diff --git a/llvm/lib/Target/AArch64/AArch64TargetTransformInfo.cpp b/llvm/lib/Target/AArch64/AArch64TargetTransformInfo.cpp
--- a/llvm/lib/Target/AArch64/AArch64TargetTransformInfo.cpp
+++ b/llvm/lib/Target/AArch64/AArch64TargetTransformInfo.cpp
@@ -2633,7 +2633,7 @@
       if (Inst->getArgOperand(i)->getType() != ST->getElementType(i))
         return nullptr;
     }
-    Value *Res = UndefValue::get(ExpectedType);
+    Value *Res = PoisonValue::get(ExpectedType);
     IRBuilder<> Builder(Inst);
     for (unsigned i = 0, e = NumElts; i != e; ++i) {
       Value *L = Inst->getArgOperand(i);
diff --git a/llvm/lib/Target/X86/X86InstCombineIntrinsic.cpp b/llvm/lib/Target/X86/X86InstCombineIntrinsic.cpp
--- a/llvm/lib/Target/X86/X86InstCombineIntrinsic.cpp
+++ b/llvm/lib/Target/X86/X86InstCombineIntrinsic.cpp
@@ -548,7 +548,7 @@
     Value *UAddResult = Builder.CreateExtractValue(UAdd, 0);
     Value *UAddOV = Builder.CreateZExt(Builder.CreateExtractValue(UAdd, 1),
                                        Builder.getInt8Ty());
-    Value *Res = UndefValue::get(RetTy);
+    Value *Res = PoisonValue::get(RetTy);
     Res = Builder.CreateInsertValue(Res, UAddOV, 0);
     return Builder.CreateInsertValue(Res, UAddResult, 1);
   }
diff --git a/llvm/lib/Transforms/Instrumentation/DataFlowSanitizer.cpp b/llvm/lib/Transforms/Instrumentation/DataFlowSanitizer.cpp
--- a/llvm/lib/Transforms/Instrumentation/DataFlowSanitizer.cpp
+++ b/llvm/lib/Transforms/Instrumentation/DataFlowSanitizer.cpp
@@ -2465,7 +2465,7 @@
   if (LeftSize >= ShadowVecSize) {
     auto *ShadowVecTy =
         FixedVectorType::get(DFS.PrimitiveShadowTy, ShadowVecSize);
-    Value *ShadowVec = UndefValue::get(ShadowVecTy);
+    Value *ShadowVec = PoisonValue::get(ShadowVecTy);
     for (unsigned I = 0; I != ShadowVecSize; ++I) {
       ShadowVec = IRB.CreateInsertElement(
           ShadowVec, PrimitiveShadow,
diff --git a/llvm/lib/Transforms/Scalar/ScalarizeMaskedMemIntrin.cpp b/llvm/lib/Transforms/Scalar/ScalarizeMaskedMemIntrin.cpp
--- a/llvm/lib/Transforms/Scalar/ScalarizeMaskedMemIntrin.cpp
+++ b/llvm/lib/Transforms/Scalar/ScalarizeMaskedMemIntrin.cpp
@@ -656,7 +656,7 @@
   // shuffle blend with the pass through value.
   if (isConstantIntVector(Mask)) {
     unsigned MemIndex = 0;
-    VResult = UndefValue::get(VecType);
+    VResult = PoisonValue::get(VecType);
     SmallVector<int, 16> ShuffleMask(VectorWidth, UndefMaskElem);
     for (unsigned Idx = 0; Idx < VectorWidth; ++Idx) {
       Value *InsertElt;
diff --git a/llvm/lib/Transforms/Scalar/Scalarizer.cpp b/llvm/lib/Transforms/Scalar/Scalarizer.cpp
--- a/llvm/lib/Transforms/Scalar/Scalarizer.cpp
+++ b/llvm/lib/Transforms/Scalar/Scalarizer.cpp
@@ -848,7 +848,7 @@
   if (!ScalarizeVariableInsertExtract)
     return false;
 
-  Value *Res = UndefValue::get(VT->getElementType());
+  Value *Res = PoisonValue::get(VT->getElementType());
   for (unsigned I = 0; I < NumSrcElems; ++I) {
     Value *ShouldExtract =
         Builder.CreateICmpEQ(ExtIdx, ConstantInt::get(ExtIdx->getType(), I),
diff --git a/llvm/test/Instrumentation/DataFlowSanitizer/array.ll b/llvm/test/Instrumentation/DataFlowSanitizer/array.ll
--- a/llvm/test/Instrumentation/DataFlowSanitizer/array.ll
+++ b/llvm/test/Instrumentation/DataFlowSanitizer/array.ll
@@ -257,7 +257,7 @@
   ; FAST: %[[#R+31]] = or i[[#SBITS]] %[[#R+29]], %[[#R+30]]
   ; FAST: %[[#R+32]] = extractvalue [17 x i[[#SBITS]]] %[[#R]], 16
   ; FAST: %[[#R+33]] = or i[[#SBITS]] %[[#R+31]], %[[#R+32]]
-  ; FAST: %[[#VREG:]]  = insertelement <8 x i[[#SBITS]]> undef, i[[#SBITS]] %[[#R+33]], i32 0
+  ; FAST: %[[#VREG:]]  = insertelement <8 x i[[#SBITS]]> poison, i[[#SBITS]] %[[#R+33]], i32 0
   ; FAST: %[[#VREG+1]] = insertelement <8 x i[[#SBITS]]> %[[#VREG]], i[[#SBITS]] %[[#R+33]], i32 1
   ; FAST: %[[#VREG+2]] = insertelement <8 x i[[#SBITS]]> %[[#VREG+1]], i[[#SBITS]] %[[#R+33]], i32 2
   ; FAST: %[[#VREG+3]] = insertelement <8 x i[[#SBITS]]> %[[#VREG+2]], i[[#SBITS]] %[[#R+33]], i32 3
diff --git a/llvm/test/Transforms/ScalarizeMaskedMemIntrin/X86/expand-masked-expandload.ll b/llvm/test/Transforms/ScalarizeMaskedMemIntrin/X86/expand-masked-expandload.ll
--- a/llvm/test/Transforms/ScalarizeMaskedMemIntrin/X86/expand-masked-expandload.ll
+++ b/llvm/test/Transforms/ScalarizeMaskedMemIntrin/X86/expand-masked-expandload.ll
@@ -34,7 +34,7 @@
 ; CHECK-LABEL: @scalarize_v2i64_ones_mask(
 ; CHECK-NEXT:    [[TMP1:%.*]] = getelementptr inbounds i64, i64* [[P:%.*]], i32 0
 ; CHECK-NEXT:    [[LOAD0:%.*]] = load i64, i64* [[TMP1]], align 1
-; CHECK-NEXT:    [[RES0:%.*]] = insertelement <2 x i64> undef, i64 [[LOAD0]], i64 0
+; CHECK-NEXT:    [[RES0:%.*]] = insertelement <2 x i64> poison, i64 [[LOAD0]], i64 0
 ; CHECK-NEXT:    [[TMP2:%.*]] = getelementptr inbounds i64, i64* [[P]], i32 1
 ; CHECK-NEXT:    [[LOAD1:%.*]] = load i64, i64* [[TMP2]], align 1
 ; CHECK-NEXT:    [[RES1:%.*]] = insertelement <2 x i64> [[RES0]], i64 [[LOAD1]], i64 1
@@ -58,7 +58,7 @@
 ; CHECK-LABEL: @scalarize_v2i64_const_mask(
 ; CHECK-NEXT:    [[TMP1:%.*]] = getelementptr inbounds i64, i64* [[P:%.*]], i32 0
 ; CHECK-NEXT:    [[LOAD1:%.*]] = load i64, i64* [[TMP1]], align 1
-; CHECK-NEXT:    [[RES1:%.*]] = insertelement <2 x i64> undef, i64 [[LOAD1]], i64 1
+; CHECK-NEXT:    [[RES1:%.*]] = insertelement <2 x i64> <i64 undef, i64 poison>, i64 [[LOAD1]], i64 1
 ; CHECK-NEXT:    [[TMP2:%.*]] = shufflevector <2 x i64> [[RES1]], <2 x i64> [[PASSTHRU:%.*]], <2 x i32> <i32 2, i32 1>
 ; CHECK-NEXT:    ret <2 x i64> [[TMP2]]
 ;
diff --git a/llvm/test/Transforms/Scalarizer/variable-extractelement.ll b/llvm/test/Transforms/Scalarizer/variable-extractelement.ll
--- a/llvm/test/Transforms/Scalarizer/variable-extractelement.ll
+++ b/llvm/test/Transforms/Scalarizer/variable-extractelement.ll
@@ -10,7 +10,7 @@
 ; DEFAULT-LABEL: @f1(
 ; DEFAULT-NEXT:    [[INDEX_IS_0:%.*]] = icmp eq i32 [[INDEX:%.*]], 0
 ; DEFAULT-NEXT:    [[SRC_I0:%.*]] = extractelement <4 x i32> [[SRC:%.*]], i32 0
-; DEFAULT-NEXT:    [[RES_UPTO0:%.*]] = select i1 [[INDEX_IS_0]], i32 [[SRC_I0]], i32 undef
+; DEFAULT-NEXT:    [[RES_UPTO0:%.*]] = select i1 [[INDEX_IS_0]], i32 [[SRC_I0]], i32 poison
 ; DEFAULT-NEXT:    [[INDEX_IS_1:%.*]] = icmp eq i32 [[INDEX]], 1
 ; DEFAULT-NEXT:    [[SRC_I1:%.*]] = extractelement <4 x i32> [[SRC]], i32 1
 ; DEFAULT-NEXT:    [[RES_UPTO1:%.*]] = select i1 [[INDEX_IS_1]], i32 [[SRC_I1]], i32 [[RES_UPTO0]]
@@ -42,7 +42,7 @@
 ; DEFAULT-NEXT:    [[VAL0_I3:%.*]] = extractelement <4 x i32> [[VAL0]], i32 3
 ; DEFAULT-NEXT:    [[VAL1_I3:%.*]] = shl i32 4, [[VAL0_I3]]
 ; DEFAULT-NEXT:    [[INDEX_IS_0:%.*]] = icmp eq i32 [[INDEX:%.*]], 0
-; DEFAULT-NEXT:    [[VAL2_UPTO0:%.*]] = select i1 [[INDEX_IS_0]], i32 [[VAL1_I0]], i32 undef
+; DEFAULT-NEXT:    [[VAL2_UPTO0:%.*]] = select i1 [[INDEX_IS_0]], i32 [[VAL1_I0]], i32 poison
 ; DEFAULT-NEXT:    [[INDEX_IS_1:%.*]] = icmp eq i32 [[INDEX]], 1
 ; DEFAULT-NEXT:    [[VAL2_UPTO1:%.*]] = select i1 [[INDEX_IS_1]], i32 [[VAL1_I1]], i32 [[VAL2_UPTO0]]
 ; DEFAULT-NEXT:    [[INDEX_IS_2:%.*]] = icmp eq i32 [[INDEX]], 2
diff --git a/llvm/test/Transforms/Scalarizer/vector-of-pointer-to-vector.ll b/llvm/test/Transforms/Scalarizer/vector-of-pointer-to-vector.ll
--- a/llvm/test/Transforms/Scalarizer/vector-of-pointer-to-vector.ll
+++ b/llvm/test/Transforms/Scalarizer/vector-of-pointer-to-vector.ll
@@ -6,7 +6,7 @@
 ; CHECK-LABEL: @f1(
 ; CHECK-NEXT:    [[INDEX_IS_0:%.*]] = icmp eq i32 [[INDEX:%.*]], 0
 ; CHECK-NEXT:    [[SRC_I0:%.*]] = extractelement <1 x ptr> [[SRC:%.*]], i32 0
-; CHECK-NEXT:    [[DOTUPTO0:%.*]] = select i1 [[INDEX_IS_0]], ptr [[SRC_I0]], ptr undef
+; CHECK-NEXT:    [[DOTUPTO0:%.*]] = select i1 [[INDEX_IS_0]], ptr [[SRC_I0]], ptr poison
 ; CHECK-NEXT:    [[DOTI0:%.*]] = load i32, ptr [[DOTUPTO0]], align 4
 ; CHECK-NEXT:    [[TMP1:%.*]] = insertelement <1 x i32> poison, i32 [[DOTI0]], i32 0
 ; CHECK-NEXT:    ret <1 x i32> [[TMP1]]
@@ -32,7 +32,7 @@
 ; CHECK-LABEL: @f2(
 ; CHECK-NEXT:    [[INDEX_IS_0:%.*]] = icmp eq i32 [[INDEX:%.*]], 0
 ; CHECK-NEXT:    [[SRC_I0:%.*]] = extractelement <1 x ptr> [[SRC:%.*]], i32 0
-; CHECK-NEXT:    [[DOTUPTO0:%.*]] = select i1 [[INDEX_IS_0]], ptr [[SRC_I0]], ptr undef
+; CHECK-NEXT:    [[DOTUPTO0:%.*]] = select i1 [[INDEX_IS_0]], ptr [[SRC_I0]], ptr poison
 ; CHECK-NEXT:    [[DOTUPTO0_I1:%.*]] = getelementptr i32, ptr [[DOTUPTO0]], i32 1
 ; CHECK-NEXT:    [[DOTI0:%.*]] = load i32, ptr [[DOTUPTO0]], align 4
 ; CHECK-NEXT:    [[DOTI1:%.*]] = load i32, ptr [[DOTUPTO0_I1]], align 4
@@ -66,7 +66,7 @@
 ; CHECK-NEXT:    [[VAL_I1:%.*]] = extractelement <2 x i32> [[VAL]], i32 1
 ; CHECK-NEXT:    [[INDEX_IS_0:%.*]] = icmp eq i32 [[INDEX:%.*]], 0
 ; CHECK-NEXT:    [[SRC_I0:%.*]] = extractelement <1 x ptr> [[SRC:%.*]], i32 0
-; CHECK-NEXT:    [[DOTUPTO0:%.*]] = select i1 [[INDEX_IS_0]], ptr [[SRC_I0]], ptr undef
+; CHECK-NEXT:    [[DOTUPTO0:%.*]] = select i1 [[INDEX_IS_0]], ptr [[SRC_I0]], ptr poison
 ; CHECK-NEXT:    [[DOTUPTO0_I1:%.*]] = getelementptr i32, ptr [[DOTUPTO0]], i32 1
 ; CHECK-NEXT:    store i32 [[VAL_I0]], ptr [[DOTUPTO0]], align 4
 ; CHECK-NEXT:    store i32 [[VAL_I1]], ptr [[DOTUPTO0_I1]], align 4