diff --git a/llvm/test/Transforms/SLPVectorizer/X86/diamond_broadcast_extra_shuffle.ll b/llvm/test/Transforms/SLPVectorizer/X86/diamond_broadcast_extra_shuffle.ll
--- a/llvm/test/Transforms/SLPVectorizer/X86/diamond_broadcast_extra_shuffle.ll
+++ b/llvm/test/Transforms/SLPVectorizer/X86/diamond_broadcast_extra_shuffle.ll
@@ -28,6 +28,33 @@
   ret i32 0
 }
 
+define i32 @diamond_broadcast_poison(i32* noalias nocapture %B, i32* noalias nocapture %A) {
+; CHECK-LABEL: @diamond_broadcast_poison(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[LD:%.*]] = load i32, i32* [[A:%.*]], align 4
+; CHECK-NEXT:    [[TMP0:%.*]] = insertelement <4 x i32> poison, i32 [[LD]], i32 0
+; CHECK-NEXT:    [[SHUFFLE:%.*]] = shufflevector <4 x i32> [[TMP0]], <4 x i32> poison, <4 x i32> zeroinitializer
+; CHECK-NEXT:    [[TMP1:%.*]] = mul <4 x i32> [[SHUFFLE]], [[SHUFFLE]]
+; CHECK-NEXT:    [[TMP2:%.*]] = bitcast i32* [[B:%.*]] to <4 x i32>*
+; CHECK-NEXT:    store <4 x i32> [[TMP1]], <4 x i32>* [[TMP2]], align 4
+; CHECK-NEXT:    ret i32 0
+;
+entry:
+  %ld = load i32, i32* %A, align 4
+  %mul = mul i32 %ld, %ld
+  store i32 %mul, i32* %B, align 4
+  %mul8 = mul i32 %ld, %ld
+  %arrayidx9 = getelementptr inbounds i32, i32* %B, i64 1
+  store i32 %mul8, i32* %arrayidx9, align 4
+  %mul14 = mul i32 %ld, %ld
+  %arrayidx15 = getelementptr inbounds i32, i32* %B, i64 2
+  store i32 %mul14, i32* %arrayidx15, align 4
+  %mul20 = mul i32 %ld, poison
+  %arrayidx21 = getelementptr inbounds i32, i32* %B, i64 3
+  store i32 %mul20, i32* %arrayidx21, align 4
+  ret i32 0
+}
+
 define i32 @diamond_broadcast2(i32* noalias nocapture %B, i32* noalias nocapture %A) {
 ; CHECK-LABEL: @diamond_broadcast2(
 ; CHECK-NEXT:  entry:
@@ -55,6 +82,33 @@
   ret i32 0
 }
 
+define i32 @diamond_broadcast2_poison(i32* noalias nocapture %B, i32* noalias nocapture %A) {
+; CHECK-LABEL: @diamond_broadcast2_poison(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[LD:%.*]] = load i32, i32* [[A:%.*]], align 4
+; CHECK-NEXT:    [[TMP0:%.*]] = insertelement <4 x i32> poison, i32 [[LD]], i32 0
+; CHECK-NEXT:    [[SHUFFLE:%.*]] = shufflevector <4 x i32> [[TMP0]], <4 x i32> poison, <4 x i32> zeroinitializer
+; CHECK-NEXT:    [[TMP1:%.*]] = mul <4 x i32> [[SHUFFLE]], [[SHUFFLE]]
+; CHECK-NEXT:    [[TMP2:%.*]] = bitcast i32* [[B:%.*]] to <4 x i32>*
+; CHECK-NEXT:    store <4 x i32> [[TMP1]], <4 x i32>* [[TMP2]], align 4
+; CHECK-NEXT:    ret i32 0
+;
+entry:
+  %ld = load i32, i32* %A, align 4
+  %mul = mul i32 %ld, %ld
+  store i32 %mul, i32* %B, align 4
+  %mul8 = mul i32 %ld, %ld
+  %arrayidx9 = getelementptr inbounds i32, i32* %B, i64 1
+  store i32 %mul8, i32* %arrayidx9, align 4
+  %mul14 = mul i32 %ld, %ld
+  %arrayidx15 = getelementptr inbounds i32, i32* %B, i64 2
+  store i32 %mul14, i32* %arrayidx15, align 4
+  %mul20 = mul i32 poison, %ld
+  %arrayidx21 = getelementptr inbounds i32, i32* %B, i64 3
+  store i32 %mul20, i32* %arrayidx21, align 4
+  ret i32 0
+}
+
 define i32 @diamond_broadcast3(i32* noalias nocapture %B, i32* noalias nocapture %A) {
 ; CHECK-LABEL: @diamond_broadcast3(
 ; CHECK-NEXT:  entry:
@@ -82,3 +136,30 @@
   ret i32 0
 }
 
+define i32 @diamond_broadcast3_poison(i32* noalias nocapture %B, i32* noalias nocapture %A) {
+; CHECK-LABEL: @diamond_broadcast3_poison(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[LD:%.*]] = load i32, i32* [[A:%.*]], align 4
+; CHECK-NEXT:    [[TMP0:%.*]] = insertelement <4 x i32> poison, i32 [[LD]], i32 0
+; CHECK-NEXT:    [[SHUFFLE:%.*]] = shufflevector <4 x i32> [[TMP0]], <4 x i32> poison, <4 x i32> zeroinitializer
+; CHECK-NEXT:    [[TMP1:%.*]] = mul <4 x i32> [[SHUFFLE]], [[SHUFFLE]]
+; CHECK-NEXT:    [[TMP2:%.*]] = bitcast i32* [[B:%.*]] to <4 x i32>*
+; CHECK-NEXT:    store <4 x i32> [[TMP1]], <4 x i32>* [[TMP2]], align 4
+; CHECK-NEXT:    ret i32 0
+;
+entry:
+  %ld = load i32, i32* %A, align 4
+  %mul = mul i32 %ld, %ld
+  store i32 %mul, i32* %B, align 4
+  %mul8 = mul i32 %ld, %ld
+  %arrayidx9 = getelementptr inbounds i32, i32* %B, i64 1
+  store i32 %mul8, i32* %arrayidx9, align 4
+  %mul14 = mul i32 %ld, poison
+  %arrayidx15 = getelementptr inbounds i32, i32* %B, i64 2
+  store i32 %mul14, i32* %arrayidx15, align 4
+  %mul20 = mul i32 poison, %ld
+  %arrayidx21 = getelementptr inbounds i32, i32* %B, i64 3
+  store i32 %mul20, i32* %arrayidx21, align 4
+  ret i32 0
+}
+
diff --git a/llvm/test/Transforms/SLPVectorizer/X86/phi-undef-input.ll b/llvm/test/Transforms/SLPVectorizer/X86/phi-undef-input.ll
new file mode 100644
--- /dev/null
+++ b/llvm/test/Transforms/SLPVectorizer/X86/phi-undef-input.ll
@@ -0,0 +1,228 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt < %s -slp-vectorizer -slp-threshold=-1000 -mtriple=x86_64 -S | FileCheck %s
+
+; The inputs to vector phi should remain undef.
+
+define i32 @phi3UndefInput(i1 %cond, i8 %arg0, i8 %arg1, i8 %arg2, i8 %arg3, i32* %ptr) {
+; CHECK-LABEL: @phi3UndefInput(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    br i1 [[COND:%.*]], label [[BB2:%.*]], label [[BB3:%.*]]
+; CHECK:       bb2:
+; CHECK-NEXT:    [[TMP0:%.*]] = insertelement <4 x i8> poison, i8 [[ARG0:%.*]], i32 0
+; CHECK-NEXT:    [[TMP1:%.*]] = insertelement <4 x i8> [[TMP0]], i8 [[ARG1:%.*]], i32 1
+; CHECK-NEXT:    [[TMP2:%.*]] = insertelement <4 x i8> [[TMP1]], i8 [[ARG2:%.*]], i32 2
+; CHECK-NEXT:    [[TMP3:%.*]] = insertelement <4 x i8> [[TMP2]], i8 [[ARG3:%.*]], i32 3
+; CHECK-NEXT:    br label [[BB3]]
+; CHECK:       bb3:
+; CHECK-NEXT:    [[TMP4:%.*]] = phi <4 x i8> [ [[TMP3]], [[BB2]] ], [ <i8 0, i8 poison, i8 poison, i8 poison>, [[ENTRY:%.*]] ]
+; CHECK-NEXT:    [[TMP5:%.*]] = zext <4 x i8> [[TMP4]] to <4 x i32>
+; CHECK-NEXT:    [[TMP6:%.*]] = call i32 @llvm.vector.reduce.or.v4i32(<4 x i32> [[TMP5]])
+; CHECK-NEXT:    ret i32 [[TMP6]]
+;
+entry:
+  br i1 %cond, label %bb2, label %bb3
+
+bb2:
+  br label %bb3
+
+bb3:
+  %phi0 = phi i8 [ %arg0, %bb2 ], [ 0, %entry ]
+  %phi1 = phi i8 [ %arg1, %bb2 ], [ undef, %entry ]
+  %phi2 = phi i8 [ %arg2, %bb2 ], [ undef, %entry ]
+  %phi3 = phi i8 [ %arg3, %bb2 ], [ undef, %entry ]
+  %zext0 = zext i8 %phi0 to i32
+  %zext1 = zext i8 %phi1 to i32
+  %zext2 = zext i8 %phi2 to i32
+  %zext3 = zext i8 %phi3 to i32
+  %or1 = or i32 %zext0, %zext1
+  %or2 = or i32 %or1, %zext2
+  %or3 = or i32 %or2, %zext3
+  ret i32 %or3
+}
+
+define i32 @phi2UndefInput(i1 %cond, i8 %arg0, i8 %arg1, i8 %arg2, i8 %arg3, i32* %ptr) {
+; CHECK-LABEL: @phi2UndefInput(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    br i1 [[COND:%.*]], label [[BB2:%.*]], label [[BB3:%.*]]
+; CHECK:       bb2:
+; CHECK-NEXT:    [[TMP0:%.*]] = insertelement <4 x i8> poison, i8 [[ARG0:%.*]], i32 0
+; CHECK-NEXT:    [[TMP1:%.*]] = insertelement <4 x i8> [[TMP0]], i8 [[ARG1:%.*]], i32 1
+; CHECK-NEXT:    [[TMP2:%.*]] = insertelement <4 x i8> [[TMP1]], i8 [[ARG2:%.*]], i32 2
+; CHECK-NEXT:    [[TMP3:%.*]] = insertelement <4 x i8> [[TMP2]], i8 [[ARG3:%.*]], i32 3
+; CHECK-NEXT:    br label [[BB3]]
+; CHECK:       bb3:
+; CHECK-NEXT:    [[TMP4:%.*]] = phi <4 x i8> [ [[TMP3]], [[BB2]] ], [ <i8 0, i8 0, i8 poison, i8 poison>, [[ENTRY:%.*]] ]
+; CHECK-NEXT:    [[TMP5:%.*]] = zext <4 x i8> [[TMP4]] to <4 x i32>
+; CHECK-NEXT:    [[TMP6:%.*]] = call i32 @llvm.vector.reduce.or.v4i32(<4 x i32> [[TMP5]])
+; CHECK-NEXT:    ret i32 [[TMP6]]
+;
+entry:
+  br i1 %cond, label %bb2, label %bb3
+
+bb2:
+  br label %bb3
+
+bb3:
+  %phi0 = phi i8 [ %arg0, %bb2 ], [ 0, %entry ]
+  %phi1 = phi i8 [ %arg1, %bb2 ], [ 0, %entry ]
+  %phi2 = phi i8 [ %arg2, %bb2 ], [ undef, %entry ]
+  %phi3 = phi i8 [ %arg3, %bb2 ], [ undef, %entry ]
+  %zext0 = zext i8 %phi0 to i32
+  %zext1 = zext i8 %phi1 to i32
+  %zext2 = zext i8 %phi2 to i32
+  %zext3 = zext i8 %phi3 to i32
+  %or1 = or i32 %zext0, %zext1
+  %or2 = or i32 %or1, %zext2
+  %or3 = or i32 %or2, %zext3
+  ret i32 %or3
+}
+
+define i32 @phi1UndefInput(i1 %cond, i8 %arg0, i8 %arg1, i8 %arg2, i8 %arg3, i32* %ptr) {
+; CHECK-LABEL: @phi1UndefInput(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    br i1 [[COND:%.*]], label [[BB2:%.*]], label [[BB3:%.*]]
+; CHECK:       bb2:
+; CHECK-NEXT:    [[TMP0:%.*]] = insertelement <4 x i8> poison, i8 [[ARG0:%.*]], i32 0
+; CHECK-NEXT:    [[TMP1:%.*]] = insertelement <4 x i8> [[TMP0]], i8 [[ARG1:%.*]], i32 1
+; CHECK-NEXT:    [[TMP2:%.*]] = insertelement <4 x i8> [[TMP1]], i8 [[ARG2:%.*]], i32 2
+; CHECK-NEXT:    [[TMP3:%.*]] = insertelement <4 x i8> [[TMP2]], i8 [[ARG3:%.*]], i32 3
+; CHECK-NEXT:    br label [[BB3]]
+; CHECK:       bb3:
+; CHECK-NEXT:    [[TMP4:%.*]] = phi <4 x i8> [ [[TMP3]], [[BB2]] ], [ <i8 0, i8 0, i8 0, i8 poison>, [[ENTRY:%.*]] ]
+; CHECK-NEXT:    [[TMP5:%.*]] = zext <4 x i8> [[TMP4]] to <4 x i32>
+; CHECK-NEXT:    [[TMP6:%.*]] = call i32 @llvm.vector.reduce.or.v4i32(<4 x i32> [[TMP5]])
+; CHECK-NEXT:    ret i32 [[TMP6]]
+;
+entry:
+  br i1 %cond, label %bb2, label %bb3
+
+bb2:
+  br label %bb3
+
+bb3:
+  %phi0 = phi i8 [ %arg0, %bb2 ], [ 0, %entry ]
+  %phi1 = phi i8 [ %arg1, %bb2 ], [ 0, %entry ]
+  %phi2 = phi i8 [ %arg2, %bb2 ], [ 0, %entry ]
+  %phi3 = phi i8 [ %arg3, %bb2 ], [ undef, %entry ]
+  %zext0 = zext i8 %phi0 to i32
+  %zext1 = zext i8 %phi1 to i32
+  %zext2 = zext i8 %phi2 to i32
+  %zext3 = zext i8 %phi3 to i32
+  %or1 = or i32 %zext0, %zext1
+  %or2 = or i32 %or1, %zext2
+  %or3 = or i32 %or2, %zext3
+  ret i32 %or3
+}
+
+
+define i32 @phi1Undef1PoisonInput(i1 %cond, i8 %arg0, i8 %arg1, i8 %arg2, i8 %arg3, i32* %ptr) {
+; CHECK-LABEL: @phi1Undef1PoisonInput(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    br i1 [[COND:%.*]], label [[BB2:%.*]], label [[BB3:%.*]]
+; CHECK:       bb2:
+; CHECK-NEXT:    [[TMP0:%.*]] = insertelement <4 x i8> poison, i8 [[ARG0:%.*]], i32 0
+; CHECK-NEXT:    [[TMP1:%.*]] = insertelement <4 x i8> [[TMP0]], i8 [[ARG1:%.*]], i32 1
+; CHECK-NEXT:    [[TMP2:%.*]] = insertelement <4 x i8> [[TMP1]], i8 [[ARG2:%.*]], i32 2
+; CHECK-NEXT:    [[TMP3:%.*]] = insertelement <4 x i8> [[TMP2]], i8 [[ARG3:%.*]], i32 3
+; CHECK-NEXT:    br label [[BB3]]
+; CHECK:       bb3:
+; CHECK-NEXT:    [[TMP4:%.*]] = phi <4 x i8> [ [[TMP3]], [[BB2]] ], [ <i8 0, i8 0, i8 poison, i8 poison>, [[ENTRY:%.*]] ]
+; CHECK-NEXT:    [[TMP5:%.*]] = zext <4 x i8> [[TMP4]] to <4 x i32>
+; CHECK-NEXT:    [[TMP6:%.*]] = call i32 @llvm.vector.reduce.or.v4i32(<4 x i32> [[TMP5]])
+; CHECK-NEXT:    ret i32 [[TMP6]]
+;
+entry:
+  br i1 %cond, label %bb2, label %bb3
+
+bb2:
+  br label %bb3
+
+bb3:
+  %phi0 = phi i8 [ %arg0, %bb2 ], [ 0, %entry ]
+  %phi1 = phi i8 [ %arg1, %bb2 ], [ 0, %entry ]
+  %phi2 = phi i8 [ %arg2, %bb2 ], [ poison, %entry ]
+  %phi3 = phi i8 [ %arg3, %bb2 ], [ undef, %entry ]
+  %zext0 = zext i8 %phi0 to i32
+  %zext1 = zext i8 %phi1 to i32
+  %zext2 = zext i8 %phi2 to i32
+  %zext3 = zext i8 %phi3 to i32
+  %or1 = or i32 %zext0, %zext1
+  %or2 = or i32 %or1, %zext2
+  %or3 = or i32 %or2, %zext3
+  ret i32 %or3
+}
+
+
+define i32 @phi1Undef2PoisonInputs(i1 %cond, i8 %arg0, i8 %arg1, i8 %arg2, i8 %arg3, i32* %ptr) {
+; CHECK-LABEL: @phi1Undef2PoisonInputs(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    br i1 [[COND:%.*]], label [[BB2:%.*]], label [[BB3:%.*]]
+; CHECK:       bb2:
+; CHECK-NEXT:    [[TMP0:%.*]] = insertelement <4 x i8> poison, i8 [[ARG1:%.*]], i32 0
+; CHECK-NEXT:    [[TMP1:%.*]] = insertelement <4 x i8> [[TMP0]], i8 [[ARG0:%.*]], i32 1
+; CHECK-NEXT:    [[TMP2:%.*]] = insertelement <4 x i8> [[TMP1]], i8 [[ARG2:%.*]], i32 2
+; CHECK-NEXT:    [[TMP3:%.*]] = insertelement <4 x i8> [[TMP2]], i8 [[ARG3:%.*]], i32 3
+; CHECK-NEXT:    br label [[BB3]]
+; CHECK:       bb3:
+; CHECK-NEXT:    [[TMP4:%.*]] = phi <4 x i8> [ [[TMP3]], [[BB2]] ], [ <i8 0, i8 poison, i8 poison, i8 poison>, [[ENTRY:%.*]] ]
+; CHECK-NEXT:    [[TMP5:%.*]] = zext <4 x i8> [[TMP4]] to <4 x i32>
+; CHECK-NEXT:    [[TMP6:%.*]] = call i32 @llvm.vector.reduce.or.v4i32(<4 x i32> [[TMP5]])
+; CHECK-NEXT:    ret i32 [[TMP6]]
+;
+entry:
+  br i1 %cond, label %bb2, label %bb3
+
+bb2:
+  br label %bb3
+
+bb3:
+  %phi0 = phi i8 [ %arg0, %bb2 ], [ poison, %entry ]
+  %phi1 = phi i8 [ %arg1, %bb2 ], [ 0, %entry ]
+  %phi2 = phi i8 [ %arg2, %bb2 ], [ poison, %entry ]
+  %phi3 = phi i8 [ %arg3, %bb2 ], [ undef, %entry ]
+  %zext0 = zext i8 %phi0 to i32
+  %zext1 = zext i8 %phi1 to i32
+  %zext2 = zext i8 %phi2 to i32
+  %zext3 = zext i8 %phi3 to i32
+  %or1 = or i32 %zext0, %zext1
+  %or2 = or i32 %or1, %zext2
+  %or3 = or i32 %or2, %zext3
+  ret i32 %or3
+}
+
+define i32 @phi1Undef1PoisonGapInput(i1 %cond, i8 %arg0, i8 %arg1, i8 %arg2, i8 %arg3, i32* %ptr) {
+; CHECK-LABEL: @phi1Undef1PoisonGapInput(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    br i1 [[COND:%.*]], label [[BB2:%.*]], label [[BB3:%.*]]
+; CHECK:       bb2:
+; CHECK-NEXT:    [[TMP0:%.*]] = insertelement <4 x i8> poison, i8 [[ARG1:%.*]], i32 0
+; CHECK-NEXT:    [[TMP1:%.*]] = insertelement <4 x i8> [[TMP0]], i8 [[ARG3:%.*]], i32 1
+; CHECK-NEXT:    [[TMP2:%.*]] = insertelement <4 x i8> [[TMP1]], i8 [[ARG0:%.*]], i32 2
+; CHECK-NEXT:    [[TMP3:%.*]] = insertelement <4 x i8> [[TMP2]], i8 [[ARG2:%.*]], i32 3
+; CHECK-NEXT:    br label [[BB3]]
+; CHECK:       bb3:
+; CHECK-NEXT:    [[TMP4:%.*]] = phi <4 x i8> [ [[TMP3]], [[BB2]] ], [ <i8 0, i8 0, i8 poison, i8 poison>, [[ENTRY:%.*]] ]
+; CHECK-NEXT:    [[TMP5:%.*]] = zext <4 x i8> [[TMP4]] to <4 x i32>
+; CHECK-NEXT:    [[TMP6:%.*]] = call i32 @llvm.vector.reduce.or.v4i32(<4 x i32> [[TMP5]])
+; CHECK-NEXT:    ret i32 [[TMP6]]
+;
+entry:
+  br i1 %cond, label %bb2, label %bb3
+
+bb2:
+  br label %bb3
+
+bb3:
+  %phi0 = phi i8 [ %arg0, %bb2 ], [ poison, %entry ]
+  %phi1 = phi i8 [ %arg1, %bb2 ], [ 0, %entry ]
+  %phi2 = phi i8 [ %arg2, %bb2 ], [ undef, %entry ]
+  %phi3 = phi i8 [ %arg3, %bb2 ], [ 0, %entry ]
+  %zext0 = zext i8 %phi0 to i32
+  %zext1 = zext i8 %phi1 to i32
+  %zext2 = zext i8 %phi2 to i32
+  %zext3 = zext i8 %phi3 to i32
+  %or1 = or i32 %zext0, %zext1
+  %or2 = or i32 %or1, %zext2
+  %or3 = or i32 %or2, %zext3
+  ret i32 %or3
+}