diff --git a/clang/test/CodeGen/SystemZ/builtins-systemz-zvector-constrained.c b/clang/test/CodeGen/SystemZ/builtins-systemz-zvector-constrained.c
--- a/clang/test/CodeGen/SystemZ/builtins-systemz-zvector-constrained.c
+++ b/clang/test/CodeGen/SystemZ/builtins-systemz-zvector-constrained.c
@@ -37,7 +37,7 @@
   // CHECK-ASM: vlvgg
 
   vd = vec_promote(d, idx);
-  // CHECK: insertelement <2 x double> undef, double %{{.*}}, i32 %{{.*}}
+  // CHECK: insertelement <2 x double> poison, double %{{.*}}, i32 %{{.*}}
   // CHECK-ASM: vlvgg
 
   vd = vec_insert_and_zero(cptrd);
diff --git a/clang/test/CodeGen/SystemZ/builtins-systemz-zvector.c b/clang/test/CodeGen/SystemZ/builtins-systemz-zvector.c
--- a/clang/test/CodeGen/SystemZ/builtins-systemz-zvector.c
+++ b/clang/test/CodeGen/SystemZ/builtins-systemz-zvector.c
@@ -166,31 +166,31 @@
   // CHECK-ASM: vlvgg
 
   vsc = vec_promote(sc, idx);
-  // CHECK: insertelement <16 x i8> undef, i8 %{{.*}}, i32 %{{.*}}
+  // CHECK: insertelement <16 x i8> poison, i8 %{{.*}}, i32 %{{.*}}
   // CHECK-ASM: vlvgb
   vuc = vec_promote(uc, idx);
-  // CHECK: insertelement <16 x i8> undef, i8 %{{.*}}, i32 %{{.*}}
+  // CHECK: insertelement <16 x i8> poison, i8 %{{.*}}, i32 %{{.*}}
   // CHECK-ASM: vlvgb
   vss = vec_promote(ss, idx);
-  // CHECK: insertelement <8 x i16> undef, i16 %{{.*}}, i32 %{{.*}}
+  // CHECK: insertelement <8 x i16> poison, i16 %{{.*}}, i32 %{{.*}}
   // CHECK-ASM: vlvgh
   vus = vec_promote(us, idx);
-  // CHECK: insertelement <8 x i16> undef, i16 %{{.*}}, i32 %{{.*}}
+  // CHECK: insertelement <8 x i16> poison, i16 %{{.*}}, i32 %{{.*}}
   // CHECK-ASM: vlvgh
   vsi = vec_promote(si, idx);
-  // CHECK: insertelement <4 x i32> undef, i32 %{{.*}}, i32 %{{.*}}
+  // CHECK: insertelement <4 x i32> poison, i32 %{{.*}}, i32 %{{.*}}
   // CHECK-ASM: vlvgf
   vui = vec_promote(ui, idx);
-  // CHECK: insertelement <4 x i32> undef, i32 %{{.*}}, i32 %{{.*}}
+  // CHECK: insertelement <4 x i32> poison, i32 %{{.*}}, i32 %{{.*}}
   // CHECK-ASM: vlvgf
   vsl = vec_promote(sl, idx);
-  // CHECK: insertelement <2 x i64> undef, i64 %{{.*}}, i32 %{{.*}}
+  // CHECK: insertelement <2 x i64> poison, i64 %{{.*}}, i32 %{{.*}}
   // CHECK-ASM: vlvgg
   vul = vec_promote(ul, idx);
-  // CHECK: insertelement <2 x i64> undef, i64 %{{.*}}, i32 %{{.*}}
+  // CHECK: insertelement <2 x i64> poison, i64 %{{.*}}, i32 %{{.*}}
   // CHECK-ASM: vlvgg
   vd = vec_promote(d, idx);
-  // CHECK: insertelement <2 x double> undef, double %{{.*}}, i32 %{{.*}}
+  // CHECK: insertelement <2 x double> poison, double %{{.*}}, i32 %{{.*}}
   // CHECK-ASM: vlvgg
 
   vsc = vec_insert_and_zero(cptrsc);
diff --git a/clang/test/CodeGen/SystemZ/builtins-systemz-zvector2-constrained.c b/clang/test/CodeGen/SystemZ/builtins-systemz-zvector2-constrained.c
--- a/clang/test/CodeGen/SystemZ/builtins-systemz-zvector2-constrained.c
+++ b/clang/test/CodeGen/SystemZ/builtins-systemz-zvector2-constrained.c
@@ -70,10 +70,10 @@
   // CHECK-ASM: vlvgg
 
   vf = vec_promote(f, idx);
-  // CHECK: insertelement <4 x float> undef, float %{{.*}}, i32 %{{.*}}
+  // CHECK: insertelement <4 x float> poison, float %{{.*}}, i32 %{{.*}}
   // CHECK-ASM: vlvgf
   vd = vec_promote(d, idx);
-  // CHECK: insertelement <2 x double> undef, double %{{.*}}, i32 %{{.*}}
+  // CHECK: insertelement <2 x double> poison, double %{{.*}}, i32 %{{.*}}
   // CHECK-ASM: vlvgg
 
   vf = vec_insert_and_zero(cptrf);
diff --git a/clang/test/CodeGen/SystemZ/builtins-systemz-zvector2.c b/clang/test/CodeGen/SystemZ/builtins-systemz-zvector2.c
--- a/clang/test/CodeGen/SystemZ/builtins-systemz-zvector2.c
+++ b/clang/test/CodeGen/SystemZ/builtins-systemz-zvector2.c
@@ -102,10 +102,10 @@
   // CHECK-ASM: vlvgg
 
   vf = vec_promote(f, idx);
-  // CHECK: insertelement <4 x float> undef, float %{{.*}}, i32 %{{.*}}
+  // CHECK: insertelement <4 x float> poison, float %{{.*}}, i32 %{{.*}}
   // CHECK-ASM: vlvgf
   vd = vec_promote(d, idx);
-  // CHECK: insertelement <2 x double> undef, double %{{.*}}, i32 %{{.*}}
+  // CHECK: insertelement <2 x double> poison, double %{{.*}}, i32 %{{.*}}
   // CHECK-ASM: vlvgg
 
   vf = vec_insert_and_zero(cptrf);
diff --git a/llvm/lib/IR/ConstantFold.cpp b/llvm/lib/IR/ConstantFold.cpp
--- a/llvm/lib/IR/ConstantFold.cpp
+++ b/llvm/lib/IR/ConstantFold.cpp
@@ -710,9 +710,9 @@
       ElementCount::get(MaskNumElts, isa<ScalableVectorType>(V1VTy));
   Type *EltTy = V1VTy->getElementType();
 
-  // Undefined shuffle mask -> undefined value.
+  // Poison shuffle mask -> poison value.
   if (all_of(Mask, [](int Elt) { return Elt == PoisonMaskElem; })) {
-    return UndefValue::get(VectorType::get(EltTy, MaskEltCount));
+    return PoisonValue::get(VectorType::get(EltTy, MaskEltCount));
   }
 
   // If the mask is all zeros this is a splat, no need to go through all
diff --git a/llvm/lib/IR/Instructions.cpp b/llvm/lib/IR/Instructions.cpp
--- a/llvm/lib/IR/Instructions.cpp
+++ b/llvm/lib/IR/Instructions.cpp
@@ -2290,7 +2290,7 @@
   SmallVector<Constant *, 16> MaskConst;
   for (int Elem : Mask) {
     if (Elem == PoisonMaskElem)
-      MaskConst.push_back(UndefValue::get(Int32Ty));
+      MaskConst.push_back(PoisonValue::get(Int32Ty));
     else
       MaskConst.push_back(ConstantInt::get(Int32Ty, Elem));
   }
diff --git a/llvm/test/Transforms/InstCombine/shufflevec-constant.ll b/llvm/test/Transforms/InstCombine/shufflevec-constant.ll
--- a/llvm/test/Transforms/InstCombine/shufflevec-constant.ll
+++ b/llvm/test/Transforms/InstCombine/shufflevec-constant.ll
@@ -18,7 +18,7 @@
 
 define <4 x i1> @shuffle_undef_fixed() {
 ; CHECK-LABEL: @shuffle_undef_fixed(
-; CHECK-NEXT:    ret <4 x i1> undef
+; CHECK-NEXT:    ret <4 x i1> poison
 ;
   %S = shufflevector <4 x i1> zeroinitializer, <4 x i1> zeroinitializer, <4 x i32> undef
   ret <4 x i1> %S
@@ -26,7 +26,7 @@
 
 define <vscale x 4 x i1> @suffle_undef_scalable() {
 ; CHECK-LABEL: @suffle_undef_scalable(
-; CHECK-NEXT:    ret <vscale x 4 x i1> undef
+; CHECK-NEXT:    ret <vscale x 4 x i1> poison
 ;
   %S = shufflevector <vscale x 4 x i1> zeroinitializer, <vscale x 4 x i1> zeroinitializer, <vscale x 4 x i32> undef
   ret <vscale x 4 x i1> %S