v1, s1
 ; GFX9-NEXT:    v_addc_co_u32_e32 v1, vcc, 0, v1, vcc
 ; GFX9-NEXT:    s_waitcnt vmcnt(0)
-; GFX9-NEXT:    v_pk_add_u16 v2, v3, s4
+; GFX9-NEXT:    v_pk_sub_u16 v2, v3, 32 op_sel:[0,1] op_sel_hi:[1,0]
 ; GFX9-NEXT:    global_store_dword v[0:1], v2, off
 ; GFX9-NEXT:    s_endpgm
   %tid = call i32 @llvm.amdgcn.workitem.id.x()
@@ -1947,7 +1946,6 @@ define amdgpu_kernel void @v_test_v2i16_x_add_neg32_undef(<2 x i16> addrspace(1)
 ; GFX9:       ; %bb.0:
 ; GFX9-NEXT:    s_load_dwordx4 s[0:3], s[0:1], 0x24
 ; GFX9-NEXT:    v_lshlrev_b32_e32 v2, 2, v0
-; GFX9-NEXT:    s_movk_i32 s4, 0xffe0
 ; GFX9-NEXT:    s_waitcnt lgkmcnt(0)
 ; GFX9-NEXT:    v_mov_b32_e32 v1, s3
 ; GFX9-NEXT:    v_add_co_u32_e32 v0, vcc, s2, v2
@@ -1957,7 +1955,7 @@ define amdgpu_kernel void @v_test_v2i16_x_add_neg32_undef(<2 x i16> addrspace(1)
 ; GFX9-NEXT:    v_mov_b32_e32 v1, s1
 ; GFX9-NEXT:    v_addc_co_u32_e32 v1, vcc, 0, v1, vcc
 ; GFX9-NEXT:    s_waitcnt vmcnt(0)
-; GFX9-NEXT:    v_pk_add_u16 v2, v3, s4
+; GFX9-NEXT:    v_pk_sub_u16 v2, v3, 32
 ; GFX9-NEXT:    global_store_dword v[0:1], v2, off
 ; GFX9-NEXT:    s_endpgm
   %tid = call i32 @llvm.amdgcn.workitem.id.x()