diff --git a/llvm/test/Transforms/PhaseOrdering/X86/vector-reduction-known-first-value.ll b/llvm/test/Transforms/PhaseOrdering/X86/vector-reduction-known-first-value.ll
new file mode 100644
index 0000000000000..508a501d9e847
--- /dev/null
+++ b/llvm/test/Transforms/PhaseOrdering/X86/vector-reduction-known-first-value.ll
@@ -0,0 +1,117 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt -S -O3 < %s | FileCheck %s
+
+target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+declare void @use(i8)
+
+define i16 @test(ptr %ptr) {
+; CHECK-LABEL: @test(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[FIRST:%.*]] = load i8, ptr [[PTR:%.*]], align 1
+; CHECK-NEXT:    tail call void @use(i8 [[FIRST]]) #[[ATTR2:[0-9]+]]
+; CHECK-NEXT:    [[VAL_EXT2:%.*]] = zext i8 [[FIRST]] to i16
+; CHECK-NEXT:    [[TMP0:%.*]] = insertelement <8 x i16> <i16 poison, i16 0, i16 0, i16 0, i16 0, i16 0, i16 0, i16 0>, i16 [[VAL_EXT2]], i64 0
+; CHECK-NEXT:    br label [[VECTOR_BODY:%.*]]
+; CHECK:       vector.body:
+; CHECK-NEXT:    [[INDEX:%.*]] = phi i64 [ 0, [[ENTRY:%.*]] ], [ [[INDEX_NEXT:%.*]], [[VECTOR_BODY]] ]
+; CHECK-NEXT:    [[VEC_PHI:%.*]] = phi <8 x i16> [ [[TMP0]], [[ENTRY]] ], [ [[TMP5:%.*]], [[VECTOR_BODY]] ]
+; CHECK-NEXT:    [[VEC_PHI5:%.*]] = phi <8 x i16> [ zeroinitializer, [[ENTRY]] ], [ [[TMP6:%.*]], [[VECTOR_BODY]] ]
+; CHECK-NEXT:    [[OFFSET_IDX:%.*]] = or i64 [[INDEX]], 1
+; CHECK-NEXT:    [[TMP1:%.*]] = getelementptr inbounds i8, ptr [[PTR]], i64 [[OFFSET_IDX]]
+; CHECK-NEXT:    [[WIDE_LOAD:%.*]] = load <8 x i8>, ptr [[TMP1]], align 1
+; CHECK-NEXT:    [[TMP2:%.*]] = getelementptr inbounds i8, ptr [[TMP1]], i64 8
+; CHECK-NEXT:    [[WIDE_LOAD6:%.*]] = load <8 x i8>, ptr [[TMP2]], align 1
+; CHECK-NEXT:    [[TMP3:%.*]] = zext <8 x i8> [[WIDE_LOAD]] to <8 x i16>
+; CHECK-NEXT:    [[TMP4:%.*]] = zext <8 x i8> [[WIDE_LOAD6]] to <8 x i16>
+; CHECK-NEXT:    [[TMP5]] = add <8 x i16> [[VEC_PHI]], [[TMP3]]
+; CHECK-NEXT:    [[TMP6]] = add <8 x i16> [[VEC_PHI5]], [[TMP4]]
+; CHECK-NEXT:    [[INDEX_NEXT]] = add nuw i64 [[INDEX]], 16
+; CHECK-NEXT:    [[TMP7:%.*]] = icmp eq i64 [[INDEX_NEXT]], 1008
+; CHECK-NEXT:    br i1 [[TMP7]], label [[LOOP_LOOP_CRIT_EDGE:%.*]], label [[VECTOR_BODY]], !llvm.loop [[LOOP0:![0-9]+]]
+; CHECK:       loop.loop_crit_edge:
+; CHECK-NEXT:    [[BIN_RDX:%.*]] = add <8 x i16> [[TMP6]], [[TMP5]]
+; CHECK-NEXT:    [[TMP8:%.*]] = call i16 @llvm.vector.reduce.add.v8i16(<8 x i16> [[BIN_RDX]])
+; CHECK-NEXT:    [[GEP_PHI_TRANS_INSERT:%.*]] = getelementptr inbounds i8, ptr [[PTR]], i64 1009
+; CHECK-NEXT:    [[VAL_PRE:%.*]] = load i8, ptr [[GEP_PHI_TRANS_INSERT]], align 1
+; CHECK-NEXT:    [[VAL_EXT:%.*]] = zext i8 [[VAL_PRE]] to i16
+; CHECK-NEXT:    [[ACCUM_NEXT:%.*]] = add i16 [[TMP8]], [[VAL_EXT]]
+; CHECK-NEXT:    [[GEP_PHI_TRANS_INSERT_1:%.*]] = getelementptr inbounds i8, ptr [[PTR]], i64 1010
+; CHECK-NEXT:    [[VAL_PRE_1:%.*]] = load i8, ptr [[GEP_PHI_TRANS_INSERT_1]], align 1
+; CHECK-NEXT:    [[VAL_EXT_1:%.*]] = zext i8 [[VAL_PRE_1]] to i16
+; CHECK-NEXT:    [[ACCUM_NEXT_1:%.*]] = add i16 [[ACCUM_NEXT]], [[VAL_EXT_1]]
+; CHECK-NEXT:    [[GEP_PHI_TRANS_INSERT_2:%.*]] = getelementptr inbounds i8, ptr [[PTR]], i64 1011
+; CHECK-NEXT:    [[VAL_PRE_2:%.*]] = load i8, ptr [[GEP_PHI_TRANS_INSERT_2]], align 1
+; CHECK-NEXT:    [[VAL_EXT_2:%.*]] = zext i8 [[VAL_PRE_2]] to i16
+; CHECK-NEXT:    [[ACCUM_NEXT_2:%.*]] = add i16 [[ACCUM_NEXT_1]], [[VAL_EXT_2]]
+; CHECK-NEXT:    [[GEP_PHI_TRANS_INSERT_3:%.*]] = getelementptr inbounds i8, ptr [[PTR]], i64 1012
+; CHECK-NEXT:    [[VAL_PRE_3:%.*]] = load i8, ptr [[GEP_PHI_TRANS_INSERT_3]], align 1
+; CHECK-NEXT:    [[VAL_EXT_3:%.*]] = zext i8 [[VAL_PRE_3]] to i16
+; CHECK-NEXT:    [[ACCUM_NEXT_3:%.*]] = add i16 [[ACCUM_NEXT_2]], [[VAL_EXT_3]]
+; CHECK-NEXT:    [[GEP_PHI_TRANS_INSERT_4:%.*]] = getelementptr inbounds i8, ptr [[PTR]], i64 1013
+; CHECK-NEXT:    [[VAL_PRE_4:%.*]] = load i8, ptr [[GEP_PHI_TRANS_INSERT_4]], align 1
+; CHECK-NEXT:    [[VAL_EXT_4:%.*]] = zext i8 [[VAL_PRE_4]] to i16
+; CHECK-NEXT:    [[ACCUM_NEXT_4:%.*]] = add i16 [[ACCUM_NEXT_3]], [[VAL_EXT_4]]
+; CHECK-NEXT:    [[GEP_PHI_TRANS_INSERT_5:%.*]] = getelementptr inbounds i8, ptr [[PTR]], i64 1014
+; CHECK-NEXT:    [[VAL_PRE_5:%.*]] = load i8, ptr [[GEP_PHI_TRANS_INSERT_5]], align 1
+; CHECK-NEXT:    [[VAL_EXT_5:%.*]] = zext i8 [[VAL_PRE_5]] to i16
+; CHECK-NEXT:    [[ACCUM_NEXT_5:%.*]] = add i16 [[ACCUM_NEXT_4]], [[VAL_EXT_5]]
+; CHECK-NEXT:    [[GEP_PHI_TRANS_INSERT_6:%.*]] = getelementptr inbounds i8, ptr [[PTR]], i64 1015
+; CHECK-NEXT:    [[VAL_PRE_6:%.*]] = load i8, ptr [[GEP_PHI_TRANS_INSERT_6]], align 1
+; CHECK-NEXT:    [[VAL_EXT_6:%.*]] = zext i8 [[VAL_PRE_6]] to i16
+; CHECK-NEXT:    [[ACCUM_NEXT_6:%.*]] = add i16 [[ACCUM_NEXT_5]], [[VAL_EXT_6]]
+; CHECK-NEXT:    [[GEP_PHI_TRANS_INSERT_7:%.*]] = getelementptr inbounds i8, ptr [[PTR]], i64 1016
+; CHECK-NEXT:    [[VAL_PRE_7:%.*]] = load i8, ptr [[GEP_PHI_TRANS_INSERT_7]], align 1
+; CHECK-NEXT:    [[VAL_EXT_7:%.*]] = zext i8 [[VAL_PRE_7]] to i16
+; CHECK-NEXT:    [[ACCUM_NEXT_7:%.*]] = add i16 [[ACCUM_NEXT_6]], [[VAL_EXT_7]]
+; CHECK-NEXT:    [[GEP_PHI_TRANS_INSERT_8:%.*]] = getelementptr inbounds i8, ptr [[PTR]], i64 1017
+; CHECK-NEXT:    [[VAL_PRE_8:%.*]] = load i8, ptr [[GEP_PHI_TRANS_INSERT_8]], align 1
+; CHECK-NEXT:    [[VAL_EXT_8:%.*]] = zext i8 [[VAL_PRE_8]] to i16
+; CHECK-NEXT:    [[ACCUM_NEXT_8:%.*]] = add i16 [[ACCUM_NEXT_7]], [[VAL_EXT_8]]
+; CHECK-NEXT:    [[GEP_PHI_TRANS_INSERT_9:%.*]] = getelementptr inbounds i8, ptr [[PTR]], i64 1018
+; CHECK-NEXT:    [[VAL_PRE_9:%.*]] = load i8, ptr [[GEP_PHI_TRANS_INSERT_9]], align 1
+; CHECK-NEXT:    [[VAL_EXT_9:%.*]] = zext i8 [[VAL_PRE_9]] to i16
+; CHECK-NEXT:    [[ACCUM_NEXT_9:%.*]] = add i16 [[ACCUM_NEXT_8]], [[VAL_EXT_9]]
+; CHECK-NEXT:    [[GEP_PHI_TRANS_INSERT_10:%.*]] = getelementptr inbounds i8, ptr [[PTR]], i64 1019
+; CHECK-NEXT:    [[VAL_PRE_10:%.*]] = load i8, ptr [[GEP_PHI_TRANS_INSERT_10]], align 1
+; CHECK-NEXT:    [[VAL_EXT_10:%.*]] = zext i8 [[VAL_PRE_10]] to i16
+; CHECK-NEXT:    [[ACCUM_NEXT_10:%.*]] = add i16 [[ACCUM_NEXT_9]], [[VAL_EXT_10]]
+; CHECK-NEXT:    [[GEP_PHI_TRANS_INSERT_11:%.*]] = getelementptr inbounds i8, ptr [[PTR]], i64 1020
+; CHECK-NEXT:    [[VAL_PRE_11:%.*]] = load i8, ptr [[GEP_PHI_TRANS_INSERT_11]], align 1
+; CHECK-NEXT:    [[VAL_EXT_11:%.*]] = zext i8 [[VAL_PRE_11]] to i16
+; CHECK-NEXT:    [[ACCUM_NEXT_11:%.*]] = add i16 [[ACCUM_NEXT_10]], [[VAL_EXT_11]]
+; CHECK-NEXT:    [[GEP_PHI_TRANS_INSERT_12:%.*]] = getelementptr inbounds i8, ptr [[PTR]], i64 1021
+; CHECK-NEXT:    [[VAL_PRE_12:%.*]] = load i8, ptr [[GEP_PHI_TRANS_INSERT_12]], align 1
+; CHECK-NEXT:    [[VAL_EXT_12:%.*]] = zext i8 [[VAL_PRE_12]] to i16
+; CHECK-NEXT:    [[ACCUM_NEXT_12:%.*]] = add i16 [[ACCUM_NEXT_11]], [[VAL_EXT_12]]
+; CHECK-NEXT:    [[GEP_PHI_TRANS_INSERT_13:%.*]] = getelementptr inbounds i8, ptr [[PTR]], i64 1022
+; CHECK-NEXT:    [[VAL_PRE_13:%.*]] = load i8, ptr [[GEP_PHI_TRANS_INSERT_13]], align 1
+; CHECK-NEXT:    [[VAL_EXT_13:%.*]] = zext i8 [[VAL_PRE_13]] to i16
+; CHECK-NEXT:    [[ACCUM_NEXT_13:%.*]] = add i16 [[ACCUM_NEXT_12]], [[VAL_EXT_13]]
+; CHECK-NEXT:    [[GEP_PHI_TRANS_INSERT_14:%.*]] = getelementptr inbounds i8, ptr [[PTR]], i64 1023
+; CHECK-NEXT:    [[VAL_PRE_14:%.*]] = load i8, ptr [[GEP_PHI_TRANS_INSERT_14]], align 1
+; CHECK-NEXT:    [[VAL_EXT_14:%.*]] = zext i8 [[VAL_PRE_14]] to i16
+; CHECK-NEXT:    [[ACCUM_NEXT_14:%.*]] = add i16 [[ACCUM_NEXT_13]], [[VAL_EXT_14]]
+; CHECK-NEXT:    ret i16 [[ACCUM_NEXT_14]]
+;
+entry:
+  %first = load i8, ptr %ptr
+  call void @use(i8 %first) readonly
+  br label %loop
+
+loop:
+  %accum = phi i16 [ 0, %entry ], [ %accum.next, %loop ]
+  %iv = phi i64 [ 0, %entry ], [ %iv.next, %loop ]
+  %gep = getelementptr inbounds i8, ptr %ptr, i64 %iv
+  %val = load i8, ptr %gep, align 1
+  %iv.next = add nuw i64 %iv, 1
+  %val.ext = zext i8 %val to i16
+  %accum.next = add i16 %accum, %val.ext
+  %exit.cond = icmp eq i64 %iv.next, 1024
+  br i1 %exit.cond, label %exit, label %loop
+
+exit:
+  %lcssa.phi = phi i16 [ %accum.next, %loop ]
+  ret i16 %lcssa.phi
+}