diff --git a/llvm/test/Transforms/SLPVectorizer/X86/phi-unreachable-input-block.ll b/llvm/test/Transforms/SLPVectorizer/X86/phi-unreachable-input-block.ll
new file mode 100644
--- /dev/null
+++ b/llvm/test/Transforms/SLPVectorizer/X86/phi-unreachable-input-block.ll
@@ -0,0 +1,112 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt < %s -slp-vectorizer -slp-threshold=-1000 -mtriple=x86_64-unknown-linux -S | FileCheck %s
+
+; If an input block to a phi node is unreachable from entry then its input
+; should be undef and not poison.
+; In the following tests bb2 is unreachable from entry, so any input to the phi
+; coming from there should be undef.
+
+define void @phiUndefInput(i64* %ptr, i8 %arg0, i8 %arg1) {
+; CHECK-LABEL: @phiUndefInput(
+; CHECK-NEXT:  bb1:
+; CHECK-NEXT:    [[TMP0:%.*]] = insertelement <2 x i8> poison, i8 [[ARG0:%.*]], i32 0
+; CHECK-NEXT:    [[TMP1:%.*]] = insertelement <2 x i8> [[TMP0]], i8 [[ARG1:%.*]], i32 1
+; CHECK-NEXT:    br label [[BB3:%.*]]
+; CHECK:       bb2:
+; CHECK-NEXT:    br label [[BB3]]
+; CHECK:       bb3:
+; CHECK-NEXT:    [[TMP2:%.*]] = phi <2 x i8> [ [[TMP1]], [[BB1:%.*]] ], [ poison, [[BB2:%.*]] ]
+; CHECK-NEXT:    [[TMP3:%.*]] = zext <2 x i8> [[TMP2]] to <2 x i64>
+; CHECK-NEXT:    [[GEP0:%.*]] = getelementptr i64, i64* [[PTR:%.*]], i64 0
+; CHECK-NEXT:    [[TMP4:%.*]] = bitcast i64* [[GEP0]] to <2 x i64>*
+; CHECK-NEXT:    store <2 x i64> [[TMP3]], <2 x i64>* [[TMP4]], align 4
+; CHECK-NEXT:    ret void
+;
+bb1:
+  br label %bb3
+
+bb2:
+  br label %bb3
+
+bb3:
+  %phi0 = phi i8 [ %arg0, %bb1 ], [ undef, %bb2 ]
+  %phi1 = phi i8 [ %arg1, %bb1 ], [ 0, %bb2 ]
+  %zext0 = zext i8 %phi0 to i64
+  %zext1 = zext i8 %phi1 to i64
+  %gep0 = getelementptr i64, i64* %ptr, i64 0
+  %gep1 = getelementptr i64, i64* %ptr, i64 1
+  store i64 %zext0, i64* %gep0
+  store i64 %zext1, i64* %gep1
+  ret void
+}
+
+
+define void @phiConstInput(i64* %ptr, i8 %arg0, i8 %arg1) {
+; CHECK-LABEL: @phiConstInput(
+; CHECK-NEXT:  bb1:
+; CHECK-NEXT:    [[TMP0:%.*]] = insertelement <2 x i8> poison, i8 [[ARG0:%.*]], i32 0
+; CHECK-NEXT:    [[TMP1:%.*]] = insertelement <2 x i8> [[TMP0]], i8 [[ARG1:%.*]], i32 1
+; CHECK-NEXT:    br label [[BB3:%.*]]
+; CHECK:       bb2:
+; CHECK-NEXT:    br label [[BB3]]
+; CHECK:       bb3:
+; CHECK-NEXT:    [[TMP2:%.*]] = phi <2 x i8> [ [[TMP1]], [[BB1:%.*]] ], [ poison, [[BB2:%.*]] ]
+; CHECK-NEXT:    [[TMP3:%.*]] = zext <2 x i8> [[TMP2]] to <2 x i64>
+; CHECK-NEXT:    [[GEP0:%.*]] = getelementptr i64, i64* [[PTR:%.*]], i64 0
+; CHECK-NEXT:    [[TMP4:%.*]] = bitcast i64* [[GEP0]] to <2 x i64>*
+; CHECK-NEXT:    store <2 x i64> [[TMP3]], <2 x i64>* [[TMP4]], align 4
+; CHECK-NEXT:    ret void
+;
+bb1:
+  br label %bb3
+
+bb2:
+  br label %bb3
+
+bb3:
+  %phi0 = phi i8 [ %arg0, %bb1 ], [ 1, %bb2 ]
+  %phi1 = phi i8 [ %arg1, %bb1 ], [ 0, %bb2 ]
+  %zext0 = zext i8 %phi0 to i64
+  %zext1 = zext i8 %phi1 to i64
+  %gep0 = getelementptr i64, i64* %ptr, i64 0
+  %gep1 = getelementptr i64, i64* %ptr, i64 1
+  store i64 %zext0, i64* %gep0
+  store i64 %zext1, i64* %gep1
+  ret void
+}
+
+
+define void @phiPoisonInput(i64* %ptr, i8 %arg0, i8 %arg1) {
+; CHECK-LABEL: @phiPoisonInput(
+; CHECK-NEXT:  bb1:
+; CHECK-NEXT:    [[TMP0:%.*]] = insertelement <2 x i8> poison, i8 [[ARG0:%.*]], i32 0
+; CHECK-NEXT:    [[TMP1:%.*]] = insertelement <2 x i8> [[TMP0]], i8 [[ARG1:%.*]], i32 1
+; CHECK-NEXT:    br label [[BB3:%.*]]
+; CHECK:       bb2:
+; CHECK-NEXT:    br label [[BB3]]
+; CHECK:       bb3:
+; CHECK-NEXT:    [[TMP2:%.*]] = phi <2 x i8> [ [[TMP1]], [[BB1:%.*]] ], [ poison, [[BB2:%.*]] ]
+; CHECK-NEXT:    [[TMP3:%.*]] = zext <2 x i8> [[TMP2]] to <2 x i64>
+; CHECK-NEXT:    [[GEP0:%.*]] = getelementptr i64, i64* [[PTR:%.*]], i64 0
+; CHECK-NEXT:    [[TMP4:%.*]] = bitcast i64* [[GEP0]] to <2 x i64>*
+; CHECK-NEXT:    store <2 x i64> [[TMP3]], <2 x i64>* [[TMP4]], align 4
+; CHECK-NEXT:    ret void
+;
+bb1:
+  br label %bb3
+
+bb2:
+  br label %bb3
+
+bb3:
+  %phi0 = phi i8 [ %arg0, %bb1 ], [ poison, %bb2 ]
+  %phi1 = phi i8 [ %arg1, %bb1 ], [ poison, %bb2 ]
+  %zext0 = zext i8 %phi0 to i64
+  %zext1 = zext i8 %phi1 to i64
+  %gep0 = getelementptr i64, i64* %ptr, i64 0
+  %gep1 = getelementptr i64, i64* %ptr, i64 1
+  store i64 %zext0, i64* %gep0
+  store i64 %zext1, i64* %gep1
+  ret void
+}
+