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
@@ -924,19 +924,19 @@
                              const SimplifyQuery &Q) {
   Type *Ty = Op0->getType();
 
-  // X / undef -> undef
-  // X % undef -> undef
+  // X / undef -> poison
+  // X % undef -> poison
   if (Q.isUndefValue(Op1))
-    return Op1;
+    return PoisonValue::get(Ty);
 
-  // X / 0 -> undef
-  // X % 0 -> undef
+  // X / 0 -> poison
+  // X % 0 -> poison
   // We don't need to preserve faults!
   if (match(Op1, m_Zero()))
-    return UndefValue::get(Ty);
+    return PoisonValue::get(Ty);
 
-  // If any element of a constant divisor fixed width vector is zero or undef,
-  // the whole op is undef.
+  // If any element of a constant divisor fixed width vector is zero or undef
+  // the behavior is undefined and we can fold the whole op to poison.
   auto *Op1C = dyn_cast<Constant>(Op1);
   auto *VTy = dyn_cast<FixedVectorType>(Ty);
   if (Op1C && VTy) {
@@ -944,7 +944,7 @@
     for (unsigned i = 0; i != NumElts; ++i) {
       Constant *Elt = Op1C->getAggregateElement(i);
       if (Elt && (Elt->isNullValue() || Q.isUndefValue(Elt)))
-        return UndefValue::get(Ty);
+        return PoisonValue::get(Ty);
     }
   }
 
diff --git a/llvm/test/Transforms/InstCombine/add-shl-sdiv-to-srem.ll b/llvm/test/Transforms/InstCombine/add-shl-sdiv-to-srem.ll
--- a/llvm/test/Transforms/InstCombine/add-shl-sdiv-to-srem.ll
+++ b/llvm/test/Transforms/InstCombine/add-shl-sdiv-to-srem.ll
@@ -212,7 +212,7 @@
 
 define <3 x i8> @add-shl-sdiv-3xi8-undef0(<3 x i8> %x) {
 ; CHECK-LABEL: @add-shl-sdiv-3xi8-undef0(
-; CHECK-NEXT:    ret <3 x i8> [[X:%.*]]
+; CHECK-NEXT:    ret <3 x i8> poison
 ;
   %sd = sdiv <3 x i8> %x, <i8 -4, i8 undef, i8 -4>
   %sl = shl <3 x i8> %sd, <i8 2, i8 2, i8 2>
diff --git a/llvm/test/Transforms/InstCombine/div.ll b/llvm/test/Transforms/InstCombine/div.ll
--- a/llvm/test/Transforms/InstCombine/div.ll
+++ b/llvm/test/Transforms/InstCombine/div.ll
@@ -40,7 +40,7 @@
 
 define <2 x i64> @sdiv_by_minus1_vec_undef_elt(<2 x i64> %x) {
 ; CHECK-LABEL: @sdiv_by_minus1_vec_undef_elt(
-; CHECK-NEXT:    ret <2 x i64> undef
+; CHECK-NEXT:    ret <2 x i64> poison
 ;
   %div = sdiv <2 x i64> %x, <i64 -1, i64 undef>
   ret <2 x i64> %div
@@ -514,7 +514,7 @@
 
 define <2 x i8> @sdiv_negated_dividend_constant_divisor_vec_undef(<2 x i8> %x) {
 ; CHECK-LABEL: @sdiv_negated_dividend_constant_divisor_vec_undef(
-; CHECK-NEXT:    ret <2 x i8> undef
+; CHECK-NEXT:    ret <2 x i8> poison
 ;
   %neg = sub nsw <2 x i8> zeroinitializer, %x
   %d = sdiv <2 x i8> %neg, <i8 -128, i8 undef>
@@ -523,8 +523,8 @@
 
 define <2 x i64> @sdiv_negated_dividend_constant_divisor_vec(<2 x i64> %x) {
 ; CHECK-LABEL: @sdiv_negated_dividend_constant_divisor_vec(
-; CHECK-NEXT:    [[DIV:%.*]] = sdiv <2 x i64> [[X:%.*]], <i64 -3, i64 -4>
-; CHECK-NEXT:    ret <2 x i64> [[DIV]]
+; CHECK-NEXT:    [[DIV1_NEG:%.*]] = sdiv <2 x i64> [[X:%.*]], <i64 -3, i64 -4>
+; CHECK-NEXT:    ret <2 x i64> [[DIV1_NEG]]
 ;
   %neg = sub nsw <2 x i64> zeroinitializer, %x
   %div = sdiv <2 x i64> %neg, <i64 3, i64 4>
@@ -533,8 +533,8 @@
 
 define <2 x i64> @sdiv_exact_negated_dividend_constant_divisor_vec(<2 x i64> %x) {
 ; CHECK-LABEL: @sdiv_exact_negated_dividend_constant_divisor_vec(
-; CHECK-NEXT:    [[DIV:%.*]] = sdiv exact <2 x i64> [[X:%.*]], <i64 -3, i64 -4>
-; CHECK-NEXT:    ret <2 x i64> [[DIV]]
+; CHECK-NEXT:    [[DIV1_NEG:%.*]] = sdiv exact <2 x i64> [[X:%.*]], <i64 -3, i64 -4>
+; CHECK-NEXT:    ret <2 x i64> [[DIV1_NEG]]
 ;
   %neg = sub nsw <2 x i64> zeroinitializer, %x
   %div = sdiv exact <2 x i64> %neg, <i64 3, i64 4>
@@ -849,8 +849,8 @@
 
 define i32 @test_exact_nsw_exact(i32 %x) {
 ; CHECK-LABEL: @test_exact_nsw_exact(
-; CHECK-NEXT:    [[NEG:%.*]] = sdiv exact i32 [[X:%.*]], -3
-; CHECK-NEXT:    ret i32 [[NEG]]
+; CHECK-NEXT:    [[DIV_NEG:%.*]] = sdiv exact i32 [[X:%.*]], -3
+; CHECK-NEXT:    ret i32 [[DIV_NEG]]
 ;
   %div = sdiv exact i32 %x, 3
   %neg = sub nsw i32 0, %div
@@ -859,8 +859,8 @@
 
 define <2 x i64> @test_exact_vec(<2 x i64> %x) {
 ; CHECK-LABEL: @test_exact_vec(
-; CHECK-NEXT:    [[NEG:%.*]] = sdiv exact <2 x i64> [[X:%.*]], <i64 -3, i64 -4>
-; CHECK-NEXT:    ret <2 x i64> [[NEG]]
+; CHECK-NEXT:    [[DIV_NEG:%.*]] = sdiv exact <2 x i64> [[X:%.*]], <i64 -3, i64 -4>
+; CHECK-NEXT:    ret <2 x i64> [[DIV_NEG]]
 ;
   %div = sdiv exact <2 x i64> %x, <i64 3, i64 4>
   %neg = sub nsw <2 x i64> zeroinitializer, %div
@@ -871,8 +871,8 @@
 
 define <2 x i8> @negate_sdiv_vec_splat(<2 x i8> %x) {
 ; CHECK-LABEL: @negate_sdiv_vec_splat(
-; CHECK-NEXT:    [[NEG:%.*]] = sdiv <2 x i8> [[X:%.*]], <i8 -42, i8 -42>
-; CHECK-NEXT:    ret <2 x i8> [[NEG]]
+; CHECK-NEXT:    [[DIV_NEG:%.*]] = sdiv <2 x i8> [[X:%.*]], <i8 -42, i8 -42>
+; CHECK-NEXT:    ret <2 x i8> [[DIV_NEG]]
 ;
   %div = sdiv <2 x i8> %x, <i8 42, i8 42>
   %neg = sub <2 x i8> zeroinitializer, %div
@@ -883,7 +883,7 @@
 
 define <2 x i8> @negate_sdiv_vec_undef_elt(<2 x i8> %x) {
 ; CHECK-LABEL: @negate_sdiv_vec_undef_elt(
-; CHECK-NEXT:    ret <2 x i8> undef
+; CHECK-NEXT:    ret <2 x i8> poison
 ;
   %div = sdiv <2 x i8> %x, <i8 undef, i8 42>
   %neg = sub <2 x i8> zeroinitializer, %div
@@ -907,8 +907,8 @@
 define <2 x i8> @negate_sdiv_vec_splat_signed_min(<2 x i8> %x) {
 ; CHECK-LABEL: @negate_sdiv_vec_splat_signed_min(
 ; CHECK-NEXT:    [[TMP1:%.*]] = icmp eq <2 x i8> [[X:%.*]], <i8 -128, i8 -128>
-; CHECK-NEXT:    [[NEG:%.*]] = sext <2 x i1> [[TMP1]] to <2 x i8>
-; CHECK-NEXT:    ret <2 x i8> [[NEG]]
+; CHECK-NEXT:    [[DIV_NEG:%.*]] = sext <2 x i1> [[TMP1]] to <2 x i8>
+; CHECK-NEXT:    ret <2 x i8> [[DIV_NEG]]
 ;
   %div = sdiv <2 x i8> %x, <i8 -128, i8 -128>
   %neg = sub <2 x i8> zeroinitializer, %div
@@ -956,8 +956,8 @@
 
 define i32 @test_exact_nonsw_exact(i32 %x) {
 ; CHECK-LABEL: @test_exact_nonsw_exact(
-; CHECK-NEXT:    [[NEG:%.*]] = sdiv exact i32 [[X:%.*]], -3
-; CHECK-NEXT:    ret i32 [[NEG]]
+; CHECK-NEXT:    [[DIV_NEG:%.*]] = sdiv exact i32 [[X:%.*]], -3
+; CHECK-NEXT:    ret i32 [[DIV_NEG]]
 ;
   %div = sdiv exact i32 %x, 3
   %neg = sub i32 0, %div
@@ -966,8 +966,8 @@
 
 define i32 @test_exact_nsw_noexact(i32 %x) {
 ; CHECK-LABEL: @test_exact_nsw_noexact(
-; CHECK-NEXT:    [[NEG:%.*]] = sdiv i32 [[X:%.*]], -3
-; CHECK-NEXT:    ret i32 [[NEG]]
+; CHECK-NEXT:    [[DIV_NEG:%.*]] = sdiv i32 [[X:%.*]], -3
+; CHECK-NEXT:    ret i32 [[DIV_NEG]]
 ;
   %div = sdiv i32 %x, 3
   %neg = sub nsw i32 0, %div
@@ -976,8 +976,8 @@
 
 define i32 @test_exact_nonsw_noexact(i32 %x) {
 ; CHECK-LABEL: @test_exact_nonsw_noexact(
-; CHECK-NEXT:    [[NEG:%.*]] = sdiv i32 [[X:%.*]], -3
-; CHECK-NEXT:    ret i32 [[NEG]]
+; CHECK-NEXT:    [[DIV_NEG:%.*]] = sdiv i32 [[X:%.*]], -3
+; CHECK-NEXT:    ret i32 [[DIV_NEG]]
 ;
   %div = sdiv i32 %x, 3
   %neg = sub i32 0, %div
@@ -1008,8 +1008,8 @@
 define i8 @test_exact_div_minSigned(i8 %x) {
 ; CHECK-LABEL: @test_exact_div_minSigned(
 ; CHECK-NEXT:    [[TMP1:%.*]] = icmp eq i8 [[X:%.*]], -128
-; CHECK-NEXT:    [[NEG:%.*]] = sext i1 [[TMP1]] to i8
-; CHECK-NEXT:    ret i8 [[NEG]]
+; CHECK-NEXT:    [[DIV_NEG:%.*]] = sext i1 [[TMP1]] to i8
+; CHECK-NEXT:    ret i8 [[DIV_NEG]]
 ;
   %div = sdiv exact i8 %x, -128
   %neg = sub nsw i8 0, %div
@@ -1040,7 +1040,7 @@
 
 define <2 x i8> @sdiv_by_int_min_vec_splat_undef(<2 x i8> %x) {
 ; CHECK-LABEL: @sdiv_by_int_min_vec_splat_undef(
-; CHECK-NEXT:    ret <2 x i8> undef
+; CHECK-NEXT:    ret <2 x i8> poison
 ;
   %d = sdiv <2 x i8> %x, <i8 -128, i8 undef>
   ret <2 x i8> %d
diff --git a/llvm/test/Transforms/InstCombine/icmp-div-constant.ll b/llvm/test/Transforms/InstCombine/icmp-div-constant.ll
--- a/llvm/test/Transforms/InstCombine/icmp-div-constant.ll
+++ b/llvm/test/Transforms/InstCombine/icmp-div-constant.ll
@@ -119,10 +119,10 @@
 ; CHECK-NEXT:    br i1 [[TOBOOL]], label [[THEN:%.*]], label [[EXIT:%.*]]
 ; CHECK:       then:
 ; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i16 [[C:%.*]], 0
-; CHECK-NEXT:    [[PHITMP1:%.*]] = sext i1 [[CMP]] to i32
+; CHECK-NEXT:    [[PHI_BO:%.*]] = sext i1 [[CMP]] to i32
 ; CHECK-NEXT:    br label [[EXIT]]
 ; CHECK:       exit:
-; CHECK-NEXT:    [[PHI:%.*]] = phi i32 [ -1, [[ENTRY:%.*]] ], [ [[PHITMP1]], [[THEN]] ]
+; CHECK-NEXT:    [[PHI:%.*]] = phi i32 [ -1, [[ENTRY:%.*]] ], [ [[PHI_BO]], [[THEN]] ]
 ; CHECK-NEXT:    ret i32 [[PHI]]
 ;
 entry:
@@ -149,8 +149,7 @@
 ; CHECK:       then:
 ; CHECK-NEXT:    br label [[EXIT]]
 ; CHECK:       exit:
-; CHECK-NEXT:    [[PHI:%.*]] = phi i32 [ -1, [[ENTRY:%.*]] ], [ 0, [[THEN]] ]
-; CHECK-NEXT:    ret i32 [[PHI]]
+; CHECK-NEXT:    ret i32 -1
 ;
 entry:
   %tobool = icmp eq i16 %a, 0
@@ -175,10 +174,10 @@
 ; CHECK-NEXT:    br i1 [[TOBOOL]], label [[THEN:%.*]], label [[EXIT:%.*]]
 ; CHECK:       then:
 ; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i16 [[C:%.*]], 0
-; CHECK-NEXT:    [[PHITMP1:%.*]] = sext i1 [[CMP]] to i32
+; CHECK-NEXT:    [[PHI_BO:%.*]] = sext i1 [[CMP]] to i32
 ; CHECK-NEXT:    br label [[EXIT]]
 ; CHECK:       exit:
-; CHECK-NEXT:    [[PHI:%.*]] = phi i32 [ -1, [[ENTRY:%.*]] ], [ [[PHITMP1]], [[THEN]] ]
+; CHECK-NEXT:    [[PHI:%.*]] = phi i32 [ -1, [[ENTRY:%.*]] ], [ [[PHI_BO]], [[THEN]] ]
 ; CHECK-NEXT:    ret i32 [[PHI]]
 ;
 entry:
diff --git a/llvm/test/Transforms/InstCombine/inselt-binop-inseltpoison.ll b/llvm/test/Transforms/InstCombine/inselt-binop-inseltpoison.ll
--- a/llvm/test/Transforms/InstCombine/inselt-binop-inseltpoison.ll
+++ b/llvm/test/Transforms/InstCombine/inselt-binop-inseltpoison.ll
@@ -247,7 +247,7 @@
 
 define <2 x i8> @urem_constant_op1(i8 %x) {
 ; CHECK-LABEL: @urem_constant_op1(
-; CHECK-NEXT:    ret <2 x i8> undef
+; CHECK-NEXT:    ret <2 x i8> poison
 ;
   %ins = insertelement <2 x i8> poison, i8 %x, i32 1
   %bo = urem <2 x i8> %ins, <i8 undef, i8 2>
@@ -289,7 +289,7 @@
 
 define <2 x i8> @srem_constant_op1(i8 %x) {
 ; CHECK-LABEL: @srem_constant_op1(
-; CHECK-NEXT:    ret <2 x i8> undef
+; CHECK-NEXT:    ret <2 x i8> poison
 ;
   %ins = insertelement <2 x i8> poison, i8 %x, i32 1
   %bo = srem <2 x i8> %ins, <i8 undef, i8 2>
@@ -331,7 +331,7 @@
 
 define <2 x i8> @udiv_constant_op1(i8 %x) {
 ; CHECK-LABEL: @udiv_constant_op1(
-; CHECK-NEXT:    ret <2 x i8> undef
+; CHECK-NEXT:    ret <2 x i8> poison
 ;
   %ins = insertelement <2 x i8> poison, i8 %x, i32 1
   %bo = udiv <2 x i8> %ins, <i8 undef, i8 2>
@@ -373,7 +373,7 @@
 
 define <2 x i8> @sdiv_constant_op1(i8 %x) {
 ; CHECK-LABEL: @sdiv_constant_op1(
-; CHECK-NEXT:    ret <2 x i8> undef
+; CHECK-NEXT:    ret <2 x i8> poison
 ;
   %ins = insertelement <2 x i8> poison, i8 %x, i32 1
   %bo = sdiv exact <2 x i8> %ins, <i8 undef, i8 2>
diff --git a/llvm/test/Transforms/InstCombine/inselt-binop.ll b/llvm/test/Transforms/InstCombine/inselt-binop.ll
--- a/llvm/test/Transforms/InstCombine/inselt-binop.ll
+++ b/llvm/test/Transforms/InstCombine/inselt-binop.ll
@@ -247,7 +247,7 @@
 
 define <2 x i8> @urem_constant_op1(i8 %x) {
 ; CHECK-LABEL: @urem_constant_op1(
-; CHECK-NEXT:    ret <2 x i8> undef
+; CHECK-NEXT:    ret <2 x i8> poison
 ;
   %ins = insertelement <2 x i8> undef, i8 %x, i32 1
   %bo = urem <2 x i8> %ins, <i8 undef, i8 2>
@@ -289,7 +289,7 @@
 
 define <2 x i8> @srem_constant_op1(i8 %x) {
 ; CHECK-LABEL: @srem_constant_op1(
-; CHECK-NEXT:    ret <2 x i8> undef
+; CHECK-NEXT:    ret <2 x i8> poison
 ;
   %ins = insertelement <2 x i8> undef, i8 %x, i32 1
   %bo = srem <2 x i8> %ins, <i8 undef, i8 2>
@@ -331,7 +331,7 @@
 
 define <2 x i8> @udiv_constant_op1(i8 %x) {
 ; CHECK-LABEL: @udiv_constant_op1(
-; CHECK-NEXT:    ret <2 x i8> undef
+; CHECK-NEXT:    ret <2 x i8> poison
 ;
   %ins = insertelement <2 x i8> undef, i8 %x, i32 1
   %bo = udiv <2 x i8> %ins, <i8 undef, i8 2>
@@ -373,7 +373,7 @@
 
 define <2 x i8> @sdiv_constant_op1(i8 %x) {
 ; CHECK-LABEL: @sdiv_constant_op1(
-; CHECK-NEXT:    ret <2 x i8> undef
+; CHECK-NEXT:    ret <2 x i8> poison
 ;
   %ins = insertelement <2 x i8> undef, i8 %x, i32 1
   %bo = sdiv exact <2 x i8> %ins, <i8 undef, i8 2>
diff --git a/llvm/test/Transforms/InstCombine/rem.ll b/llvm/test/Transforms/InstCombine/rem.ll
--- a/llvm/test/Transforms/InstCombine/rem.ll
+++ b/llvm/test/Transforms/InstCombine/rem.ll
@@ -247,7 +247,7 @@
 
 define i32 @test6(i32 %A) {
 ; CHECK-LABEL: @test6(
-; CHECK-NEXT:    ret i32 undef
+; CHECK-NEXT:    ret i32 poison
 ;
   %B = srem i32 %A, 0	;; undef
   ret i32 %B
diff --git a/llvm/test/Transforms/InstCombine/sdiv-exact-by-negative-power-of-two.ll b/llvm/test/Transforms/InstCombine/sdiv-exact-by-negative-power-of-two.ll
--- a/llvm/test/Transforms/InstCombine/sdiv-exact-by-negative-power-of-two.ll
+++ b/llvm/test/Transforms/InstCombine/sdiv-exact-by-negative-power-of-two.ll
@@ -55,7 +55,7 @@
 
 define <2 x i8> @n4_vec_undef(<2 x i8> %x) {
 ; CHECK-LABEL: @n4_vec_undef(
-; CHECK-NEXT:    ret <2 x i8> undef
+; CHECK-NEXT:    ret <2 x i8> poison
 ;
   %div = sdiv exact <2 x i8> %x, <i8 -32, i8 undef>
   ret <2 x i8> %div
diff --git a/llvm/test/Transforms/InstCombine/sdiv-exact-by-power-of-two.ll b/llvm/test/Transforms/InstCombine/sdiv-exact-by-power-of-two.ll
--- a/llvm/test/Transforms/InstCombine/sdiv-exact-by-power-of-two.ll
+++ b/llvm/test/Transforms/InstCombine/sdiv-exact-by-power-of-two.ll
@@ -53,7 +53,7 @@
 
 define <2 x i8> @n5_vec_undef(<2 x i8> %x) {
 ; CHECK-LABEL: @n5_vec_undef(
-; CHECK-NEXT:    ret <2 x i8> undef
+; CHECK-NEXT:    ret <2 x i8> poison
 ;
   %div = sdiv exact <2 x i8> %x, <i8 32, i8 undef>
   ret <2 x i8> %div
diff --git a/llvm/test/Transforms/InstCombine/shift.ll b/llvm/test/Transforms/InstCombine/shift.ll
--- a/llvm/test/Transforms/InstCombine/shift.ll
+++ b/llvm/test/Transforms/InstCombine/shift.ll
@@ -662,7 +662,7 @@
 
 define <2 x i32> @test38_undef(<2 x i32> %x) nounwind readnone {
 ; CHECK-LABEL: @test38_undef(
-; CHECK-NEXT:    ret <2 x i32> undef
+; CHECK-NEXT:    ret <2 x i32> poison
 ;
   %rem = srem <2 x i32> %x, <i32 32, i32 undef>
   %shl = shl <2 x i32> <i32 1, i32 1>, %rem
diff --git a/llvm/test/Transforms/InstCombine/vector-udiv.ll b/llvm/test/Transforms/InstCombine/vector-udiv.ll
--- a/llvm/test/Transforms/InstCombine/vector-udiv.ll
+++ b/llvm/test/Transforms/InstCombine/vector-udiv.ll
@@ -42,7 +42,7 @@
 
 define <4 x i32> @test_v4i32_negconst_undef(<4 x i32> %a0) {
 ; CHECK-LABEL: @test_v4i32_negconst_undef(
-; CHECK-NEXT:    ret <4 x i32> undef
+; CHECK-NEXT:    ret <4 x i32> poison
 ;
   %1 = udiv <4 x i32> %a0, <i32 -3, i32 -5, i32 -7, i32 undef>
   ret <4 x i32> %1
diff --git a/llvm/test/Transforms/InstCombine/vector-urem.ll b/llvm/test/Transforms/InstCombine/vector-urem.ll
--- a/llvm/test/Transforms/InstCombine/vector-urem.ll
+++ b/llvm/test/Transforms/InstCombine/vector-urem.ll
@@ -21,7 +21,7 @@
 
 define <4 x i32> @test_v4i32_const_pow2_undef(<4 x i32> %a0) {
 ; CHECK-LABEL: @test_v4i32_const_pow2_undef(
-; CHECK-NEXT:    ret <4 x i32> undef
+; CHECK-NEXT:    ret <4 x i32> poison
 ;
   %1 = urem <4 x i32> %a0, <i32 1, i32 2, i32 4, i32 undef>
   ret <4 x i32> %1
@@ -71,7 +71,7 @@
 
 define <4 x i32> @test_v4i32_negconst_undef(<4 x i32> %a0) {
 ; CHECK-LABEL: @test_v4i32_negconst_undef(
-; CHECK-NEXT:    ret <4 x i32> undef
+; CHECK-NEXT:    ret <4 x i32> poison
 ;
   %1 = urem <4 x i32> %a0, <i32 -3, i32 -5, i32 -7, i32 undef>
   ret <4 x i32> %1
diff --git a/llvm/test/Transforms/InstSimplify/div.ll b/llvm/test/Transforms/InstSimplify/div.ll
--- a/llvm/test/Transforms/InstSimplify/div.ll
+++ b/llvm/test/Transforms/InstSimplify/div.ll
@@ -43,10 +43,9 @@
   ret <2 x i8> %div
 }
 
-; TODO: instsimplify should fold these to poison
 define <2 x i8> @sdiv_zero_elt_vec(<2 x i8> %x) {
 ; CHECK-LABEL: @sdiv_zero_elt_vec(
-; CHECK-NEXT:    ret <2 x i8> undef
+; CHECK-NEXT:    ret <2 x i8> poison
 ;
   %div = sdiv <2 x i8> %x, <i8 -42, i8 0>
   ret <2 x i8> %div
@@ -54,7 +53,7 @@
 
 define <2 x i8> @udiv_zero_elt_vec(<2 x i8> %x) {
 ; CHECK-LABEL: @udiv_zero_elt_vec(
-; CHECK-NEXT:    ret <2 x i8> undef
+; CHECK-NEXT:    ret <2 x i8> poison
 ;
   %div = udiv <2 x i8> %x, <i8 0, i8 42>
   ret <2 x i8> %div
@@ -62,7 +61,7 @@
 
 define <2 x i8> @sdiv_undef_elt_vec(<2 x i8> %x) {
 ; CHECK-LABEL: @sdiv_undef_elt_vec(
-; CHECK-NEXT:    ret <2 x i8> undef
+; CHECK-NEXT:    ret <2 x i8> poison
 ;
   %div = sdiv <2 x i8> %x, <i8 -42, i8 undef>
   ret <2 x i8> %div
@@ -70,7 +69,7 @@
 
 define <2 x i8> @udiv_undef_elt_vec(<2 x i8> %x) {
 ; CHECK-LABEL: @udiv_undef_elt_vec(
-; CHECK-NEXT:    ret <2 x i8> undef
+; CHECK-NEXT:    ret <2 x i8> poison
 ;
   %div = udiv <2 x i8> %x, <i8 undef, i8 42>
   ret <2 x i8> %div
@@ -202,7 +201,6 @@
   ret i8 %v
 }
 
-; TODO: these should be poison
 define i32 @poison(i32 %x) {
 ; CHECK-LABEL: @poison(
 ; CHECK-NEXT:    ret i32 poison
@@ -211,6 +209,7 @@
   ret i32 %v
 }
 
+; TODO: this should be poison
 define i32 @poison2(i32 %x) {
 ; CHECK-LABEL: @poison2(
 ; CHECK-NEXT:    ret i32 0
@@ -221,7 +220,7 @@
 
 define <2 x i32> @poison3(<2 x i32> %x) {
 ; CHECK-LABEL: @poison3(
-; CHECK-NEXT:    ret <2 x i32> undef
+; CHECK-NEXT:    ret <2 x i32> poison
 ;
   %v = udiv <2 x i32> %x, <i32 poison, i32 1>
   ret <2 x i32> %v
diff --git a/llvm/test/Transforms/InstSimplify/rem.ll b/llvm/test/Transforms/InstSimplify/rem.ll
--- a/llvm/test/Transforms/InstSimplify/rem.ll
+++ b/llvm/test/Transforms/InstSimplify/rem.ll
@@ -43,10 +43,9 @@
   ret <2 x i8> %rem
 }
 
-; TODO: instsimplify should fold these to poison
 define <2 x i8> @srem_zero_elt_vec(<2 x i8> %x) {
 ; CHECK-LABEL: @srem_zero_elt_vec(
-; CHECK-NEXT:    ret <2 x i8> undef
+; CHECK-NEXT:    ret <2 x i8> poison
 ;
   %rem = srem <2 x i8> %x, <i8 -42, i8 0>
   ret <2 x i8> %rem
@@ -54,7 +53,7 @@
 
 define <2 x i8> @urem_zero_elt_vec(<2 x i8> %x) {
 ; CHECK-LABEL: @urem_zero_elt_vec(
-; CHECK-NEXT:    ret <2 x i8> undef
+; CHECK-NEXT:    ret <2 x i8> poison
 ;
   %rem = urem <2 x i8> %x, <i8 0, i8 42>
   ret <2 x i8> %rem
@@ -62,7 +61,7 @@
 
 define <2 x i8> @srem_undef_elt_vec(<2 x i8> %x) {
 ; CHECK-LABEL: @srem_undef_elt_vec(
-; CHECK-NEXT:    ret <2 x i8> undef
+; CHECK-NEXT:    ret <2 x i8> poison
 ;
   %rem = srem <2 x i8> %x, <i8 -42, i8 undef>
   ret <2 x i8> %rem
@@ -70,7 +69,7 @@
 
 define <2 x i8> @urem_undef_elt_vec(<2 x i8> %x) {
 ; CHECK-LABEL: @urem_undef_elt_vec(
-; CHECK-NEXT:    ret <2 x i8> undef
+; CHECK-NEXT:    ret <2 x i8> poison
 ;
   %rem = urem <2 x i8> %x, <i8 undef, i8 42>
   ret <2 x i8> %rem
diff --git a/llvm/test/Transforms/InstSimplify/undef.ll b/llvm/test/Transforms/InstSimplify/undef.ll
--- a/llvm/test/Transforms/InstSimplify/undef.ll
+++ b/llvm/test/Transforms/InstSimplify/undef.ll
@@ -188,7 +188,7 @@
 
 define i32 @test20(i32 %a) {
 ; CHECK-LABEL: @test20(
-; CHECK-NEXT:    ret i32 undef
+; CHECK-NEXT:    ret i32 poison
 ;
   %b = udiv i32 %a, 0
   ret i32 %b
@@ -196,7 +196,7 @@
 
 define <2 x i32> @test20vec(<2 x i32> %a) {
 ; CHECK-LABEL: @test20vec(
-; CHECK-NEXT:    ret <2 x i32> undef
+; CHECK-NEXT:    ret <2 x i32> poison
 ;
   %b = udiv <2 x i32> %a, zeroinitializer
   ret <2 x i32> %b
@@ -204,7 +204,7 @@
 
 define i32 @test21(i32 %a) {
 ; CHECK-LABEL: @test21(
-; CHECK-NEXT:    ret i32 undef
+; CHECK-NEXT:    ret i32 poison
 ;
   %b = sdiv i32 %a, 0
   ret i32 %b
@@ -212,7 +212,7 @@
 
 define <2 x i32> @test21vec(<2 x i32> %a) {
 ; CHECK-LABEL: @test21vec(
-; CHECK-NEXT:    ret <2 x i32> undef
+; CHECK-NEXT:    ret <2 x i32> poison
 ;
   %b = sdiv <2 x i32> %a, zeroinitializer
   ret <2 x i32> %b
@@ -348,7 +348,7 @@
 
 define i32 @test38(i32 %a) {
 ; CHECK-LABEL: @test38(
-; CHECK-NEXT:    ret i32 undef
+; CHECK-NEXT:    ret i32 poison
 ;
   %b = udiv i32 %a, undef
   ret i32 %b
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
@@ -425,7 +425,7 @@
 ; 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 undef, i32 poison, i32 poison, i32 poison>, i32 [[AB1]], i32 1
+; 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