diff --git a/llvm/lib/Analysis/InstructionSimplify.cpp b/llvm/lib/Analysis/InstructionSimplify.cpp
--- a/llvm/lib/Analysis/InstructionSimplify.cpp
+++ b/llvm/lib/Analysis/InstructionSimplify.cpp
@@ -4401,10 +4401,10 @@
   if (Q.isUndefValue(Idx))
     return PoisonValue::get(Vec->getType());
 
-  // If the scalar is undef, and there is no risk of propagating poison from the
-  // vector value, simplify to the vector value.
-  if (Q.isUndefValue(Val) &&
-      isGuaranteedNotToBeUndefOrPoison(Vec))
+  // If the scalar is poison, or it is undef and there is no risk of
+  // propagating poison from the vector value, simplify to the vector value.
+  if (isa<PoisonValue>(Val) ||
+      (Q.isUndefValue(Val) && isGuaranteedNotToBePoison(Vec)))
     return Vec;
 
   // If we are extracting a value from a vector, then inserting it into the same
diff --git a/llvm/lib/IR/Constants.cpp b/llvm/lib/IR/Constants.cpp
--- a/llvm/lib/IR/Constants.cpp
+++ b/llvm/lib/IR/Constants.cpp
@@ -1339,17 +1339,20 @@
   Constant *C = V[0];
   bool isZero = C->isNullValue();
   bool isUndef = isa<UndefValue>(C);
+  bool isPoison = isa<PoisonValue>(C);
 
   if (isZero || isUndef) {
     for (unsigned i = 1, e = V.size(); i != e; ++i)
       if (V[i] != C) {
-        isZero = isUndef = false;
+        isZero = isUndef = isPoison = false;
         break;
       }
   }
 
   if (isZero)
     return ConstantAggregateZero::get(T);
+  if (isPoison)
+    return PoisonValue::get(T);
   if (isUndef)
     return UndefValue::get(T);
 
diff --git a/llvm/test/Transforms/InstCombine/X86/x86-pack-inseltpoison.ll b/llvm/test/Transforms/InstCombine/X86/x86-pack-inseltpoison.ll
--- a/llvm/test/Transforms/InstCombine/X86/x86-pack-inseltpoison.ll
+++ b/llvm/test/Transforms/InstCombine/X86/x86-pack-inseltpoison.ll
@@ -244,7 +244,7 @@
 
 define <16 x i8> @elts_packuswb_128(<8 x i16> %a0, <8 x i16> %a1) {
 ; CHECK-LABEL: @elts_packuswb_128(
-; CHECK-NEXT:    ret <16 x i8> undef
+; CHECK-NEXT:    ret <16 x i8> poison
 ;
   %1 = insertelement <8 x i16> poison, i16 0, i32 0
   %2 = insertelement <8 x i16> poison, i16 0, i32 0
@@ -293,7 +293,7 @@
 
 define <32 x i8> @elts_packuswb_256(<16 x i16> %a0, <16 x i16> %a1) {
 ; CHECK-LABEL: @elts_packuswb_256(
-; CHECK-NEXT:    ret <32 x i8> undef
+; CHECK-NEXT:    ret <32 x i8> poison
 ;
   %1 = insertelement <16 x i16> poison, i16 0, i32 1
   %2 = insertelement <16 x i16> poison, i16 0, i32 0
@@ -344,7 +344,7 @@
 
 define <64 x i8> @elts_packuswb_512(<32 x i16> %a0, <32 x i16> %a1) {
 ; CHECK-LABEL: @elts_packuswb_512(
-; CHECK-NEXT:    ret <64 x i8> undef
+; CHECK-NEXT:    ret <64 x i8> poison
 ;
   %1 = insertelement <32 x i16> poison, i16 0, i32 1
   %2 = insertelement <32 x i16> poison, i16 0, i32 0
diff --git a/llvm/test/Transforms/InstCombine/extractelement-inseltpoison.ll b/llvm/test/Transforms/InstCombine/extractelement-inseltpoison.ll
--- a/llvm/test/Transforms/InstCombine/extractelement-inseltpoison.ll
+++ b/llvm/test/Transforms/InstCombine/extractelement-inseltpoison.ll
@@ -319,8 +319,7 @@
 ; ANY-NEXT:    [[T4:%.*]] = shufflevector <4 x double> [[B:%.*]], <4 x double> [[TMP1]], <4 x i32> <i32 undef, i32 1, i32 4, i32 3>
 ; ANY-NEXT:    [[E:%.*]] = extractelement <4 x double> [[B]], i32 1
 ; ANY-NEXT:    store double [[E]], double* [[P:%.*]], align 8
-; ANY-NEXT:    [[R:%.*]] = insertelement <4 x double> [[T4]], double poison, i64 0
-; ANY-NEXT:    ret <4 x double> [[R]]
+; ANY-NEXT:    ret <4 x double> [[T4]]
 ;
   %t3 = extractelement <2 x double> %a, i32 0
   %t4 = insertelement <4 x double> %b, double %t3, i32 2
diff --git a/llvm/test/Transforms/InstCombine/extractelement.ll b/llvm/test/Transforms/InstCombine/extractelement.ll
--- a/llvm/test/Transforms/InstCombine/extractelement.ll
+++ b/llvm/test/Transforms/InstCombine/extractelement.ll
@@ -319,8 +319,7 @@
 ; ANY-NEXT:    [[T4:%.*]] = shufflevector <4 x double> [[B:%.*]], <4 x double> [[TMP1]], <4 x i32> <i32 undef, i32 1, i32 4, i32 3>
 ; ANY-NEXT:    [[E:%.*]] = extractelement <4 x double> [[B]], i32 1
 ; ANY-NEXT:    store double [[E]], double* [[P:%.*]], align 8
-; ANY-NEXT:    [[R:%.*]] = insertelement <4 x double> [[T4]], double poison, i64 0
-; ANY-NEXT:    ret <4 x double> [[R]]
+; ANY-NEXT:    ret <4 x double> [[T4]]
 ;
   %t3 = extractelement <2 x double> %a, i32 0
   %t4 = insertelement <4 x double> %b, double %t3, i32 2
diff --git a/llvm/test/Transforms/InstSimplify/insertelement.ll b/llvm/test/Transforms/InstSimplify/insertelement.ll
--- a/llvm/test/Transforms/InstSimplify/insertelement.ll
+++ b/llvm/test/Transforms/InstSimplify/insertelement.ll
@@ -52,8 +52,7 @@
 
 define <4 x i32> @elem_poison(<4 x i32> %A) {
 ; CHECK-LABEL: @elem_poison(
-; CHECK-NEXT:    [[B:%.*]] = insertelement <4 x i32> [[A:%.*]], i32 poison, i32 1
-; CHECK-NEXT:    ret <4 x i32> [[B]]
+; CHECK-NEXT:    ret <4 x i32> [[A:%.*]]
 ;
   %B = insertelement <4 x i32> %A, i32 poison, i32 1
   ret <4 x i32> %B
diff --git a/llvm/test/Transforms/PhaseOrdering/X86/scalarization.ll b/llvm/test/Transforms/PhaseOrdering/X86/scalarization.ll
--- a/llvm/test/Transforms/PhaseOrdering/X86/scalarization.ll
+++ b/llvm/test/Transforms/PhaseOrdering/X86/scalarization.ll
@@ -27,7 +27,7 @@
 ; CHECK-NEXT:    [[DOTSCALAR6:%.*]] = add i32 [[DOTSCALAR5]], [[DIV9]]
 ; CHECK-NEXT:    [[DOTSCALAR7:%.*]] = add i32 [[DOTSCALAR6]], [[MUL21]]
 ; CHECK-NEXT:    [[DOTSCALAR8:%.*]] = add i32 [[DOTSCALAR7]], 317425
-; CHECK-NEXT:    [[TMP1:%.*]] = insertelement <4 x i32> undef, i32 [[DOTSCALAR8]], i64 0
+; CHECK-NEXT:    [[TMP1:%.*]] = insertelement <4 x i32> poison, i32 [[DOTSCALAR8]], i64 0
 ; CHECK-NEXT:    [[TMP2:%.*]] = shufflevector <4 x i32> [[TMP1]], <4 x i32> poison, <4 x i32> zeroinitializer
 ; CHECK-NEXT:    [[ADD29:%.*]] = add <4 x i32> [[TMP2]], [[NUM:%.*]]
 ; CHECK-NEXT:    ret <4 x i32> [[ADD29]]
diff --git a/llvm/test/Transforms/SLPVectorizer/X86/alternate-int-inseltpoison.ll b/llvm/test/Transforms/SLPVectorizer/X86/alternate-int-inseltpoison.ll
--- a/llvm/test/Transforms/SLPVectorizer/X86/alternate-int-inseltpoison.ll
+++ b/llvm/test/Transforms/SLPVectorizer/X86/alternate-int-inseltpoison.ll
@@ -425,10 +425,10 @@
 ; CHECK-NEXT:    [[AB5:%.*]] = sdiv i32 [[A5]], 4
 ; CHECK-NEXT:    [[AB6:%.*]] = sdiv i32 [[A6]], 8
 ; CHECK-NEXT:    [[AB7:%.*]] = sdiv i32 [[A7]], 16
-; CHECK-NEXT:    [[TMP1:%.*]] = insertelement <8 x i32> <i32 undef, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison>, i32 [[AB1]], i32 1
-; CHECK-NEXT:    [[TMP2:%.*]] = insertelement <8 x i32> [[TMP1]], i32 [[AB2]], i32 2
-; CHECK-NEXT:    [[R4:%.*]] = insertelement <8 x i32> [[TMP2]], i32 [[AB3]], i32 3
-; CHECK-NEXT:    [[R5:%.*]] = insertelement <8 x i32> [[R4]], i32 [[AB5]], i32 5
+; CHECK-NEXT:    [[R1:%.*]] = insertelement <8 x i32> poison, i32 [[AB1]], i32 1
+; CHECK-NEXT:    [[R2:%.*]] = insertelement <8 x i32> [[R1]], i32 [[AB2]], i32 2
+; CHECK-NEXT:    [[R3:%.*]] = insertelement <8 x i32> [[R2]], i32 [[AB3]], i32 3
+; CHECK-NEXT:    [[R5:%.*]] = insertelement <8 x i32> [[R3]], i32 [[AB5]], i32 5
 ; CHECK-NEXT:    [[R6:%.*]] = insertelement <8 x i32> [[R5]], i32 [[AB6]], i32 6
 ; CHECK-NEXT:    [[R7:%.*]] = insertelement <8 x i32> [[R6]], i32 [[AB7]], i32 7
 ; CHECK-NEXT:    ret <8 x i32> [[R7]]
diff --git a/llvm/test/Transforms/SLPVectorizer/X86/alternate-int.ll b/llvm/test/Transforms/SLPVectorizer/X86/alternate-int.ll
--- a/llvm/test/Transforms/SLPVectorizer/X86/alternate-int.ll
+++ b/llvm/test/Transforms/SLPVectorizer/X86/alternate-int.ll
@@ -425,10 +425,10 @@
 ; CHECK-NEXT:    [[AB5:%.*]] = sdiv i32 [[A5]], 4
 ; CHECK-NEXT:    [[AB6:%.*]] = sdiv i32 [[A6]], 8
 ; CHECK-NEXT:    [[AB7:%.*]] = sdiv i32 [[A7]], 16
-; CHECK-NEXT:    [[TMP1:%.*]] = insertelement <8 x i32> undef, i32 [[AB1]], i32 1
-; CHECK-NEXT:    [[TMP2:%.*]] = insertelement <8 x i32> [[TMP1]], i32 [[AB2]], i32 2
-; CHECK-NEXT:    [[R4:%.*]] = insertelement <8 x i32> [[TMP2]], i32 [[AB3]], i32 3
-; CHECK-NEXT:    [[R5:%.*]] = insertelement <8 x i32> [[R4]], i32 [[AB5]], i32 5
+; CHECK-NEXT:    [[R1:%.*]] = insertelement <8 x i32> <i32 poison, i32 poison, i32 poison, i32 poison, i32 undef, i32 poison, i32 poison, i32 poison>, i32 [[AB1]], i32 1
+; CHECK-NEXT:    [[R2:%.*]] = insertelement <8 x i32> [[R1]], i32 [[AB2]], i32 2
+; CHECK-NEXT:    [[R3:%.*]] = insertelement <8 x i32> [[R2]], i32 [[AB3]], i32 3
+; CHECK-NEXT:    [[R5:%.*]] = insertelement <8 x i32> [[R3]], i32 [[AB5]], i32 5
 ; CHECK-NEXT:    [[R6:%.*]] = insertelement <8 x i32> [[R5]], i32 [[AB6]], i32 6
 ; CHECK-NEXT:    [[R7:%.*]] = insertelement <8 x i32> [[R6]], i32 [[AB7]], i32 7
 ; CHECK-NEXT:    ret <8 x i32> [[R7]]
diff --git a/llvm/test/Transforms/VectorCombine/X86/insert-binop-with-constant.ll b/llvm/test/Transforms/VectorCombine/X86/insert-binop-with-constant.ll
--- a/llvm/test/Transforms/VectorCombine/X86/insert-binop-with-constant.ll
+++ b/llvm/test/Transforms/VectorCombine/X86/insert-binop-with-constant.ll
@@ -131,7 +131,7 @@
 define <2 x i64> @shl_constant_op0(i64 %x) {
 ; CHECK-LABEL: @shl_constant_op0(
 ; CHECK-NEXT:    [[BO_SCALAR:%.*]] = shl i64 2, [[X:%.*]]
-; CHECK-NEXT:    [[BO:%.*]] = insertelement <2 x i64> undef, i64 [[BO_SCALAR]], i64 1
+; CHECK-NEXT:    [[BO:%.*]] = insertelement <2 x i64> poison, i64 [[BO_SCALAR]], i64 1
 ; CHECK-NEXT:    ret <2 x i64> [[BO]]
 ;
   %ins = insertelement <2 x i64> undef, i64 %x, i32 1
@@ -142,7 +142,7 @@
 define <2 x i64> @shl_constant_op0_not_undef_lane(i64 %x) {
 ; CHECK-LABEL: @shl_constant_op0_not_undef_lane(
 ; CHECK-NEXT:    [[BO_SCALAR:%.*]] = shl i64 2, [[X:%.*]]
-; CHECK-NEXT:    [[BO:%.*]] = insertelement <2 x i64> undef, i64 [[BO_SCALAR]], i64 1
+; CHECK-NEXT:    [[BO:%.*]] = insertelement <2 x i64> poison, i64 [[BO_SCALAR]], i64 1
 ; CHECK-NEXT:    ret <2 x i64> [[BO]]
 ;
   %ins = insertelement <2 x i64> undef, i64 %x, i32 1
@@ -224,7 +224,7 @@
 define <2 x i64> @ashr_constant_op0(i64 %x) {
 ; CHECK-LABEL: @ashr_constant_op0(
 ; CHECK-NEXT:    [[BO_SCALAR:%.*]] = ashr exact i64 2, [[X:%.*]]
-; CHECK-NEXT:    [[BO:%.*]] = insertelement <2 x i64> undef, i64 [[BO_SCALAR]], i64 1
+; CHECK-NEXT:    [[BO:%.*]] = insertelement <2 x i64> poison, i64 [[BO_SCALAR]], i64 1
 ; CHECK-NEXT:    ret <2 x i64> [[BO]]
 ;
   %ins = insertelement <2 x i64> undef, i64 %x, i32 1
@@ -235,7 +235,7 @@
 define <2 x i64> @ashr_constant_op0_not_undef_lane(i64 %x) {
 ; CHECK-LABEL: @ashr_constant_op0_not_undef_lane(
 ; CHECK-NEXT:    [[BO_SCALAR:%.*]] = ashr exact i64 2, [[X:%.*]]
-; CHECK-NEXT:    [[BO:%.*]] = insertelement <2 x i64> undef, i64 [[BO_SCALAR]], i64 1
+; CHECK-NEXT:    [[BO:%.*]] = insertelement <2 x i64> poison, i64 [[BO_SCALAR]], i64 1
 ; CHECK-NEXT:    ret <2 x i64> [[BO]]
 ;
   %ins = insertelement <2 x i64> undef, i64 %x, i32 1
@@ -268,7 +268,7 @@
 define <2 x i64> @lshr_constant_op0(i64 %x) {
 ; CHECK-LABEL: @lshr_constant_op0(
 ; CHECK-NEXT:    [[BO_SCALAR:%.*]] = lshr i64 5, [[X:%.*]]
-; CHECK-NEXT:    [[BO:%.*]] = insertelement <2 x i64> undef, i64 [[BO_SCALAR]], i64 0
+; CHECK-NEXT:    [[BO:%.*]] = insertelement <2 x i64> poison, i64 [[BO_SCALAR]], i64 0
 ; CHECK-NEXT:    ret <2 x i64> [[BO]]
 ;
   %ins = insertelement <2 x i64> undef, i64 %x, i32 0
@@ -279,7 +279,7 @@
 define <2 x i64> @lshr_constant_op0_not_undef_lane(i64 %x) {
 ; CHECK-LABEL: @lshr_constant_op0_not_undef_lane(
 ; CHECK-NEXT:    [[BO_SCALAR:%.*]] = lshr i64 5, [[X:%.*]]
-; CHECK-NEXT:    [[BO:%.*]] = insertelement <2 x i64> undef, i64 [[BO_SCALAR]], i64 0
+; CHECK-NEXT:    [[BO:%.*]] = insertelement <2 x i64> poison, i64 [[BO_SCALAR]], i64 0
 ; CHECK-NEXT:    ret <2 x i64> [[BO]]
 ;
   %ins = insertelement <2 x i64> undef, i64 %x, i32 0
@@ -312,7 +312,7 @@
 define <2 x i64> @urem_constant_op0(i64 %x) {
 ; CHECK-LABEL: @urem_constant_op0(
 ; CHECK-NEXT:    [[BO_SCALAR:%.*]] = urem i64 5, [[X:%.*]]
-; CHECK-NEXT:    [[BO:%.*]] = insertelement <2 x i64> undef, i64 [[BO_SCALAR]], i64 0
+; CHECK-NEXT:    [[BO:%.*]] = insertelement <2 x i64> poison, i64 [[BO_SCALAR]], i64 0
 ; CHECK-NEXT:    ret <2 x i64> [[BO]]
 ;
   %ins = insertelement <2 x i64> undef, i64 %x, i32 0
@@ -323,7 +323,7 @@
 define <2 x i64> @urem_constant_op0_not_undef_lane(i64 %x) {
 ; CHECK-LABEL: @urem_constant_op0_not_undef_lane(
 ; CHECK-NEXT:    [[BO_SCALAR:%.*]] = urem i64 5, [[X:%.*]]
-; CHECK-NEXT:    [[BO:%.*]] = insertelement <2 x i64> undef, i64 [[BO_SCALAR]], i64 0
+; CHECK-NEXT:    [[BO:%.*]] = insertelement <2 x i64> poison, i64 [[BO_SCALAR]], i64 0
 ; CHECK-NEXT:    ret <2 x i64> [[BO]]
 ;
   %ins = insertelement <2 x i64> undef, i64 %x, i32 0
@@ -356,7 +356,7 @@
 define <2 x i64> @srem_constant_op0(i64 %x) {
 ; CHECK-LABEL: @srem_constant_op0(
 ; CHECK-NEXT:    [[BO_SCALAR:%.*]] = srem i64 5, [[X:%.*]]
-; CHECK-NEXT:    [[BO:%.*]] = insertelement <2 x i64> undef, i64 [[BO_SCALAR]], i64 0
+; CHECK-NEXT:    [[BO:%.*]] = insertelement <2 x i64> poison, i64 [[BO_SCALAR]], i64 0
 ; CHECK-NEXT:    ret <2 x i64> [[BO]]
 ;
   %ins = insertelement <2 x i64> undef, i64 %x, i32 0
@@ -367,7 +367,7 @@
 define <2 x i64> @srem_constant_op0_not_undef_lane(i64 %x) {
 ; CHECK-LABEL: @srem_constant_op0_not_undef_lane(
 ; CHECK-NEXT:    [[BO_SCALAR:%.*]] = srem i64 5, [[X:%.*]]
-; CHECK-NEXT:    [[BO:%.*]] = insertelement <2 x i64> undef, i64 [[BO_SCALAR]], i64 0
+; CHECK-NEXT:    [[BO:%.*]] = insertelement <2 x i64> poison, i64 [[BO_SCALAR]], i64 0
 ; CHECK-NEXT:    ret <2 x i64> [[BO]]
 ;
   %ins = insertelement <2 x i64> undef, i64 %x, i32 0
@@ -400,7 +400,7 @@
 define <2 x i64> @udiv_constant_op0(i64 %x) {
 ; CHECK-LABEL: @udiv_constant_op0(
 ; CHECK-NEXT:    [[BO_SCALAR:%.*]] = udiv exact i64 5, [[X:%.*]]
-; CHECK-NEXT:    [[BO:%.*]] = insertelement <2 x i64> undef, i64 [[BO_SCALAR]], i64 0
+; CHECK-NEXT:    [[BO:%.*]] = insertelement <2 x i64> poison, i64 [[BO_SCALAR]], i64 0
 ; CHECK-NEXT:    ret <2 x i64> [[BO]]
 ;
   %ins = insertelement <2 x i64> undef, i64 %x, i32 0
@@ -411,7 +411,7 @@
 define <2 x i64> @udiv_constant_op0_not_undef_lane(i64 %x) {
 ; CHECK-LABEL: @udiv_constant_op0_not_undef_lane(
 ; CHECK-NEXT:    [[BO_SCALAR:%.*]] = udiv exact i64 5, [[X:%.*]]
-; CHECK-NEXT:    [[BO:%.*]] = insertelement <2 x i64> undef, i64 [[BO_SCALAR]], i64 0
+; CHECK-NEXT:    [[BO:%.*]] = insertelement <2 x i64> poison, i64 [[BO_SCALAR]], i64 0
 ; CHECK-NEXT:    ret <2 x i64> [[BO]]
 ;
   %ins = insertelement <2 x i64> undef, i64 %x, i32 0
@@ -444,7 +444,7 @@
 define <2 x i64> @sdiv_constant_op0(i64 %x) {
 ; CHECK-LABEL: @sdiv_constant_op0(
 ; CHECK-NEXT:    [[BO_SCALAR:%.*]] = sdiv i64 5, [[X:%.*]]
-; CHECK-NEXT:    [[BO:%.*]] = insertelement <2 x i64> undef, i64 [[BO_SCALAR]], i64 0
+; CHECK-NEXT:    [[BO:%.*]] = insertelement <2 x i64> poison, i64 [[BO_SCALAR]], i64 0
 ; CHECK-NEXT:    ret <2 x i64> [[BO]]
 ;
   %ins = insertelement <2 x i64> undef, i64 %x, i32 0
@@ -455,7 +455,7 @@
 define <2 x i64> @sdiv_constant_op0_not_undef_lane(i64 %x) {
 ; CHECK-LABEL: @sdiv_constant_op0_not_undef_lane(
 ; CHECK-NEXT:    [[BO_SCALAR:%.*]] = sdiv i64 5, [[X:%.*]]
-; CHECK-NEXT:    [[BO:%.*]] = insertelement <2 x i64> undef, i64 [[BO_SCALAR]], i64 0
+; CHECK-NEXT:    [[BO:%.*]] = insertelement <2 x i64> poison, i64 [[BO_SCALAR]], i64 0
 ; CHECK-NEXT:    ret <2 x i64> [[BO]]
 ;
   %ins = insertelement <2 x i64> undef, i64 %x, i32 0
diff --git a/llvm/test/Transforms/VectorCombine/X86/insert-binop.ll b/llvm/test/Transforms/VectorCombine/X86/insert-binop.ll
--- a/llvm/test/Transforms/VectorCombine/X86/insert-binop.ll
+++ b/llvm/test/Transforms/VectorCombine/X86/insert-binop.ll
@@ -53,7 +53,7 @@
 ; CHECK-NEXT:    [[S0_SCALAR:%.*]] = sub i64 [[W:%.*]], [[X:%.*]]
 ; CHECK-NEXT:    [[S1_SCALAR:%.*]] = or i64 [[S0_SCALAR]], [[Y:%.*]]
 ; CHECK-NEXT:    [[S2_SCALAR:%.*]] = shl i64 [[Z:%.*]], [[S1_SCALAR]]
-; CHECK-NEXT:    [[S2:%.*]] = insertelement <2 x i64> undef, i64 [[S2_SCALAR]], i64 1
+; CHECK-NEXT:    [[S2:%.*]] = insertelement <2 x i64> poison, i64 [[S2_SCALAR]], i64 1
 ; CHECK-NEXT:    ret <2 x i64> [[S2]]
 ;
   %i0 = insertelement <2 x i64> undef, i64 %w, i64 1
diff --git a/llvm/unittests/IR/ConstantsTest.cpp b/llvm/unittests/IR/ConstantsTest.cpp
--- a/llvm/unittests/IR/ConstantsTest.cpp
+++ b/llvm/unittests/IR/ConstantsTest.cpp
@@ -631,9 +631,17 @@
 
   Type *Int32Ty = Type::getInt32Ty(Context);
   Constant *CU = UndefValue::get(Int32Ty);
+  Constant *CP = PoisonValue::get(Int32Ty);
   Constant *C1 = ConstantInt::get(Int32Ty, 1);
   Constant *C2 = ConstantInt::get(Int32Ty, 2);
 
+  Constant *CUU = ConstantVector::get({CU, CU});
+  Constant *CPP = ConstantVector::get({CP, CP});
+  Constant *CUP = ConstantVector::get({CU, CP});
+  EXPECT_EQ(CUU, UndefValue::get(CUU->getType()));
+  EXPECT_EQ(CPP, PoisonValue::get(CPP->getType()));
+  EXPECT_NE(CUP, UndefValue::get(CUP->getType()));
+
   Constant *C1211 = ConstantVector::get({C1, C2, C1, C1});
   Constant *C12U1 = ConstantVector::get({C1, C2, CU, C1});
   Constant *C12U2 = ConstantVector::get({C1, C2, CU, C2});