diff --git a/llvm/test/Transforms/LoopVectorize/12-12-11-if-conv.ll b/llvm/test/Transforms/LoopVectorize/12-12-11-if-conv.ll
index 279d4e82ccb85..ed181f725d87c 100644
--- a/llvm/test/Transforms/LoopVectorize/12-12-11-if-conv.ll
+++ b/llvm/test/Transforms/LoopVectorize/12-12-11-if-conv.ll
@@ -35,5 +35,5 @@ if.end:                                           ; preds = %for.body, %if.then
   br i1 %exitcond, label %for.end, label %for.body
 
 for.end:                                          ; preds = %if.end, %entry
-  ret i32 undef
+  ret i32 poison
 }
diff --git a/llvm/test/Transforms/LoopVectorize/2012-10-20-infloop.ll b/llvm/test/Transforms/LoopVectorize/2012-10-20-infloop.ll
index 2b5960eb91e50..8869ed03424b5 100644
--- a/llvm/test/Transforms/LoopVectorize/2012-10-20-infloop.ll
+++ b/llvm/test/Transforms/LoopVectorize/2012-10-20-infloop.ll
@@ -56,7 +56,7 @@ if.then46:                                        ; preds = %for.body40
   br label %for.inc50
 
 for.inc50:                                        ; preds = %if.then46, %for.body40
-  %k.1 = phi i32 [ undef, %for.body40 ], [ %inc47, %if.then46 ]
+  %k.1 = phi i32 [ poison, %for.body40 ], [ %inc47, %if.then46 ]
   %step.1 = phi i32 [ %step.0121, %for.body40 ], [ %inc47, %if.then46 ]
   %indvars.iv.next124 = add i64 %indvars.iv123, 1
   %lftr.wideiv = trunc i64 %indvars.iv.next124 to i32
diff --git a/llvm/test/Transforms/LoopVectorize/AArch64/pr33053.ll b/llvm/test/Transforms/LoopVectorize/AArch64/pr33053.ll
index 20b536499afa7..614a67c219ad2 100644
--- a/llvm/test/Transforms/LoopVectorize/AArch64/pr33053.ll
+++ b/llvm/test/Transforms/LoopVectorize/AArch64/pr33053.ll
@@ -21,8 +21,8 @@ for.body.lr.ph:                                   ; preds = %entry
 
 for.body:                                         ; preds = %for.body.lr.ph, %for.body
   %indvars.iv = phi i64 [ 0, %for.body.lr.ph ], [ %indvars.iv.next, %for.body ]
-  %d.043 = phi i16 [ undef, %for.body.lr.ph ], [ %.sink28, %for.body ]
-  %c.042 = phi i16 [ undef, %for.body.lr.ph ], [ %c.0., %for.body ]
+  %d.043 = phi i16 [ poison, %for.body.lr.ph ], [ %.sink28, %for.body ]
+  %c.042 = phi i16 [ poison, %for.body.lr.ph ], [ %c.0., %for.body ]
   %arrayidx = getelementptr inbounds i16, ptr %1, i64 %indvars.iv
   %4 = load i16, ptr %arrayidx, align 2, !tbaa !7
   %cmp2 = icmp sgt i16 %c.042, %4
@@ -34,8 +34,8 @@ for.body:                                         ; preds = %for.body.lr.ph, %fo
   br i1 %cmp, label %for.body, label %for.end
 
 for.end:                                          ; preds = %for.body, %entry
-  %c.0.lcssa = phi i16 [ undef, %entry ], [ %c.0., %for.body ]
-  %d.0.lcssa = phi i16 [ undef, %entry ], [ %.sink28, %for.body ]
+  %c.0.lcssa = phi i16 [ poison, %entry ], [ %c.0., %for.body ]
+  %d.0.lcssa = phi i16 [ poison, %entry ], [ %.sink28, %for.body ]
   %cmp26 = icmp sgt i16 %c.0.lcssa, %d.0.lcssa
   %conv27 = zext i1 %cmp26 to i32
   ret i32 %conv27
diff --git a/llvm/test/Transforms/LoopVectorize/AArch64/pr36032.ll b/llvm/test/Transforms/LoopVectorize/AArch64/pr36032.ll
index 44820e061211a..0728234dc0c70 100644
--- a/llvm/test/Transforms/LoopVectorize/AArch64/pr36032.ll
+++ b/llvm/test/Transforms/LoopVectorize/AArch64/pr36032.ll
@@ -18,7 +18,7 @@ define void @_Z1dv() local_unnamed_addr #0 {
 ; CHECK-NEXT:    br label [[FOR_COND:%.*]]
 ; CHECK:       for.cond:
 ; CHECK-NEXT:    [[F_0:%.*]] = phi i32 [ 0, [[ENTRY:%.*]] ], [ [[ADD5:%.*]], [[FOR_COND_CLEANUP:%.*]] ]
-; CHECK-NEXT:    [[G_0:%.*]] = phi i32 [ undef, [[ENTRY]] ], [ [[G_1_LCSSA:%.*]], [[FOR_COND_CLEANUP]] ]
+; CHECK-NEXT:    [[G_0:%.*]] = phi i32 [ poison, [[ENTRY]] ], [ [[G_1_LCSSA:%.*]], [[FOR_COND_CLEANUP]] ]
 ; CHECK-NEXT:    [[CMP12:%.*]] = icmp ult i32 [[G_0]], 4
 ; CHECK-NEXT:    [[CONV:%.*]] = and i32 [[F_0]], 65535
 ; CHECK-NEXT:    br i1 [[CMP12]], label [[FOR_BODY_LR_PH:%.*]], label [[FOR_COND_CLEANUP]]
@@ -50,7 +50,7 @@ entry:
 
 for.cond:                                         ; preds = %for.cond.cleanup, %entry
   %f.0 = phi i32 [ 0, %entry ], [ %add5, %for.cond.cleanup ]
-  %g.0 = phi i32 [ undef, %entry ], [ %g.1.lcssa, %for.cond.cleanup ]
+  %g.0 = phi i32 [ poison, %entry ], [ %g.1.lcssa, %for.cond.cleanup ]
   %cmp12 = icmp ult i32 %g.0, 4
   %conv = and i32 %f.0, 65535
   br i1 %cmp12, label %for.body.lr.ph, label %for.cond.cleanup
diff --git a/llvm/test/Transforms/LoopVectorize/AArch64/sve-interleaved-accesses.ll b/llvm/test/Transforms/LoopVectorize/AArch64/sve-interleaved-accesses.ll
index cde89763b26c3..e1103b49e4edf 100644
--- a/llvm/test/Transforms/LoopVectorize/AArch64/sve-interleaved-accesses.ll
+++ b/llvm/test/Transforms/LoopVectorize/AArch64/sve-interleaved-accesses.ll
@@ -728,8 +728,8 @@ define void @int_float_struct(ptr nocapture readonly %p) #0 {
 ; CHECK-NEXT:    br label [[VECTOR_BODY:%.*]]
 ; CHECK:       vector.body:
 ; CHECK-NEXT:    [[INDEX:%.*]] = phi i64 [ 0, [[VECTOR_PH]] ], [ [[INDEX_NEXT:%.*]], [[VECTOR_BODY]] ]
-; CHECK-NEXT:    [[VEC_PHI:%.*]] = phi <vscale x 4 x float> [ insertelement (<vscale x 4 x float> zeroinitializer, float undef, i32 0), [[VECTOR_PH]] ], [ [[TMP7:%.*]], [[VECTOR_BODY]] ]
-; CHECK-NEXT:    [[VEC_PHI1:%.*]] = phi <vscale x 4 x i32> [ insertelement (<vscale x 4 x i32> zeroinitializer, i32 undef, i32 0), [[VECTOR_PH]] ], [ [[TMP6:%.*]], [[VECTOR_BODY]] ]
+; CHECK-NEXT:    [[VEC_PHI:%.*]] = phi <vscale x 4 x float> [ insertelement (<vscale x 4 x float> zeroinitializer, float poison, i32 0), [[VECTOR_PH]] ], [ [[TMP7:%.*]], [[VECTOR_BODY]] ]
+; CHECK-NEXT:    [[VEC_PHI1:%.*]] = phi <vscale x 4 x i32> [ insertelement (<vscale x 4 x i32> zeroinitializer, i32 poison, i32 0), [[VECTOR_PH]] ], [ [[TMP6:%.*]], [[VECTOR_BODY]] ]
 ; CHECK-NEXT:    [[TMP2:%.*]] = getelementptr inbounds [[STRUCT_INTFLOAT:%.*]], ptr [[P:%.*]], i64 [[INDEX]]
 ; CHECK-NEXT:    [[WIDE_VEC:%.*]] = load <vscale x 8 x i32>, ptr [[TMP2]], align 4
 ; CHECK-NEXT:    [[STRIDED_VEC:%.*]] = call { <vscale x 4 x i32>, <vscale x 4 x i32> } @llvm.vector.deinterleave2.nxv8i32(<vscale x 8 x i32> [[WIDE_VEC]])
@@ -755,8 +755,8 @@ for.cond.cleanup:                                 ; preds = %for.body
 
 for.body:                                         ; preds = %for.body, %entry
   %indvars.iv = phi i64 [ 0, %entry ], [ %indvars.iv.next, %for.body ]
-  %SumB.014 = phi float [ undef, %entry ], [ %add3, %for.body ]
-  %SumA.013 = phi i32 [ undef, %entry ], [ %add, %for.body ]
+  %SumB.014 = phi float [ poison, %entry ], [ %add3, %for.body ]
+  %SumA.013 = phi i32 [ poison, %entry ], [ %add, %for.body ]
   %a = getelementptr inbounds %struct.IntFloat, ptr %p, i64 %indvars.iv, i32 0
   %load1 = load i32, ptr %a, align 4
   %add = add nsw i32 %load1, %SumA.013
diff --git a/llvm/test/Transforms/LoopVectorize/ARM/arm-ieee-vectorize.ll b/llvm/test/Transforms/LoopVectorize/ARM/arm-ieee-vectorize.ll
index 44a48a9c262f5..fb2d0deb2479d 100644
--- a/llvm/test/Transforms/LoopVectorize/ARM/arm-ieee-vectorize.ll
+++ b/llvm/test/Transforms/LoopVectorize/ARM/arm-ieee-vectorize.ll
@@ -92,7 +92,7 @@ for.body.preheader:                               ; preds = %entry
 
 for.body:                                         ; preds = %for.body.preheader, %for.body
   %i.07 = phi i32 [ %inc, %for.body ], [ 0, %for.body.preheader ]
-  %Red.06 = phi i32 [ %add, %for.body ], [ undef, %for.body.preheader ]
+  %Red.06 = phi i32 [ %add, %for.body ], [ poison, %for.body.preheader ]
   %arrayidx = getelementptr inbounds i32, ptr %a, i32 %i.07
   %0 = load i32, ptr %arrayidx, align 4
   %arrayidx1 = getelementptr inbounds i32, ptr %b, i32 %i.07
@@ -108,7 +108,7 @@ for.end.loopexit:                                 ; preds = %for.body
   br label %for.end
 
 for.end:                                          ; preds = %for.end.loopexit, %entry
-  %Red.0.lcssa = phi i32 [ undef, %entry ], [ %add.lcssa, %for.end.loopexit ]
+  %Red.0.lcssa = phi i32 [ poison, %entry ], [ %add.lcssa, %for.end.loopexit ]
   ret i32 %Red.0.lcssa
 }
 
@@ -129,7 +129,7 @@ for.body.preheader:                               ; preds = %entry
 
 for.body:                                         ; preds = %for.body.preheader, %for.body
   %i.07 = phi i32 [ %inc, %for.body ], [ 0, %for.body.preheader ]
-  %Red.06 = phi float [ %add, %for.body ], [ undef, %for.body.preheader ]
+  %Red.06 = phi float [ %add, %for.body ], [ poison, %for.body.preheader ]
   %arrayidx = getelementptr inbounds float, ptr %a, i32 %i.07
   %0 = load float, ptr %arrayidx, align 4
   %arrayidx1 = getelementptr inbounds float, ptr %b, i32 %i.07
@@ -145,7 +145,7 @@ for.end.loopexit:                                 ; preds = %for.body
   br label %for.end
 
 for.end:                                          ; preds = %for.end.loopexit, %entry
-  %Red.0.lcssa = phi float [ undef, %entry ], [ %add.lcssa, %for.end.loopexit ]
+  %Red.0.lcssa = phi float [ poison, %entry ], [ %add.lcssa, %for.end.loopexit ]
   ret float %Red.0.lcssa
 }
 
@@ -252,7 +252,7 @@ for.body.preheader:                               ; preds = %entry
 
 for.body:                                         ; preds = %for.body.preheader, %for.body
   %i.07 = phi i32 [ %inc, %for.body ], [ 0, %for.body.preheader ]
-  %Red.06 = phi i32 [ %add, %for.body ], [ undef, %for.body.preheader ]
+  %Red.06 = phi i32 [ %add, %for.body ], [ poison, %for.body.preheader ]
   %arrayidx = getelementptr inbounds i32, ptr %a, i32 %i.07
   %0 = load i32, ptr %arrayidx, align 4
   %arrayidx1 = getelementptr inbounds i32, ptr %b, i32 %i.07
@@ -268,7 +268,7 @@ for.end.loopexit:                                 ; preds = %for.body
   br label %for.end
 
 for.end:                                          ; preds = %for.end.loopexit, %entry
-  %Red.0.lcssa = phi i32 [ undef, %entry ], [ %add.lcssa, %for.end.loopexit ]
+  %Red.0.lcssa = phi i32 [ poison, %entry ], [ %add.lcssa, %for.end.loopexit ]
   ret i32 %Red.0.lcssa
 }
 
@@ -285,7 +285,7 @@ for.body.preheader:                               ; preds = %entry
 
 for.body:                                         ; preds = %for.body.preheader, %for.body
   %i.07 = phi i32 [ %inc, %for.body ], [ 0, %for.body.preheader ]
-  %Red.06 = phi float [ %add, %for.body ], [ undef, %for.body.preheader ]
+  %Red.06 = phi float [ %add, %for.body ], [ poison, %for.body.preheader ]
   %arrayidx = getelementptr inbounds float, ptr %a, i32 %i.07
   %0 = load float, ptr %arrayidx, align 4
   %arrayidx1 = getelementptr inbounds float, ptr %b, i32 %i.07
@@ -301,7 +301,7 @@ for.end.loopexit:                                 ; preds = %for.body
   br label %for.end
 
 for.end:                                          ; preds = %for.end.loopexit, %entry
-  %Red.0.lcssa = phi float [ undef, %entry ], [ %add.lcssa, %for.end.loopexit ]
+  %Red.0.lcssa = phi float [ poison, %entry ], [ %add.lcssa, %for.end.loopexit ]
   ret float %Red.0.lcssa
 }
 
diff --git a/llvm/test/Transforms/LoopVectorize/ARM/mve-known-trip-count.ll b/llvm/test/Transforms/LoopVectorize/ARM/mve-known-trip-count.ll
index fe3504bc4b679..1651704cab93e 100644
--- a/llvm/test/Transforms/LoopVectorize/ARM/mve-known-trip-count.ll
+++ b/llvm/test/Transforms/LoopVectorize/ARM/mve-known-trip-count.ll
@@ -249,7 +249,7 @@ define dso_local i32 @predicated_test(i32 noundef %0, ptr %glob) #0 {
   br label %7
 
 7:                                                ; preds = %5, %155
-  %8 = phi i32 [ %10, %155 ], [ undef, %5 ]
+  %8 = phi i32 [ %10, %155 ], [ poison, %5 ]
   %9 = phi i32 [ %156, %155 ], [ 0, %5 ]
   %10 = shl i32 %8, 4
   store i32 %10, ptr %6, align 4
diff --git a/llvm/test/Transforms/LoopVectorize/ARM/scalar-block-cost.ll b/llvm/test/Transforms/LoopVectorize/ARM/scalar-block-cost.ll
index 596e42e9f094d..9c7309fdb2c33 100644
--- a/llvm/test/Transforms/LoopVectorize/ARM/scalar-block-cost.ll
+++ b/llvm/test/Transforms/LoopVectorize/ARM/scalar-block-cost.ll
@@ -70,7 +70,7 @@ for.cond.cleanup.loopexit:                        ; preds = %if.end
   br label %for.cond.cleanup
 
 for.cond.cleanup:                                 ; preds = %for.cond.cleanup.loopexit, %entry
-  ret i32 undef
+  ret i32 poison
 
 for.body:                                         ; preds = %for.body.preheader, %if.end
   %i.032 = phi i32 [ %inc, %if.end ], [ %start, %for.body.preheader ]
diff --git a/llvm/test/Transforms/LoopVectorize/X86/avx1.ll b/llvm/test/Transforms/LoopVectorize/X86/avx1.ll
index 9e205863b8367..880d91a58a5da 100644
--- a/llvm/test/Transforms/LoopVectorize/X86/avx1.ll
+++ b/llvm/test/Transforms/LoopVectorize/X86/avx1.ll
@@ -23,7 +23,7 @@ define i32 @read_mod_write_single_ptr(ptr nocapture %a, i32 %n) nounwind uwtable
   br i1 %exitcond, label %._crit_edge, label %.lr.ph
 
 ._crit_edge:                                      ; preds = %.lr.ph, %0
-  ret i32 undef
+  ret i32 poison
 }
 
 
@@ -47,6 +47,6 @@ define i32 @read_mod_i64(ptr nocapture %a, i32 %n) nounwind uwtable ssp {
   br i1 %exitcond, label %._crit_edge, label %.lr.ph
 
 ._crit_edge:                                      ; preds = %.lr.ph, %0
-  ret i32 undef
+  ret i32 poison
 }
 
diff --git a/llvm/test/Transforms/LoopVectorize/X86/consecutive-ptr-cg-bug.ll b/llvm/test/Transforms/LoopVectorize/X86/consecutive-ptr-cg-bug.ll
index e6b74062ad765..54abf3a023039 100644
--- a/llvm/test/Transforms/LoopVectorize/X86/consecutive-ptr-cg-bug.ll
+++ b/llvm/test/Transforms/LoopVectorize/X86/consecutive-ptr-cg-bug.ll
@@ -57,8 +57,8 @@ define void @test_01(i1 %arg) {
   %8 = phi i32 [ %.ph2, %.outer ], [ %7, %6 ]
   %9 = add i32 %8, 2
   %10 = zext i32 %9 to i64
-  %11 = getelementptr inbounds i32, ptr addrspace(1) undef, i64 %10
-  %12 = ashr i32 undef, %4
+  %11 = getelementptr inbounds i32, ptr addrspace(1) poison, i64 %10
+  %12 = ashr i32 poison, %4
   store i32 %12, ptr addrspace(1) %11, align 4
   %13 = add i32 %7, 1
   %14 = icmp sgt i32 %13, 61
@@ -96,8 +96,8 @@ define void @test_02(i1 %arg) {
   %8 = phi i32 [ %.ph2, %.outer ], [ %7, %6 ]
   %9 = add i32 %8, 2
   %10 = zext i32 %9 to i64
-  %11 = getelementptr inbounds i32, ptr addrspace(1) undef, i64 %10
-  %12 = ashr i32 undef, %4
+  %11 = getelementptr inbounds i32, ptr addrspace(1) poison, i64 %10
+  %12 = ashr i32 poison, %4
   store i32 %12, ptr addrspace(1) %11, align 4
   %13 = add i32 %7, 1
   %14 = icmp sgt i32 %13, 610
diff --git a/llvm/test/Transforms/LoopVectorize/X86/conversion-cost.ll b/llvm/test/Transforms/LoopVectorize/X86/conversion-cost.ll
index 6d2cda48f90ca..7778d690bba4e 100644
--- a/llvm/test/Transforms/LoopVectorize/X86/conversion-cost.ll
+++ b/llvm/test/Transforms/LoopVectorize/X86/conversion-cost.ll
@@ -77,7 +77,7 @@ define i32 @conversion_cost1(i32 %n, ptr nocapture %A, ptr nocapture %B) nounwin
 ; CHECK:       ._crit_edge.loopexit:
 ; CHECK-NEXT:    br label [[DOT_CRIT_EDGE]]
 ; CHECK:       ._crit_edge:
-; CHECK-NEXT:    ret i32 undef
+; CHECK-NEXT:    ret i32 poison
 ;
   %1 = icmp sgt i32 %n, 3
   br i1 %1, label %.lr.ph, label %._crit_edge
@@ -93,7 +93,7 @@ define i32 @conversion_cost1(i32 %n, ptr nocapture %A, ptr nocapture %B) nounwin
   br i1 %exitcond, label %._crit_edge, label %.lr.ph
 
 ._crit_edge:                                      ; preds = %.lr.ph, %0
-  ret i32 undef
+  ret i32 poison
 }
 
 define i32 @conversion_cost2(i32 %n, ptr nocapture %A, ptr nocapture %B) nounwind uwtable ssp {
@@ -156,7 +156,7 @@ define i32 @conversion_cost2(i32 %n, ptr nocapture %A, ptr nocapture %B) nounwin
 ; CHECK:       ._crit_edge.loopexit:
 ; CHECK-NEXT:    br label [[DOT_CRIT_EDGE]]
 ; CHECK:       ._crit_edge:
-; CHECK-NEXT:    ret i32 undef
+; CHECK-NEXT:    ret i32 poison
 ;
   %1 = icmp sgt i32 %n, 9
   br i1 %1, label %.lr.ph, label %._crit_edge
@@ -173,5 +173,5 @@ define i32 @conversion_cost2(i32 %n, ptr nocapture %A, ptr nocapture %B) nounwin
   br i1 %exitcond, label %._crit_edge, label %.lr.ph
 
 ._crit_edge:                                      ; preds = %.lr.ph, %0
-  ret i32 undef
+  ret i32 poison
 }
diff --git a/llvm/test/Transforms/LoopVectorize/X86/cost-model-assert.ll b/llvm/test/Transforms/LoopVectorize/X86/cost-model-assert.ll
index 4cff8753ba9b1..826f6133b252c 100644
--- a/llvm/test/Transforms/LoopVectorize/X86/cost-model-assert.ll
+++ b/llvm/test/Transforms/LoopVectorize/X86/cost-model-assert.ll
@@ -26,14 +26,14 @@ define void @cff_index_load_offsets(i1 %cond, i8 %x, ptr %p) #0 {
 ; CHECK-NEXT:    [[CONV73:%.*]] = zext i8 [[TMP0]] to i32
 ; CHECK-NEXT:    [[SHL74:%.*]] = shl nuw nsw i32 [[CONV73]], 16
 ; CHECK-NEXT:    [[OR75:%.*]] = or i32 [[SHL74]], [[SHL71]]
-; CHECK-NEXT:    [[TMP1:%.*]] = load i8, ptr undef, align 1, !tbaa [[CHAR_TBAA1]]
-; CHECK-NEXT:    [[SHL78:%.*]] = shl nuw nsw i32 undef, 8
+; CHECK-NEXT:    [[TMP1:%.*]] = load i8, ptr poison, align 1, !tbaa [[CHAR_TBAA1]]
+; CHECK-NEXT:    [[SHL78:%.*]] = shl nuw nsw i32 poison, 8
 ; CHECK-NEXT:    [[OR79:%.*]] = or i32 [[OR75]], [[SHL78]]
 ; CHECK-NEXT:    [[CONV81:%.*]] = zext i8 [[TMP1]] to i32
 ; CHECK-NEXT:    [[OR83:%.*]] = or i32 [[OR79]], [[CONV81]]
-; CHECK-NEXT:    store i32 [[OR83]], ptr undef, align 4, !tbaa [[LONG_TBAA4:![0-9]+]]
+; CHECK-NEXT:    store i32 [[OR83]], ptr poison, align 4, !tbaa [[LONG_TBAA4:![0-9]+]]
 ; CHECK-NEXT:    [[ADD_PTR86]] = getelementptr inbounds i8, ptr [[P_359]], i64 4
-; CHECK-NEXT:    [[CMP66:%.*]] = icmp ult ptr [[ADD_PTR86]], undef
+; CHECK-NEXT:    [[CMP66:%.*]] = icmp ult ptr [[ADD_PTR86]], poison
 ; CHECK-NEXT:    br i1 [[CMP66]], label %[[FOR_BODY68]], label %[[SW_EPILOG:.*]]
 ; CHECK:       [[SW_EPILOG]]:
 ; CHECK-NEXT:    unreachable
@@ -54,14 +54,14 @@ for.body68:                                       ; preds = %for.body68, %if.the
   %conv73 = zext i8 %0 to i32
   %shl74 = shl nuw nsw i32 %conv73, 16
   %or75 = or i32 %shl74, %shl71
-  %1 = load i8, ptr undef, align 1, !tbaa !1
-  %shl78 = shl nuw nsw i32 undef, 8
+  %1 = load i8, ptr poison, align 1, !tbaa !1
+  %shl78 = shl nuw nsw i32 poison, 8
   %or79 = or i32 %or75, %shl78
   %conv81 = zext i8 %1 to i32
   %or83 = or i32 %or79, %conv81
-  store i32 %or83, ptr undef, align 4, !tbaa !4
+  store i32 %or83, ptr poison, align 4, !tbaa !4
   %add.ptr86 = getelementptr inbounds i8, ptr %p.359, i64 4
-  %cmp66 = icmp ult ptr %add.ptr86, undef
+  %cmp66 = icmp ult ptr %add.ptr86, poison
   br i1 %cmp66, label %for.body68, label %sw.epilog
 
 sw.epilog:                                        ; preds = %for.body68
diff --git a/llvm/test/Transforms/LoopVectorize/X86/fp80-widest-type.ll b/llvm/test/Transforms/LoopVectorize/X86/fp80-widest-type.ll
index 2ef9d4b40d9a5..b6c9cf60b5b9c 100644
--- a/llvm/test/Transforms/LoopVectorize/X86/fp80-widest-type.ll
+++ b/llvm/test/Transforms/LoopVectorize/X86/fp80-widest-type.ll
@@ -14,7 +14,7 @@ define x86_fp80 @test() {
 ; CHECK-NEXT:    br label [[FOR_BODY3_I_3:%.*]]
 ; CHECK:       for.body3.i.3:
 ; CHECK-NEXT:    [[N_ADDR_112_I_3:%.*]] = phi i64 [ [[DEC_I_3:%.*]], [[FOR_BODY3_I_3]] ], [ 24, [[FOO_EXIT:%.*]] ]
-; CHECK-NEXT:    [[X_ADDR_111_I_3:%.*]] = phi x86_fp80 [ [[MUL_I_3:%.*]], [[FOR_BODY3_I_3]] ], [ undef, [[FOO_EXIT]] ]
+; CHECK-NEXT:    [[X_ADDR_111_I_3:%.*]] = phi x86_fp80 [ [[MUL_I_3:%.*]], [[FOR_BODY3_I_3]] ], [ poison, [[FOO_EXIT]] ]
 ; CHECK-NEXT:    [[MUL_I_3]] = fmul x86_fp80 [[X_ADDR_111_I_3]], 0xK40008000000000000000
 ; CHECK-NEXT:    [[DEC_I_3]] = add nsw i64 [[N_ADDR_112_I_3]], -1
 ; CHECK-NEXT:    [[CMP2_I_3:%.*]] = icmp sgt i64 [[N_ADDR_112_I_3]], 1
@@ -28,7 +28,7 @@ foo.exit:
 
 for.body3.i.3:                                    ; preds = %for.body3.i.3, %foo.exit
   %n.addr.112.i.3 = phi i64 [ %dec.i.3, %for.body3.i.3 ], [ 24, %foo.exit ]
-  %x.addr.111.i.3 = phi x86_fp80 [ %mul.i.3, %for.body3.i.3 ], [ undef, %foo.exit ]
+  %x.addr.111.i.3 = phi x86_fp80 [ %mul.i.3, %for.body3.i.3 ], [ poison, %foo.exit ]
   %mul.i.3 = fmul x86_fp80 %x.addr.111.i.3, 0xK40008000000000000000
   %dec.i.3 = add nsw i64 %n.addr.112.i.3, -1
   %cmp2.i.3 = icmp sgt i64 %n.addr.112.i.3, 1
diff --git a/llvm/test/Transforms/LoopVectorize/X86/interleaved-accesses-large-gap.ll b/llvm/test/Transforms/LoopVectorize/X86/interleaved-accesses-large-gap.ll
index e75d469506376..73224e6844db8 100644
--- a/llvm/test/Transforms/LoopVectorize/X86/interleaved-accesses-large-gap.ll
+++ b/llvm/test/Transforms/LoopVectorize/X86/interleaved-accesses-large-gap.ll
@@ -57,7 +57,7 @@ entry:
 for.body:
   %iv = phi i64 [ 1, %entry ], [ %iv.next, %for.body ]
   %iv.next = add nsw i64 %iv, 1
-  %arrayidx = getelementptr inbounds [3 x i32], ptr undef, i64 0, i64 %iv.next
+  %arrayidx = getelementptr inbounds [3 x i32], ptr poison, i64 0, i64 %iv.next
   %G2 = getelementptr i32, ptr %arrayidx, i64 %iv.next
   %G9 = getelementptr i32, ptr %G2, i32 -2147483647
   store i32 0, ptr %G2
@@ -87,7 +87,7 @@ entry:
 for.body:
   %iv = phi i64 [ 1, %entry ], [ %iv.next, %for.body ]
   %iv.next = add nsw i64 %iv, 1
-  %arrayidx = getelementptr inbounds [3 x i32], ptr undef, i64 0, i64 %iv.next
+  %arrayidx = getelementptr inbounds [3 x i32], ptr poison, i64 0, i64 %iv.next
   %G2 = getelementptr i32, ptr %arrayidx, i64 %iv.next
   %G9 = getelementptr i32, ptr %G2, i32 -2147483648
   store i32 0, ptr %G2
diff --git a/llvm/test/Transforms/LoopVectorize/X86/pr39160.ll b/llvm/test/Transforms/LoopVectorize/X86/pr39160.ll
index 878d288b918e4..d640984683ec0 100644
--- a/llvm/test/Transforms/LoopVectorize/X86/pr39160.ll
+++ b/llvm/test/Transforms/LoopVectorize/X86/pr39160.ll
@@ -13,7 +13,7 @@ bb:
   br label %bb2
 
 bb2:                                              ; preds = %bb2, %bb
-  %tmp4 = icmp slt i32 undef, 0
+  %tmp4 = icmp slt i32 poison, 0
   br i1 %tmp4, label %bb2, label %bb5
 
 bb5:                                              ; preds = %bb2
@@ -23,8 +23,8 @@ bb18:                                             ; preds = %bb33
   ret void
 
 bb19:                                             ; preds = %bb36, %bb5
-  %tmp21 = phi i64 [ undef, %bb36 ], [ 2, %bb5 ]
-  %tmp22 = phi i32 [ %tmp65, %bb36 ], [ undef, %bb5 ]
+  %tmp21 = phi i64 [ poison, %bb36 ], [ 2, %bb5 ]
+  %tmp22 = phi i32 [ %tmp65, %bb36 ], [ poison, %bb5 ]
   br label %bb50
 
 bb33:                                             ; preds = %bb62
@@ -48,7 +48,7 @@ bb50:                                             ; preds = %bb50, %bb19
   %tmp54 = add i32 %tmp52, 12
   %tmp55 = add i32 %tmp52, 13
   %tmp56 = add nuw nsw i64 %tmp53, 1
-  %tmp58 = icmp ult i64 %tmp53, undef
+  %tmp58 = icmp ult i64 %tmp53, poison
   br i1 %tmp58, label %bb50, label %bb46
 
 bb59:                                             ; preds = %bb46
diff --git a/llvm/test/Transforms/LoopVectorize/X86/rauw-bug.ll b/llvm/test/Transforms/LoopVectorize/X86/rauw-bug.ll
index df1c4f979986c..31fabd3a1724a 100644
--- a/llvm/test/Transforms/LoopVectorize/X86/rauw-bug.ll
+++ b/llvm/test/Transforms/LoopVectorize/X86/rauw-bug.ll
@@ -21,10 +21,10 @@ while.cond63.preheader.while.end76_crit_edge:
   ret void
 
 while.body:
-  %d2_fx.015 = phi double [ %sub52, %while.body ], [ undef, %entry ]
-  %d2_fy.014 = phi double [ %sub58, %while.body ], [ undef, %entry ]
-  %d3_fy.013 = phi double [ %div56, %while.body ], [ undef, %entry ]
-  %d3_fx.012 = phi double [ %div50, %while.body ], [ undef, %entry ]
+  %d2_fx.015 = phi double [ %sub52, %while.body ], [ poison, %entry ]
+  %d2_fy.014 = phi double [ %sub58, %while.body ], [ poison, %entry ]
+  %d3_fy.013 = phi double [ %div56, %while.body ], [ poison, %entry ]
+  %d3_fx.012 = phi double [ %div50, %while.body ], [ poison, %entry ]
   %div50 = fmul double %d3_fx.012, 1.250000e-01
   %sub52 = fsub double 0.000000e+00, %div50
   %div56 = fmul double %d3_fy.013, 1.250000e-01
diff --git a/llvm/test/Transforms/LoopVectorize/X86/runtime-limit.ll b/llvm/test/Transforms/LoopVectorize/X86/runtime-limit.ll
index af5c921c29149..edacc5a310a30 100644
--- a/llvm/test/Transforms/LoopVectorize/X86/runtime-limit.ll
+++ b/llvm/test/Transforms/LoopVectorize/X86/runtime-limit.ll
@@ -40,7 +40,7 @@ for.body:                                         ; preds = %for.body, %entry
   br i1 %exitcond, label %for.end, label %for.body
 
 for.end:                                          ; preds = %for.body
-  ret i32 undef
+  ret i32 poison
 }
 
 ; We are vectorizing with 12 runtime checks.
@@ -85,5 +85,5 @@ for.body:                                         ; preds = %for.body, %entry
   br i1 %exitcond, label %for.end, label %for.body
 
 for.end:                                          ; preds = %for.body
-  ret i32 undef
+  ret i32 poison
 }
diff --git a/llvm/test/Transforms/LoopVectorize/X86/unroll-pm.ll b/llvm/test/Transforms/LoopVectorize/X86/unroll-pm.ll
index 8971dfe507240..687ea2aeeb4b5 100644
--- a/llvm/test/Transforms/LoopVectorize/X86/unroll-pm.ll
+++ b/llvm/test/Transforms/LoopVectorize/X86/unroll-pm.ll
@@ -27,5 +27,5 @@ define i32 @bar(ptr nocapture %A, i32 %n) nounwind uwtable ssp {
   br i1 %exitcond, label %._crit_edge, label %.lr.ph
 
 ._crit_edge:                                      ; preds = %.lr.ph, %0
-  ret i32 undef
+  ret i32 poison
 }
diff --git a/llvm/test/Transforms/LoopVectorize/X86/x86_fp80-interleaved-access.ll b/llvm/test/Transforms/LoopVectorize/X86/x86_fp80-interleaved-access.ll
index 368361fd760ec..c12884c738fdb 100644
--- a/llvm/test/Transforms/LoopVectorize/X86/x86_fp80-interleaved-access.ll
+++ b/llvm/test/Transforms/LoopVectorize/X86/x86_fp80-interleaved-access.ll
@@ -15,7 +15,7 @@ for.cond.cleanup:
 
 for.body:
   %i.09 = phi i16 [ 0, %entry ], [ %add3, %for.body ]
-  %res.08 = phi x86_fp80 [ undef, %entry ], [ %3, %for.body ]
+  %res.08 = phi x86_fp80 [ poison, %entry ], [ %3, %for.body ]
   %arrayidx = getelementptr inbounds x86_fp80, ptr %a, i16 %i.09
   %0 = load x86_fp80, ptr %arrayidx, align 1
   %add = or i16 %i.09, 1
diff --git a/llvm/test/Transforms/LoopVectorize/bsd_regex.ll b/llvm/test/Transforms/LoopVectorize/bsd_regex.ll
index f64255f29d335..4c30ba5d9e929 100644
--- a/llvm/test/Transforms/LoopVectorize/bsd_regex.ll
+++ b/llvm/test/Transforms/LoopVectorize/bsd_regex.ll
@@ -39,7 +39,7 @@ define i32 @foo(ptr nocapture %A) {
 ; CHECK:       middle.block:
 ; CHECK-NEXT:    br label [[FOR_BODY:%.*]]
 ; CHECK:       for.end:
-; CHECK-NEXT:    ret i32 undef
+; CHECK-NEXT:    ret i32 poison
 ;
 entry:
   br label %for.body
@@ -55,7 +55,7 @@ for.body:
   br i1 %exitcond, label %for.end, label %for.body
 
 for.end:
-  ret i32 undef
+  ret i32 poison
 }
 
 
diff --git a/llvm/test/Transforms/LoopVectorize/demanded-bits-of-pointer-instruction.ll b/llvm/test/Transforms/LoopVectorize/demanded-bits-of-pointer-instruction.ll
index 41756ffb64e6c..2ca62b64dd7ce 100644
--- a/llvm/test/Transforms/LoopVectorize/demanded-bits-of-pointer-instruction.ll
+++ b/llvm/test/Transforms/LoopVectorize/demanded-bits-of-pointer-instruction.ll
@@ -10,7 +10,7 @@ start:
 
 loop:
   %ptr2 = phi ptr [ %ptr3, %loop ], [ %ptr, %start ]
-  %x = sext i8 undef to i64
+  %x = sext i8 poison to i64
   %ptr3 = getelementptr inbounds i8, ptr %ptr2, i64 1
   %cmp = icmp ult ptr %ptr3, %ptr_end
   br i1 %cmp, label %loop, label %end
diff --git a/llvm/test/Transforms/LoopVectorize/i8-induction.ll b/llvm/test/Transforms/LoopVectorize/i8-induction.ll
index 220fd64e6a829..ce2eaa985e6bb 100644
--- a/llvm/test/Transforms/LoopVectorize/i8-induction.ll
+++ b/llvm/test/Transforms/LoopVectorize/i8-induction.ll
@@ -20,7 +20,7 @@ scalar.ph:
 
 for.body:
   %mul16 = phi i8 [ 0, %scalar.ph ], [ %mul, %for.body ]              ; <------- i8 induction var.
-  %c.015 = phi i8 [ undef, %scalar.ph ], [ %conv8, %for.body ]
+  %c.015 = phi i8 [ poison, %scalar.ph ], [ %conv8, %for.body ]
   %conv2 = sext i8 %c.015 to i32
   %tobool = icmp ne i8 %c.015, 0
   %.sink = select i1 %tobool, i8 %c.015, i8 %0
diff --git a/llvm/test/Transforms/LoopVectorize/if-conversion-nest.ll b/llvm/test/Transforms/LoopVectorize/if-conversion-nest.ll
index 1588d02eff3db..72d4519a943cb 100644
--- a/llvm/test/Transforms/LoopVectorize/if-conversion-nest.ll
+++ b/llvm/test/Transforms/LoopVectorize/if-conversion-nest.ll
@@ -73,7 +73,7 @@ define i32 @foo(ptr nocapture %A, ptr nocapture %B, i32 %n) {
 ; CHECK:       for.end.loopexit:
 ; CHECK-NEXT:    br label [[FOR_END]]
 ; CHECK:       for.end:
-; CHECK-NEXT:    ret i32 undef
+; CHECK-NEXT:    ret i32 poison
 ;
 entry:
   %cmp26 = icmp sgt i32 %n, 0
@@ -106,7 +106,7 @@ if.end14:
   br i1 %exitcond, label %for.end, label %for.body
 
 for.end:
-  ret i32 undef
+  ret i32 poison
 }
 
 ; As above but with multiple variables set per block.
@@ -188,7 +188,7 @@ define i32 @multi_variable_if_nest(ptr nocapture %A, ptr nocapture %B, i32 %n) {
 ; CHECK:       for.end.loopexit:
 ; CHECK-NEXT:    br label [[FOR_END]]
 ; CHECK:       for.end:
-; CHECK-NEXT:    ret i32 undef
+; CHECK-NEXT:    ret i32 poison
 ;
 entry:
   %cmp26 = icmp sgt i32 %n, 0
@@ -224,5 +224,5 @@ if.end14:
   br i1 %exitcond, label %for.end, label %for.body
 
 for.end:
-  ret i32 undef
+  ret i32 poison
 }
diff --git a/llvm/test/Transforms/LoopVectorize/if-conversion.ll b/llvm/test/Transforms/LoopVectorize/if-conversion.ll
index 8a7f4a386fda1..b0fa105fcae70 100644
--- a/llvm/test/Transforms/LoopVectorize/if-conversion.ll
+++ b/llvm/test/Transforms/LoopVectorize/if-conversion.ll
@@ -94,7 +94,7 @@ define i32 @function0(ptr nocapture %a, ptr nocapture %b, i32 %start, i32 %end)
 ; CHECK:       [[FOR_END_LOOPEXIT]]:
 ; CHECK-NEXT:    br label %[[FOR_END]]
 ; CHECK:       [[FOR_END]]:
-; CHECK-NEXT:    ret i32 undef
+; CHECK-NEXT:    ret i32 poison
 ;
 entry:
   %cmp16 = icmp slt i32 %start, %end
@@ -127,7 +127,7 @@ if.end:
   br i1 %cmp, label %for.body, label %for.end
 
 for.end:
-  ret i32 undef
+  ret i32 poison
 }
 
 
@@ -237,6 +237,8 @@ for.end:                                          ; preds = %for.inc, %entry
 ; Handle PHI with single incoming value having a full mask.
 ; PR34523
 
+; NOTE: Changing PHI inputs from undef to poison leads to change in
+; behaviour of the test. Left as undef for now.
 define void @PR34523() {
 ; CHECK-LABEL: define void @PR34523() {
 ; CHECK-NEXT:  [[BB1:.*:]]
diff --git a/llvm/test/Transforms/LoopVectorize/if-pred-stores.ll b/llvm/test/Transforms/LoopVectorize/if-pred-stores.ll
index f7376a0f8e205..47d8ddb009045 100644
--- a/llvm/test/Transforms/LoopVectorize/if-pred-stores.ll
+++ b/llvm/test/Transforms/LoopVectorize/if-pred-stores.ll
@@ -277,7 +277,7 @@ define void @bug18724(i1 %cond, ptr %ptr, i1 %cond.2, i64 %v.1, i32 %v.2) {
 ; UNROLL-NOSIMPLIFY-NEXT:    [[INEWCHUNKS_2_LCSSA:%.*]] = phi i32 [ [[INEWCHUNKS_2]], [[FOR_INC23]] ], [ [[BIN_RDX]], [[MIDDLE_BLOCK]] ]
 ; UNROLL-NOSIMPLIFY-NEXT:    br label [[FOR_INC26]]
 ; UNROLL-NOSIMPLIFY:       for.inc26:
-; UNROLL-NOSIMPLIFY-NEXT:    [[INEWCHUNKS_1_LCSSA:%.*]] = phi i32 [ undef, [[FOR_BODY9]] ], [ [[INEWCHUNKS_2_LCSSA]], [[FOR_INC26_LOOPEXIT]] ]
+; UNROLL-NOSIMPLIFY-NEXT:    [[INEWCHUNKS_1_LCSSA:%.*]] = phi i32 [ poison, [[FOR_BODY9]] ], [ [[INEWCHUNKS_2_LCSSA]], [[FOR_INC26_LOOPEXIT]] ]
 ; UNROLL-NOSIMPLIFY-NEXT:    unreachable
 ;
 ; VEC-LABEL: @bug18724(
@@ -376,7 +376,7 @@ for.inc23:
   br i1 %cmp13, label %for.body14, label %for.inc26
 
 for.inc26:
-  %iNewChunks.1.lcssa = phi i32 [ undef, %for.body9 ], [ %iNewChunks.2, %for.inc23 ]
+  %iNewChunks.1.lcssa = phi i32 [ poison, %for.body9 ], [ %iNewChunks.2, %for.inc23 ]
   unreachable
 }
 
@@ -391,8 +391,8 @@ define void @minimal_bit_widths(i1 %c) {
 ; UNROLL:       vector.body:
 ; UNROLL-NEXT:    [[INDEX:%.*]] = phi i64 [ 0, [[ENTRY:%.*]] ], [ [[INDEX_NEXT:%.*]], [[PRED_STORE_CONTINUE2:%.*]] ]
 ; UNROLL-NEXT:    [[TMP1:%.*]] = add i64 [[INDEX]], 1
-; UNROLL-NEXT:    [[TMP2:%.*]] = getelementptr i8, ptr undef, i64 [[INDEX]]
-; UNROLL-NEXT:    [[TMP3:%.*]] = getelementptr i8, ptr undef, i64 [[TMP1]]
+; UNROLL-NEXT:    [[TMP2:%.*]] = getelementptr i8, ptr poison, i64 [[INDEX]]
+; UNROLL-NEXT:    [[TMP3:%.*]] = getelementptr i8, ptr poison, i64 [[TMP1]]
 ; UNROLL-NEXT:    [[TMP4:%.*]] = load i8, ptr [[TMP2]], align 1
 ; UNROLL-NEXT:    [[TMP5:%.*]] = load i8, ptr [[TMP3]], align 1
 ; UNROLL-NEXT:    br i1 [[C:%.*]], label [[PRED_STORE_IF:%.*]], label [[PRED_STORE_CONTINUE2]]
@@ -415,8 +415,8 @@ define void @minimal_bit_widths(i1 %c) {
 ; UNROLL-NOSIMPLIFY:       vector.body:
 ; UNROLL-NOSIMPLIFY-NEXT:    [[INDEX:%.*]] = phi i64 [ 0, [[VECTOR_PH]] ], [ [[INDEX_NEXT:%.*]], [[PRED_STORE_CONTINUE2:%.*]] ]
 ; UNROLL-NOSIMPLIFY-NEXT:    [[TMP1:%.*]] = add i64 [[INDEX]], 1
-; UNROLL-NOSIMPLIFY-NEXT:    [[TMP2:%.*]] = getelementptr i8, ptr undef, i64 [[INDEX]]
-; UNROLL-NOSIMPLIFY-NEXT:    [[TMP3:%.*]] = getelementptr i8, ptr undef, i64 [[TMP1]]
+; UNROLL-NOSIMPLIFY-NEXT:    [[TMP2:%.*]] = getelementptr i8, ptr poison, i64 [[INDEX]]
+; UNROLL-NOSIMPLIFY-NEXT:    [[TMP3:%.*]] = getelementptr i8, ptr poison, i64 [[TMP1]]
 ; UNROLL-NOSIMPLIFY-NEXT:    [[TMP4:%.*]] = load i8, ptr [[TMP2]], align 1
 ; UNROLL-NOSIMPLIFY-NEXT:    [[TMP5:%.*]] = load i8, ptr [[TMP3]], align 1
 ; UNROLL-NOSIMPLIFY-NEXT:    br i1 [[C:%.*]], label [[PRED_STORE_IF:%.*]], label [[PRED_STORE_CONTINUE:%.*]]
@@ -442,16 +442,16 @@ define void @minimal_bit_widths(i1 %c) {
 ; VEC-NEXT:    br label [[VECTOR_BODY:%.*]]
 ; VEC:       vector.body:
 ; VEC-NEXT:    [[INDEX:%.*]] = phi i64 [ 0, [[ENTRY:%.*]] ], [ [[INDEX_NEXT:%.*]], [[PRED_STORE_CONTINUE2:%.*]] ]
-; VEC-NEXT:    [[TMP1:%.*]] = getelementptr i8, ptr undef, i64 [[INDEX]]
+; VEC-NEXT:    [[TMP1:%.*]] = getelementptr i8, ptr poison, i64 [[INDEX]]
 ; VEC-NEXT:    [[WIDE_LOAD:%.*]] = load <2 x i8>, ptr [[TMP1]], align 1
 ; VEC-NEXT:    br i1 [[C:%.*]], label [[PRED_STORE_IF:%.*]], label [[PRED_STORE_CONTINUE2]]
 ; VEC:       pred.store.if:
 ; VEC-NEXT:    [[TMP8:%.*]] = add i64 [[INDEX]], 0
-; VEC-NEXT:    [[TMP3:%.*]] = getelementptr i8, ptr undef, i64 [[TMP8]]
+; VEC-NEXT:    [[TMP3:%.*]] = getelementptr i8, ptr poison, i64 [[TMP8]]
 ; VEC-NEXT:    [[TMP4:%.*]] = extractelement <2 x i8> [[WIDE_LOAD]], i32 0
 ; VEC-NEXT:    store i8 [[TMP4]], ptr [[TMP3]], align 1
 ; VEC-NEXT:    [[TMP5:%.*]] = add i64 [[INDEX]], 1
-; VEC-NEXT:    [[TMP6:%.*]] = getelementptr i8, ptr undef, i64 [[TMP5]]
+; VEC-NEXT:    [[TMP6:%.*]] = getelementptr i8, ptr poison, i64 [[TMP5]]
 ; VEC-NEXT:    [[TMP7:%.*]] = extractelement <2 x i8> [[WIDE_LOAD]], i32 1
 ; VEC-NEXT:    store i8 [[TMP7]], ptr [[TMP6]], align 1
 ; VEC-NEXT:    br label [[PRED_STORE_CONTINUE2]]
@@ -468,7 +468,7 @@ entry:
 for.body:
   %tmp0 = phi i64 [ %tmp6, %for.inc ], [ 0, %entry ]
   %tmp1 = phi i64 [ %tmp7, %for.inc ], [ 1000, %entry ]
-  %tmp2 = getelementptr i8, ptr undef, i64 %tmp0
+  %tmp2 = getelementptr i8, ptr poison, i64 %tmp0
   %tmp3 = load i8, ptr %tmp2, align 1
   br i1 %c, label %if.then, label %for.inc
 
diff --git a/llvm/test/Transforms/LoopVectorize/incorrect-dom-info.ll b/llvm/test/Transforms/LoopVectorize/incorrect-dom-info.ll
index 9e750022d8c4c..cf2930ef956d9 100644
--- a/llvm/test/Transforms/LoopVectorize/incorrect-dom-info.ll
+++ b/llvm/test/Transforms/LoopVectorize/incorrect-dom-info.ll
@@ -53,12 +53,12 @@ thread-pre-split.loopexit:                        ; preds = %11, %.thread-pre-sp
   br i1 false, label %thread-pre-split._crit_edge, label %.lr.ph21
 
 .lr.ph21:                                         ; preds = %26, %thread-pre-split.loopexit, %thread-pre-split.preheader
-  %d.020 = phi ptr [ undef, %26 ], [ %d.1.lcssa, %thread-pre-split.loopexit ], [ undef, %thread-pre-split.preheader ]
-  %10 = phi i64 [ %28, %26 ], [ undef, %thread-pre-split.loopexit ], [ undef, %thread-pre-split.preheader ]
+  %d.020 = phi ptr [ poison, %26 ], [ %d.1.lcssa, %thread-pre-split.loopexit ], [ poison, %thread-pre-split.preheader ]
+  %10 = phi i64 [ %28, %26 ], [ poison, %thread-pre-split.loopexit ], [ poison, %thread-pre-split.preheader ]
   br i1 %arg, label %11, label %22
 
 ; <label>:11                                      ; preds = %.lr.ph21
-  %12 = getelementptr inbounds [0 x i8], ptr @PL_utf8skip, i64 0, i64 undef
+  %12 = getelementptr inbounds [0 x i8], ptr @PL_utf8skip, i64 0, i64 poison
   %13 = load i8, ptr %12, align 1
   %14 = zext i8 %13 to i64
   %15 = icmp ugt i64 %14, %10
diff --git a/llvm/test/Transforms/LoopVectorize/interleaved-accesses-uniform-load.ll b/llvm/test/Transforms/LoopVectorize/interleaved-accesses-uniform-load.ll
index 081dcd831a1be..de5131b977506 100644
--- a/llvm/test/Transforms/LoopVectorize/interleaved-accesses-uniform-load.ll
+++ b/llvm/test/Transforms/LoopVectorize/interleaved-accesses-uniform-load.ll
@@ -32,7 +32,7 @@ define dso_local void @test_dead_load(i32 %arg) {
 ; CHECK-LABEL: @test_dead_load(
 ; CHECK: vector.body:
 ; CHECK: %wide.vec = load <16 x i32>, ptr %3, align 8
-; CHECK: %strided.vec = shufflevector <16 x i32> %wide.vec, <16 x i32> undef, <4 x i32> <i32 0, i32 4, i32 8, i32 12>
+; CHECK: %strided.vec = shufflevector <16 x i32> %wide.vec, <16 x i32> poison, <4 x i32> <i32 0, i32 4, i32 8, i32 12>
 bb1:
   br label %bb2
 
diff --git a/llvm/test/Transforms/LoopVectorize/interleaved-accesses.ll b/llvm/test/Transforms/LoopVectorize/interleaved-accesses.ll
index b4cad1142134c..d5aaf11ee4f22 100644
--- a/llvm/test/Transforms/LoopVectorize/interleaved-accesses.ll
+++ b/llvm/test/Transforms/LoopVectorize/interleaved-accesses.ll
@@ -791,8 +791,8 @@ define void @int_float_struct(ptr nocapture readonly %A) #0 {
 ; CHECK-NEXT:    br label [[VECTOR_BODY:%.*]]
 ; CHECK:       vector.body:
 ; CHECK-NEXT:    [[INDEX:%.*]] = phi i64 [ 0, [[VECTOR_PH]] ], [ [[INDEX_NEXT:%.*]], [[VECTOR_BODY]] ]
-; CHECK-NEXT:    [[VEC_PHI:%.*]] = phi <4 x float> [ <float undef, float 0.000000e+00, float 0.000000e+00, float 0.000000e+00>, [[VECTOR_PH]] ], [ [[TMP3:%.*]], [[VECTOR_BODY]] ]
-; CHECK-NEXT:    [[VEC_PHI1:%.*]] = phi <4 x i32> [ <i32 undef, i32 0, i32 0, i32 0>, [[VECTOR_PH]] ], [ [[TMP2:%.*]], [[VECTOR_BODY]] ]
+; CHECK-NEXT:    [[VEC_PHI:%.*]] = phi <4 x float> [ <float poison, float 0.000000e+00, float 0.000000e+00, float 0.000000e+00>, [[VECTOR_PH]] ], [ [[TMP3:%.*]], [[VECTOR_BODY]] ]
+; CHECK-NEXT:    [[VEC_PHI1:%.*]] = phi <4 x i32> [ <i32 poison, i32 0, i32 0, i32 0>, [[VECTOR_PH]] ], [ [[TMP2:%.*]], [[VECTOR_BODY]] ]
 ; CHECK-NEXT:    [[TMP0:%.*]] = getelementptr inbounds [[STRUCT_INTFLOAT:%.*]], ptr [[A:%.*]], i64 [[INDEX]]
 ; CHECK-NEXT:    [[WIDE_VEC:%.*]] = load <8 x i32>, ptr [[TMP0]], align 4
 ; CHECK-NEXT:    [[STRIDED_VEC:%.*]] = shufflevector <8 x i32> [[WIDE_VEC]], <8 x i32> poison, <4 x i32> <i32 0, i32 2, i32 4, i32 6>
@@ -822,8 +822,8 @@ for.cond.cleanup:                                 ; preds = %for.body
 
 for.body:                                         ; preds = %for.body, %entry
   %indvars.iv = phi i64 [ 0, %entry ], [ %indvars.iv.next, %for.body ]
-  %SumB.014 = phi float [ undef, %entry ], [ %add3, %for.body ]
-  %SumA.013 = phi i32 [ undef, %entry ], [ %add, %for.body ]
+  %SumB.014 = phi float [ poison, %entry ], [ %add3, %for.body ]
+  %SumA.013 = phi i32 [ poison, %entry ], [ %add, %for.body ]
   %a = getelementptr inbounds %struct.IntFloat, ptr %A, i64 %indvars.iv, i32 0
   %tmp = load i32, ptr %a, align 4
   %add = add nsw i32 %tmp, %SumA.013
diff --git a/llvm/test/Transforms/LoopVectorize/invariant-store-vectorization.ll b/llvm/test/Transforms/LoopVectorize/invariant-store-vectorization.ll
index 742ee649db3a2..5c7aecd226162 100644
--- a/llvm/test/Transforms/LoopVectorize/invariant-store-vectorization.ll
+++ b/llvm/test/Transforms/LoopVectorize/invariant-store-vectorization.ll
@@ -429,7 +429,7 @@ define i32 @multiple_uniform_stores(ptr nocapture %var1, ptr nocapture readonly
 ; CHECK:       for.end10.loopexit:
 ; CHECK-NEXT:    br label [[FOR_END10]]
 ; CHECK:       for.end10:
-; CHECK-NEXT:    ret i32 undef
+; CHECK-NEXT:    ret i32 poison
 ;
 entry:
   %cmp20 = icmp eq i32 %itr, 0
@@ -469,7 +469,7 @@ for.inc8:                                         ; preds = %for.body3, %for.con
   br i1 %exitcond26, label %for.end10, label %for.cond1.preheader
 
 for.end10:                                        ; preds = %for.inc8, %entry
-  ret i32 undef
+  ret i32 poison
 }
 
 ; second uniform store to the same address is conditional.
@@ -520,7 +520,7 @@ define i32 @multiple_uniform_stores_conditional(ptr nocapture %var1, ptr nocaptu
 ; CHECK:       for.end10.loopexit:
 ; CHECK-NEXT:    br label [[FOR_END10]]
 ; CHECK:       for.end10:
-; CHECK-NEXT:    ret i32 undef
+; CHECK-NEXT:    ret i32 poison
 ;
 entry:
   %cmp20 = icmp eq i32 %itr, 0
@@ -567,7 +567,7 @@ for.inc8:                                         ; preds = %for.body3, %for.con
   br i1 %exitcond26, label %for.end10, label %for.cond1.preheader
 
 for.end10:                                        ; preds = %for.inc8, %entry
-  ret i32 undef
+  ret i32 poison
 }
 
 ; cannot vectorize loop with unsafe dependency between uniform load (%i10) and store
diff --git a/llvm/test/Transforms/LoopVectorize/iv_outside_user.ll b/llvm/test/Transforms/LoopVectorize/iv_outside_user.ll
index 86515ebe25637..cc62f49986bb1 100644
--- a/llvm/test/Transforms/LoopVectorize/iv_outside_user.ll
+++ b/llvm/test/Transforms/LoopVectorize/iv_outside_user.ll
@@ -156,7 +156,7 @@ define ptr @both(i32 %k)  {
 ; CHECK-LABEL: define ptr @both(
 ; CHECK-SAME: i32 [[K:%.*]]) {
 ; CHECK-NEXT:  [[ENTRY:.*]]:
-; CHECK-NEXT:    [[BASE:%.*]] = getelementptr inbounds i32, ptr undef, i64 1
+; CHECK-NEXT:    [[BASE:%.*]] = getelementptr inbounds i32, ptr poison, i64 1
 ; CHECK-NEXT:    [[TMP0:%.*]] = add i32 [[K]], -1
 ; CHECK-NEXT:    [[TMP1:%.*]] = zext i32 [[TMP0]] to i64
 ; CHECK-NEXT:    [[TMP2:%.*]] = add nuw nsw i64 [[TMP1]], 1
@@ -169,7 +169,7 @@ define ptr @both(i32 %k)  {
 ; CHECK-NEXT:    [[TMP3:%.*]] = mul i64 [[N_VEC]], 4
 ; CHECK-NEXT:    [[IND_END1:%.*]] = getelementptr i8, ptr [[BASE]], i64 [[TMP3]]
 ; CHECK-NEXT:    [[TMP4:%.*]] = mul i64 [[N_VEC]], 4
-; CHECK-NEXT:    [[IND_END2:%.*]] = getelementptr i8, ptr undef, i64 [[TMP4]]
+; CHECK-NEXT:    [[IND_END2:%.*]] = getelementptr i8, ptr poison, i64 [[TMP4]]
 ; CHECK-NEXT:    br label %[[VECTOR_BODY:.*]]
 ; CHECK:       [[VECTOR_BODY]]:
 ; CHECK-NEXT:    [[INDEX:%.*]] = phi i64 [ 0, %[[VECTOR_PH]] ], [ [[INDEX_NEXT:%.*]], %[[VECTOR_BODY]] ]
@@ -183,7 +183,7 @@ define ptr @both(i32 %k)  {
 ; CHECK:       [[SCALAR_PH]]:
 ; CHECK-NEXT:    [[BC_RESUME_VAL:%.*]] = phi i32 [ [[IND_END]], %[[MIDDLE_BLOCK]] ], [ 0, %[[ENTRY]] ]
 ; CHECK-NEXT:    [[BC_RESUME_VAL1:%.*]] = phi ptr [ [[IND_END1]], %[[MIDDLE_BLOCK]] ], [ [[BASE]], %[[ENTRY]] ]
-; CHECK-NEXT:    [[BC_RESUME_VAL2:%.*]] = phi ptr [ [[IND_END2]], %[[MIDDLE_BLOCK]] ], [ undef, %[[ENTRY]] ]
+; CHECK-NEXT:    [[BC_RESUME_VAL2:%.*]] = phi ptr [ [[IND_END2]], %[[MIDDLE_BLOCK]] ], [ poison, %[[ENTRY]] ]
 ; CHECK-NEXT:    br label %[[FOR_BODY:.*]]
 ; CHECK:       [[FOR_BODY]]:
 ; CHECK-NEXT:    [[INC_PHI:%.*]] = phi i32 [ [[BC_RESUME_VAL]], %[[SCALAR_PH]] ], [ [[INC:%.*]], %[[FOR_BODY]] ]
@@ -198,13 +198,13 @@ define ptr @both(i32 %k)  {
 ; CHECK-NEXT:    ret ptr [[INC_LAG1_LCSSA]]
 ;
 entry:
-  %base = getelementptr inbounds i32, ptr undef, i64 1
+  %base = getelementptr inbounds i32, ptr poison, i64 1
   br label %for.body
 
 for.body:
   %inc.phi = phi i32 [ 0, %entry ], [ %inc, %for.body ]
   %inc.lag1 = phi ptr [ %base, %entry ], [ %tmp, %for.body]
-  %inc.lag2 = phi ptr [ undef, %entry ], [ %inc.lag1, %for.body]
+  %inc.lag2 = phi ptr [ poison, %entry ], [ %inc.lag1, %for.body]
   %tmp = getelementptr inbounds i32, ptr %inc.lag1, i64 1
   %inc = add nsw i32 %inc.phi, 1
   %cmp = icmp eq i32 %inc, %k
@@ -269,8 +269,8 @@ define void @PR30742() {
 ; CHECK:       [[BB1_LOOPEXIT:.*]]:
 ; CHECK-NEXT:    br label %[[BB1]]
 ; CHECK:       [[BB1]]:
-; CHECK-NEXT:    [[TMP00:%.*]] = load i32, ptr undef, align 16
-; CHECK-NEXT:    [[TMP01:%.*]] = sub i32 [[TMP00]], undef
+; CHECK-NEXT:    [[TMP00:%.*]] = load i32, ptr poison, align 16
+; CHECK-NEXT:    [[TMP01:%.*]] = sub i32 [[TMP00]], poison
 ; CHECK-NEXT:    [[TMP02:%.*]] = icmp slt i32 [[TMP01]], 1
 ; CHECK-NEXT:    [[TMP03:%.*]] = select i1 [[TMP02]], i32 1, i32 [[TMP01]]
 ; CHECK-NEXT:    [[TMP04:%.*]] = add nsw i32 [[TMP03]], -7
@@ -307,7 +307,7 @@ define void @PR30742() {
 ; CHECK-NEXT:    br i1 [[TMP07]], label %[[BB2]], label %[[BB3]], {{!llvm.loop ![0-9]+}}
 ; CHECK:       [[BB3]]:
 ; CHECK-NEXT:    [[TMP08:%.*]] = phi i32 [ [[TMP05]], %[[BB2]] ], [ [[IND_ESCAPE]], %[[MIDDLE_BLOCK10]] ]
-; CHECK-NEXT:    [[TMP09:%.*]] = sub i32 [[TMP00]], undef
+; CHECK-NEXT:    [[TMP09:%.*]] = sub i32 [[TMP00]], poison
 ; CHECK-NEXT:    [[TMP10:%.*]] = icmp slt i32 [[TMP09]], 1
 ; CHECK-NEXT:    [[TMP11:%.*]] = select i1 [[TMP10]], i32 1, i32 [[TMP09]]
 ; CHECK-NEXT:    [[TMP12:%.*]] = add nsw i32 [[TMP11]], -7
@@ -346,8 +346,8 @@ BB0:
   br label %BB1
 
 BB1:
-  %tmp00 = load i32, ptr undef, align 16
-  %tmp01 = sub i32 %tmp00, undef
+  %tmp00 = load i32, ptr poison, align 16
+  %tmp01 = sub i32 %tmp00, poison
   %tmp02 = icmp slt i32 %tmp01, 1
   %tmp03 = select i1 %tmp02, i32 1, i32 %tmp01
   %tmp04 = add nsw i32 %tmp03, -7
@@ -361,7 +361,7 @@ BB2:
 
 BB3:
   %tmp08 = phi i32 [ %tmp05, %BB2 ]
-  %tmp09 = sub i32 %tmp00, undef
+  %tmp09 = sub i32 %tmp00, poison
   %tmp10 = icmp slt i32 %tmp09, 1
   %tmp11 = select i1 %tmp10, i32 1, i32 %tmp09
   %tmp11.inc = add nsw i32 %tmp11, -7
diff --git a/llvm/test/Transforms/LoopVectorize/lcssa-crashes.ll b/llvm/test/Transforms/LoopVectorize/lcssa-crashes.ll
index 6265336d1e45e..d43d5e4f9584a 100644
--- a/llvm/test/Transforms/LoopVectorize/lcssa-crashes.ll
+++ b/llvm/test/Transforms/LoopVectorize/lcssa-crashes.ll
@@ -3,6 +3,8 @@
 
 target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64-S128"
 
+; NOTE: Changing PHI inputs from undef to poison leads to change in
+; behaviour of the test. Left as undef for now.
 define void @test() {
 ; CHECK-LABEL: @test(
 ; CHECK-NEXT:    br label [[FOR_BODY_LR_PH_I_I_I:%.*]]
@@ -76,14 +78,14 @@ L1:
 define void @test3() {
 ; CHECK-LABEL: @test3(
 ; CHECK-NEXT:  entry:
-; CHECK-NEXT:    [[ADD41:%.*]] = add i32 undef, undef
+; CHECK-NEXT:    [[ADD41:%.*]] = add i32 poison, poison
 ; CHECK-NEXT:    [[IDXPROM4736:%.*]] = zext i32 [[ADD41]] to i64
 ; CHECK-NEXT:    br label [[WHILE_BODY:%.*]]
 ; CHECK:       while.body:
 ; CHECK-NEXT:    [[IDXPROM4738:%.*]] = phi i64 [ [[IDXPROM47:%.*]], [[WHILE_BODY]] ], [ [[IDXPROM4736]], [[ENTRY:%.*]] ]
 ; CHECK-NEXT:    [[POS_337:%.*]] = phi i32 [ [[INC46:%.*]], [[WHILE_BODY]] ], [ [[ADD41]], [[ENTRY]] ]
 ; CHECK-NEXT:    [[INC46]] = add i32 [[POS_337]], 1
-; CHECK-NEXT:    [[ARRAYIDX48:%.*]] = getelementptr inbounds [1024 x i8], ptr undef, i64 0, i64 [[IDXPROM4738]]
+; CHECK-NEXT:    [[ARRAYIDX48:%.*]] = getelementptr inbounds [1024 x i8], ptr poison, i64 0, i64 [[IDXPROM4738]]
 ; CHECK-NEXT:    store i8 0, ptr [[ARRAYIDX48]], align 1
 ; CHECK-NEXT:    [[AND43:%.*]] = and i32 [[INC46]], 3
 ; CHECK-NEXT:    [[CMP44:%.*]] = icmp eq i32 [[AND43]], 0
@@ -95,7 +97,7 @@ define void @test3() {
 ; CHECK-NEXT:    ret void
 ;
 entry:
-  %add41 = add i32 undef, undef
+  %add41 = add i32 poison, poison
   %idxprom4736 = zext i32 %add41 to i64
   br label %while.body
 
@@ -103,7 +105,7 @@ while.body:
   %idxprom4738 = phi i64 [ %idxprom47, %while.body ], [ %idxprom4736, %entry ]
   %pos.337 = phi i32 [ %inc46, %while.body ], [ %add41, %entry ]
   %inc46 = add i32 %pos.337, 1
-  %arrayidx48 = getelementptr inbounds [1024 x i8], ptr undef, i64 0, i64 %idxprom4738
+  %arrayidx48 = getelementptr inbounds [1024 x i8], ptr poison, i64 0, i64 %idxprom4738
   store i8 0, ptr %arrayidx48, align 1
   %and43 = and i32 %inc46, 3
   %cmp44 = icmp eq i32 %and43, 0
diff --git a/llvm/test/Transforms/LoopVectorize/memdep.ll b/llvm/test/Transforms/LoopVectorize/memdep.ll
index b891b4312f18d..66ccd7864b9a3 100644
--- a/llvm/test/Transforms/LoopVectorize/memdep.ll
+++ b/llvm/test/Transforms/LoopVectorize/memdep.ll
@@ -149,7 +149,7 @@ for.body:
   br i1 %exitcond, label %for.body, label %for.end
 
 for.end:
-  ret i32 undef
+  ret i32 poison
 }
 
 ; Don't vectorize true loop carried dependencies that are not a multiple of the
diff --git a/llvm/test/Transforms/LoopVectorize/middle-block-dbg.ll b/llvm/test/Transforms/LoopVectorize/middle-block-dbg.ll
index 741ca559343d1..f1c442d7cdeec 100644
--- a/llvm/test/Transforms/LoopVectorize/middle-block-dbg.ll
+++ b/llvm/test/Transforms/LoopVectorize/middle-block-dbg.ll
@@ -48,7 +48,7 @@ for.cond.cleanup.loopexit:
   br label %for.cond.cleanup, !dbg !33
 
 for.cond.cleanup:
-  %2 = phi i32 [ %.pre, %for.cond.cleanup.loopexit ], [ undef, %entry ], !dbg !33
+  %2 = phi i32 [ %.pre, %for.cond.cleanup.loopexit ], [ poison, %entry ], !dbg !33
   %sub = add nsw i32 %0, -5, !dbg !33
   %idxprom3 = sext i32 %sub to i64, !dbg !33
   %arrayidx4 = getelementptr inbounds i32, ptr %vla, i64 %idxprom3, !dbg !33
diff --git a/llvm/test/Transforms/LoopVectorize/multi-use-reduction-bug.ll b/llvm/test/Transforms/LoopVectorize/multi-use-reduction-bug.ll
index 659dc62e7ab58..596ad6e9642da 100644
--- a/llvm/test/Transforms/LoopVectorize/multi-use-reduction-bug.ll
+++ b/llvm/test/Transforms/LoopVectorize/multi-use-reduction-bug.ll
@@ -22,8 +22,8 @@ entry:
   br label %for.body
 
 for.body:
-  %inc107 = phi i32 [ undef, %entry ], [ %inc10, %for.body ]
-  %inc6 = phi i32 [ %nf.promoted, %entry ], [ undef, %for.body ]
+  %inc107 = phi i32 [ poison, %entry ], [ %inc10, %for.body ]
+  %inc6 = phi i32 [ %nf.promoted, %entry ], [ poison, %for.body ]
   %add55 = phi i32 [ %n.promoted, %entry ], [ %add5, %for.body ]
   %.neg2 = sub i32 0, %inc6
   %add.neg = add i32 0, %add55
diff --git a/llvm/test/Transforms/LoopVectorize/nsw-crash.ll b/llvm/test/Transforms/LoopVectorize/nsw-crash.ll
index 106054d989776..b67bba4f42209 100644
--- a/llvm/test/Transforms/LoopVectorize/nsw-crash.ll
+++ b/llvm/test/Transforms/LoopVectorize/nsw-crash.ll
@@ -11,10 +11,10 @@ while.body.lr.ph:
   br label %while.body
 
 while.body:
-  %it.sroa.0.091 = phi ptr [ undef, %while.body.lr.ph ], [ %incdec.ptr.i, %while.body ]
+  %it.sroa.0.091 = phi ptr [ poison, %while.body.lr.ph ], [ %incdec.ptr.i, %while.body ]
   %incdec.ptr.i = getelementptr inbounds i32, ptr %it.sroa.0.091, i64 1
-  %inc32 = add i32 undef, 1                                        ; <------------- Make sure we don't set NSW flags to the undef.
-  %cmp.i11 = icmp eq ptr %incdec.ptr.i, undef
+  %inc32 = add i32 poison, 1                                        ; <------------- Make sure we don't set NSW flags to the poison.
+  %cmp.i11 = icmp eq ptr %incdec.ptr.i, poison
   br i1 %cmp.i11, label %while.end, label %while.body
 
 while.end:
diff --git a/llvm/test/Transforms/LoopVectorize/optsize.ll b/llvm/test/Transforms/LoopVectorize/optsize.ll
index 9f82795e1f71c..e7b76f820eb67 100644
--- a/llvm/test/Transforms/LoopVectorize/optsize.ll
+++ b/llvm/test/Transforms/LoopVectorize/optsize.ll
@@ -259,7 +259,7 @@ define void @pr43371() optsize {
 ; CHECK:       [[VECTOR_BODY]]:
 ; CHECK-NEXT:    [[INDEX:%.*]] = phi i32 [ 0, %[[VECTOR_PH]] ], [ [[INDEX_NEXT:%.*]], %[[VECTOR_BODY]] ]
 ; CHECK-NEXT:    [[VEC_IND:%.*]] = phi <2 x i16> [ <i16 0, i16 1>, %[[VECTOR_PH]] ], [ [[VEC_IND_NEXT:%.*]], %[[VECTOR_BODY]] ]
-; CHECK-NEXT:    [[TMP0:%.*]] = add <2 x i16> undef, [[VEC_IND]]
+; CHECK-NEXT:    [[TMP0:%.*]] = add <2 x i16> poison, [[VEC_IND]]
 ; CHECK-NEXT:    [[TMP1:%.*]] = zext <2 x i16> [[TMP0]] to <2 x i32>
 ; CHECK-NEXT:    [[TMP2:%.*]] = extractelement <2 x i32> [[TMP1]], i32 0
 ; CHECK-NEXT:    [[TMP3:%.*]] = getelementptr [2592 x i16], ptr @cm_array, i32 0, i32 [[TMP2]]
@@ -285,7 +285,7 @@ define void @pr43371() optsize {
 ; PGSO:       [[VECTOR_BODY]]:
 ; PGSO-NEXT:    [[INDEX:%.*]] = phi i32 [ 0, %[[VECTOR_PH]] ], [ [[INDEX_NEXT:%.*]], %[[VECTOR_BODY]] ]
 ; PGSO-NEXT:    [[VEC_IND:%.*]] = phi <2 x i16> [ <i16 0, i16 1>, %[[VECTOR_PH]] ], [ [[VEC_IND_NEXT:%.*]], %[[VECTOR_BODY]] ]
-; PGSO-NEXT:    [[TMP0:%.*]] = add <2 x i16> undef, [[VEC_IND]]
+; PGSO-NEXT:    [[TMP0:%.*]] = add <2 x i16> poison, [[VEC_IND]]
 ; PGSO-NEXT:    [[TMP1:%.*]] = zext <2 x i16> [[TMP0]] to <2 x i32>
 ; PGSO-NEXT:    [[TMP2:%.*]] = extractelement <2 x i32> [[TMP1]], i32 0
 ; PGSO-NEXT:    [[TMP3:%.*]] = getelementptr [2592 x i16], ptr @cm_array, i32 0, i32 [[TMP2]]
@@ -311,7 +311,7 @@ define void @pr43371() optsize {
 ; NPGSO:       [[VECTOR_BODY]]:
 ; NPGSO-NEXT:    [[INDEX:%.*]] = phi i32 [ 0, %[[VECTOR_PH]] ], [ [[INDEX_NEXT:%.*]], %[[VECTOR_BODY]] ]
 ; NPGSO-NEXT:    [[VEC_IND:%.*]] = phi <2 x i16> [ <i16 0, i16 1>, %[[VECTOR_PH]] ], [ [[VEC_IND_NEXT:%.*]], %[[VECTOR_BODY]] ]
-; NPGSO-NEXT:    [[TMP0:%.*]] = add <2 x i16> undef, [[VEC_IND]]
+; NPGSO-NEXT:    [[TMP0:%.*]] = add <2 x i16> poison, [[VEC_IND]]
 ; NPGSO-NEXT:    [[TMP1:%.*]] = zext <2 x i16> [[TMP0]] to <2 x i32>
 ; NPGSO-NEXT:    [[TMP2:%.*]] = extractelement <2 x i32> [[TMP1]], i32 0
 ; NPGSO-NEXT:    [[TMP3:%.*]] = getelementptr [2592 x i16], ptr @cm_array, i32 0, i32 [[TMP2]]
@@ -340,7 +340,7 @@ for.cond.cleanup28:
 
 for.body29:
   %i24.0170 = phi i16 [ 0, %entry], [ %inc37, %for.body29]
-  %add33 = add i16 undef, %i24.0170
+  %add33 = add i16 poison, %i24.0170
   %idxprom34 = zext i16 %add33 to i32
   %arrayidx35 = getelementptr [2592 x i16], ptr @cm_array, i32 0, i32 %idxprom34
   store i16 0, ptr %arrayidx35, align 1
@@ -360,7 +360,7 @@ define void @pr43371_pgso() !prof !14 {
 ; CHECK:       [[VECTOR_BODY]]:
 ; CHECK-NEXT:    [[INDEX:%.*]] = phi i32 [ 0, %[[VECTOR_PH]] ], [ [[INDEX_NEXT:%.*]], %[[VECTOR_BODY]] ]
 ; CHECK-NEXT:    [[VEC_IND:%.*]] = phi <2 x i16> [ <i16 0, i16 1>, %[[VECTOR_PH]] ], [ [[VEC_IND_NEXT:%.*]], %[[VECTOR_BODY]] ]
-; CHECK-NEXT:    [[TMP0:%.*]] = add <2 x i16> undef, [[VEC_IND]]
+; CHECK-NEXT:    [[TMP0:%.*]] = add <2 x i16> poison, [[VEC_IND]]
 ; CHECK-NEXT:    [[TMP1:%.*]] = zext <2 x i16> [[TMP0]] to <2 x i32>
 ; CHECK-NEXT:    [[TMP2:%.*]] = extractelement <2 x i32> [[TMP1]], i32 0
 ; CHECK-NEXT:    [[TMP3:%.*]] = getelementptr [2592 x i16], ptr @cm_array, i32 0, i32 [[TMP2]]
@@ -386,7 +386,7 @@ define void @pr43371_pgso() !prof !14 {
 ; PGSO:       [[VECTOR_BODY]]:
 ; PGSO-NEXT:    [[INDEX:%.*]] = phi i32 [ 0, %[[VECTOR_PH]] ], [ [[INDEX_NEXT:%.*]], %[[VECTOR_BODY]] ]
 ; PGSO-NEXT:    [[VEC_IND:%.*]] = phi <2 x i16> [ <i16 0, i16 1>, %[[VECTOR_PH]] ], [ [[VEC_IND_NEXT:%.*]], %[[VECTOR_BODY]] ]
-; PGSO-NEXT:    [[TMP0:%.*]] = add <2 x i16> undef, [[VEC_IND]]
+; PGSO-NEXT:    [[TMP0:%.*]] = add <2 x i16> poison, [[VEC_IND]]
 ; PGSO-NEXT:    [[TMP1:%.*]] = zext <2 x i16> [[TMP0]] to <2 x i32>
 ; PGSO-NEXT:    [[TMP2:%.*]] = extractelement <2 x i32> [[TMP1]], i32 0
 ; PGSO-NEXT:    [[TMP3:%.*]] = getelementptr [2592 x i16], ptr @cm_array, i32 0, i32 [[TMP2]]
@@ -408,13 +408,13 @@ define void @pr43371_pgso() !prof !14 {
 ; NPGSO-NEXT:  [[ENTRY:.*:]]
 ; NPGSO-NEXT:    br label %[[VECTOR_SCEVCHECK:.*]]
 ; NPGSO:       [[VECTOR_SCEVCHECK]]:
-; NPGSO-NEXT:    br i1 undef, label %[[SCALAR_PH:.*]], label %[[VECTOR_PH:.*]]
+; NPGSO-NEXT:    br i1 poison, label %[[SCALAR_PH:.*]], label %[[VECTOR_PH:.*]]
 ; NPGSO:       [[VECTOR_PH]]:
 ; NPGSO-NEXT:    br label %[[VECTOR_BODY:.*]]
 ; NPGSO:       [[VECTOR_BODY]]:
 ; NPGSO-NEXT:    [[INDEX:%.*]] = phi i32 [ 0, %[[VECTOR_PH]] ], [ [[INDEX_NEXT:%.*]], %[[VECTOR_BODY]] ]
 ; NPGSO-NEXT:    [[OFFSET_IDX:%.*]] = trunc i32 [[INDEX]] to i16
-; NPGSO-NEXT:    [[TMP1:%.*]] = add i16 undef, [[OFFSET_IDX]]
+; NPGSO-NEXT:    [[TMP1:%.*]] = add i16 poison, [[OFFSET_IDX]]
 ; NPGSO-NEXT:    [[TMP2:%.*]] = zext i16 [[TMP1]] to i32
 ; NPGSO-NEXT:    [[TMP3:%.*]] = getelementptr [2592 x i16], ptr @cm_array, i32 0, i32 [[TMP2]]
 ; NPGSO-NEXT:    store <2 x i16> zeroinitializer, ptr [[TMP3]], align 1
@@ -429,7 +429,7 @@ define void @pr43371_pgso() !prof !14 {
 ; NPGSO-NEXT:    unreachable
 ; NPGSO:       [[FOR_BODY29]]:
 ; NPGSO-NEXT:    [[I24_0170:%.*]] = phi i16 [ 0, %[[SCALAR_PH]] ], [ [[INC37:%.*]], %[[FOR_BODY29]] ]
-; NPGSO-NEXT:    [[ADD33:%.*]] = add i16 undef, [[I24_0170]]
+; NPGSO-NEXT:    [[ADD33:%.*]] = add i16 poison, [[I24_0170]]
 ; NPGSO-NEXT:    [[IDXPROM34:%.*]] = zext i16 [[ADD33]] to i32
 ; NPGSO-NEXT:    [[ARRAYIDX35:%.*]] = getelementptr [2592 x i16], ptr @cm_array, i32 0, i32 [[IDXPROM34]]
 ; NPGSO-NEXT:    store i16 0, ptr [[ARRAYIDX35]], align 1
@@ -449,7 +449,7 @@ for.cond.cleanup28:
 
 for.body29:
   %i24.0170 = phi i16 [ 0, %entry], [ %inc37, %for.body29]
-  %add33 = add i16 undef, %i24.0170
+  %add33 = add i16 poison, %i24.0170
   %idxprom34 = zext i16 %add33 to i32
   %arrayidx35 = getelementptr [2592 x i16], ptr @cm_array, i32 0, i32 %idxprom34
   store i16 0, ptr %arrayidx35, align 1
diff --git a/llvm/test/Transforms/LoopVectorize/partial-lcssa.ll b/llvm/test/Transforms/LoopVectorize/partial-lcssa.ll
index d700d484c56bc..5cfdf3d3a342f 100644
--- a/llvm/test/Transforms/LoopVectorize/partial-lcssa.ll
+++ b/llvm/test/Transforms/LoopVectorize/partial-lcssa.ll
@@ -50,5 +50,5 @@ for.end.outer.loopexit:                           ; preds = %for.end.inner
   br label %for.end.outer
 
 for.end.outer:                                    ; preds = %for.end.outer.loopexit, %entry
-  ret i64 undef
+  ret i64 poison
 }
diff --git a/llvm/test/Transforms/LoopVectorize/pr28541.ll b/llvm/test/Transforms/LoopVectorize/pr28541.ll
index ad7f6e7b16b16..c5d9471a243d6 100644
--- a/llvm/test/Transforms/LoopVectorize/pr28541.ll
+++ b/llvm/test/Transforms/LoopVectorize/pr28541.ll
@@ -67,5 +67,5 @@ while.cond.while.end_crit_edge:                   ; preds = %while.cond
   br label %while.end
 
 while.end:                                        ; preds = %while.cond.while.end_crit_edge, %entry
-  ret i32 undef
+  ret i32 poison
 }
diff --git a/llvm/test/Transforms/LoopVectorize/pr32859.ll b/llvm/test/Transforms/LoopVectorize/pr32859.ll
index 2d30e0c9ad10f..9e2c83b512c15 100644
--- a/llvm/test/Transforms/LoopVectorize/pr32859.ll
+++ b/llvm/test/Transforms/LoopVectorize/pr32859.ll
@@ -16,7 +16,7 @@ entry:
 
 for.cond1.preheader.i:                            ; preds = %if.end.2.i, %entry
   %c.06.i = phi i32 [ 0, %entry ], [ %inc5.i, %if.end.2.i ]
-  %tobool.i = icmp ne i32 undef, 0
+  %tobool.i = icmp ne i32 poison, 0
   br label %if.end.2.i
 
 if.end.2.i:                                       ; preds = %for.cond1.preheader.i
diff --git a/llvm/test/Transforms/LoopVectorize/pr36311.ll b/llvm/test/Transforms/LoopVectorize/pr36311.ll
index f2dfecc341e6f..5dd9e39876cf0 100644
--- a/llvm/test/Transforms/LoopVectorize/pr36311.ll
+++ b/llvm/test/Transforms/LoopVectorize/pr36311.ll
@@ -26,9 +26,9 @@ for.cond80.loopexit:                              ; preds = %for.body89
 
 for.body89.lr.ph:                                 ; preds = %for.cond80.loopexit, %for.body51
   %i79.0179 = phi i32 [ %add90, %for.cond80.loopexit ], [ 0, %for.body51 ]
-  %next_index.4178 = phi i32 [ %inc94.lcssa, %for.cond80.loopexit ], [ undef, %for.body51 ]
+  %next_index.4178 = phi i32 [ %inc94.lcssa, %for.cond80.loopexit ], [ poison, %for.body51 ]
   %add90 = add nuw i32 %i79.0179, 1
-  %mul91 = mul i32 %add90, undef
+  %mul91 = mul i32 %add90, poison
   br label %for.body89
 
 for.body89:                                       ; preds = %for.body89, %for.body89.lr.ph
@@ -38,10 +38,10 @@ for.body89:                                       ; preds = %for.body89, %for.bo
   %add93 = add i32 %add92, %mul91
   %inc94 = add i32 %next_index.5174, 1
   %conv95 = zext i32 %next_index.5174 to i64
-  %arrayidx.i160 = getelementptr inbounds i32, ptr undef, i64 %conv95
+  %arrayidx.i160 = getelementptr inbounds i32, ptr poison, i64 %conv95
   store i32 %add93, ptr %arrayidx.i160, align 4
 ;, !tbaa !1
-  %cmp87 = icmp ult i32 %add92, undef
+  %cmp87 = icmp ult i32 %add92, poison
   br i1 %cmp87, label %for.body89, label %for.cond80.loopexit
 
 nrvo.skipdtor.loopexit:                           ; preds = %for.cond80.loopexit
diff --git a/llvm/test/Transforms/LoopVectorize/reduction-inloop.ll b/llvm/test/Transforms/LoopVectorize/reduction-inloop.ll
index ec7fde81b205b..bf87a2f7351cd 100644
--- a/llvm/test/Transforms/LoopVectorize/reduction-inloop.ll
+++ b/llvm/test/Transforms/LoopVectorize/reduction-inloop.ll
@@ -1947,7 +1947,7 @@ define i32 @predicated_not_dominates_reduction(ptr nocapture noundef readonly %h
 ; CHECK-NEXT:    br label %[[VECTOR_BODY:.*]]
 ; CHECK:       [[VECTOR_BODY]]:
 ; CHECK-NEXT:    [[INDEX:%.*]] = phi i32 [ 0, %[[VECTOR_PH]] ], [ [[INDEX_NEXT:%.*]], %[[VECTOR_BODY]] ]
-; CHECK-NEXT:    [[VEC_PHI:%.*]] = phi i32 [ undef, %[[VECTOR_PH]] ], [ [[TMP7:%.*]], %[[VECTOR_BODY]] ]
+; CHECK-NEXT:    [[VEC_PHI:%.*]] = phi i32 [ poison, %[[VECTOR_PH]] ], [ [[TMP7:%.*]], %[[VECTOR_BODY]] ]
 ; CHECK-NEXT:    [[TMP1:%.*]] = getelementptr inbounds i8, ptr [[H]], i32 [[INDEX]]
 ; CHECK-NEXT:    [[WIDE_LOAD:%.*]] = load <4 x i8>, ptr [[TMP1]], align 1
 ; CHECK-NEXT:    [[TMP9:%.*]] = icmp ne <4 x i8> [[WIDE_LOAD]], zeroinitializer
@@ -1966,7 +1966,7 @@ define i32 @predicated_not_dominates_reduction(ptr nocapture noundef readonly %h
 ; CHECK-NEXT:    br i1 [[CMP_N]], label %[[FOR_END7:.*]], label %[[SCALAR_PH]]
 ; CHECK:       [[SCALAR_PH]]:
 ; CHECK-NEXT:    [[BC_RESUME_VAL:%.*]] = phi i32 [ [[N_VEC]], %[[MIDDLE_BLOCK]] ], [ 0, %[[ENTRY]] ]
-; CHECK-NEXT:    [[BC_MERGE_RDX:%.*]] = phi i32 [ [[TMP7]], %[[MIDDLE_BLOCK]] ], [ undef, %[[ENTRY]] ]
+; CHECK-NEXT:    [[BC_MERGE_RDX:%.*]] = phi i32 [ [[TMP7]], %[[MIDDLE_BLOCK]] ], [ poison, %[[ENTRY]] ]
 ; CHECK-NEXT:    br label %[[FOR_BODY2:.*]]
 ; CHECK:       [[FOR_BODY2]]:
 ; CHECK-NEXT:    [[A_117:%.*]] = phi i32 [ [[INC6:%.*]], %[[FOR_INC5:.*]] ], [ [[BC_RESUME_VAL]], %[[SCALAR_PH]] ]
@@ -2002,7 +2002,7 @@ define i32 @predicated_not_dominates_reduction(ptr nocapture noundef readonly %h
 ; CHECK-INTERLEAVED-NEXT:    br label %[[VECTOR_BODY:.*]]
 ; CHECK-INTERLEAVED:       [[VECTOR_BODY]]:
 ; CHECK-INTERLEAVED-NEXT:    [[INDEX:%.*]] = phi i32 [ 0, %[[VECTOR_PH]] ], [ [[INDEX_NEXT:%.*]], %[[VECTOR_BODY]] ]
-; CHECK-INTERLEAVED-NEXT:    [[VEC_PHI:%.*]] = phi i32 [ undef, %[[VECTOR_PH]] ], [ [[TMP11:%.*]], %[[VECTOR_BODY]] ]
+; CHECK-INTERLEAVED-NEXT:    [[VEC_PHI:%.*]] = phi i32 [ poison, %[[VECTOR_PH]] ], [ [[TMP11:%.*]], %[[VECTOR_BODY]] ]
 ; CHECK-INTERLEAVED-NEXT:    [[VEC_PHI1:%.*]] = phi i32 [ 0, %[[VECTOR_PH]] ], [ [[TMP14:%.*]], %[[VECTOR_BODY]] ]
 ; CHECK-INTERLEAVED-NEXT:    [[TMP1:%.*]] = getelementptr inbounds i8, ptr [[H]], i32 [[INDEX]]
 ; CHECK-INTERLEAVED-NEXT:    [[TMP2:%.*]] = getelementptr inbounds i8, ptr [[TMP1]], i32 4
@@ -2033,7 +2033,7 @@ define i32 @predicated_not_dominates_reduction(ptr nocapture noundef readonly %h
 ; CHECK-INTERLEAVED-NEXT:    br i1 [[CMP_N]], label %[[FOR_END7:.*]], label %[[SCALAR_PH]]
 ; CHECK-INTERLEAVED:       [[SCALAR_PH]]:
 ; CHECK-INTERLEAVED-NEXT:    [[BC_RESUME_VAL:%.*]] = phi i32 [ [[N_VEC]], %[[MIDDLE_BLOCK]] ], [ 0, %[[ENTRY]] ]
-; CHECK-INTERLEAVED-NEXT:    [[BC_MERGE_RDX:%.*]] = phi i32 [ [[BIN_RDX]], %[[MIDDLE_BLOCK]] ], [ undef, %[[ENTRY]] ]
+; CHECK-INTERLEAVED-NEXT:    [[BC_MERGE_RDX:%.*]] = phi i32 [ [[BIN_RDX]], %[[MIDDLE_BLOCK]] ], [ poison, %[[ENTRY]] ]
 ; CHECK-INTERLEAVED-NEXT:    br label %[[FOR_BODY2:.*]]
 ; CHECK-INTERLEAVED:       [[FOR_BODY2]]:
 ; CHECK-INTERLEAVED-NEXT:    [[A_117:%.*]] = phi i32 [ [[INC6:%.*]], %[[FOR_INC5:.*]] ], [ [[BC_RESUME_VAL]], %[[SCALAR_PH]] ]
@@ -2063,7 +2063,7 @@ entry:
 
 for.body2:                                        ; preds = %entry, %for.inc5
   %a.117 = phi i32 [ %inc6, %for.inc5 ], [ 0, %entry ]
-  %g.016 = phi i32 [ %g.1, %for.inc5 ], [ undef, %entry ]
+  %g.016 = phi i32 [ %g.1, %for.inc5 ], [ poison, %entry ]
   %arrayidx = getelementptr inbounds i8, ptr %h, i32 %a.117
   %0 = load i8, ptr %arrayidx, align 1
   %tobool3.not = icmp eq i8 %0, 0
@@ -2100,7 +2100,7 @@ define i32 @predicated_not_dominates_reduction_twoadd(ptr nocapture noundef read
 ; CHECK-NEXT:    br label %[[VECTOR_BODY:.*]]
 ; CHECK:       [[VECTOR_BODY]]:
 ; CHECK-NEXT:    [[INDEX:%.*]] = phi i32 [ 0, %[[VECTOR_PH]] ], [ [[INDEX_NEXT:%.*]], %[[VECTOR_BODY]] ]
-; CHECK-NEXT:    [[VEC_PHI:%.*]] = phi i32 [ undef, %[[VECTOR_PH]] ], [ [[TMP11:%.*]], %[[VECTOR_BODY]] ]
+; CHECK-NEXT:    [[VEC_PHI:%.*]] = phi i32 [ poison, %[[VECTOR_PH]] ], [ [[TMP11:%.*]], %[[VECTOR_BODY]] ]
 ; CHECK-NEXT:    [[TMP1:%.*]] = getelementptr inbounds i8, ptr [[H]], i32 [[INDEX]]
 ; CHECK-NEXT:    [[WIDE_LOAD:%.*]] = load <4 x i8>, ptr [[TMP1]], align 1
 ; CHECK-NEXT:    [[TMP6:%.*]] = icmp ne <4 x i8> [[WIDE_LOAD]], zeroinitializer
@@ -2122,7 +2122,7 @@ define i32 @predicated_not_dominates_reduction_twoadd(ptr nocapture noundef read
 ; CHECK-NEXT:    br i1 [[CMP_N]], label %[[FOR_END7:.*]], label %[[SCALAR_PH]]
 ; CHECK:       [[SCALAR_PH]]:
 ; CHECK-NEXT:    [[BC_RESUME_VAL:%.*]] = phi i32 [ [[N_VEC]], %[[MIDDLE_BLOCK]] ], [ 0, %[[ENTRY]] ]
-; CHECK-NEXT:    [[BC_MERGE_RDX:%.*]] = phi i32 [ [[TMP11]], %[[MIDDLE_BLOCK]] ], [ undef, %[[ENTRY]] ]
+; CHECK-NEXT:    [[BC_MERGE_RDX:%.*]] = phi i32 [ [[TMP11]], %[[MIDDLE_BLOCK]] ], [ poison, %[[ENTRY]] ]
 ; CHECK-NEXT:    br label %[[FOR_BODY2:.*]]
 ; CHECK:       [[FOR_BODY2]]:
 ; CHECK-NEXT:    [[A_117:%.*]] = phi i32 [ [[INC6:%.*]], %[[FOR_INC5:.*]] ], [ [[BC_RESUME_VAL]], %[[SCALAR_PH]] ]
@@ -2159,7 +2159,7 @@ define i32 @predicated_not_dominates_reduction_twoadd(ptr nocapture noundef read
 ; CHECK-INTERLEAVED-NEXT:    br label %[[VECTOR_BODY:.*]]
 ; CHECK-INTERLEAVED:       [[VECTOR_BODY]]:
 ; CHECK-INTERLEAVED-NEXT:    [[INDEX:%.*]] = phi i32 [ 0, %[[VECTOR_PH]] ], [ [[INDEX_NEXT:%.*]], %[[VECTOR_BODY]] ]
-; CHECK-INTERLEAVED-NEXT:    [[VEC_PHI:%.*]] = phi i32 [ undef, %[[VECTOR_PH]] ], [ [[TMP17:%.*]], %[[VECTOR_BODY]] ]
+; CHECK-INTERLEAVED-NEXT:    [[VEC_PHI:%.*]] = phi i32 [ poison, %[[VECTOR_PH]] ], [ [[TMP17:%.*]], %[[VECTOR_BODY]] ]
 ; CHECK-INTERLEAVED-NEXT:    [[VEC_PHI1:%.*]] = phi i32 [ 0, %[[VECTOR_PH]] ], [ [[TMP20:%.*]], %[[VECTOR_BODY]] ]
 ; CHECK-INTERLEAVED-NEXT:    [[TMP1:%.*]] = getelementptr inbounds i8, ptr [[H]], i32 [[INDEX]]
 ; CHECK-INTERLEAVED-NEXT:    [[TMP2:%.*]] = getelementptr inbounds i8, ptr [[TMP1]], i32 4
@@ -2196,7 +2196,7 @@ define i32 @predicated_not_dominates_reduction_twoadd(ptr nocapture noundef read
 ; CHECK-INTERLEAVED-NEXT:    br i1 [[CMP_N]], label %[[FOR_END7:.*]], label %[[SCALAR_PH]]
 ; CHECK-INTERLEAVED:       [[SCALAR_PH]]:
 ; CHECK-INTERLEAVED-NEXT:    [[BC_RESUME_VAL:%.*]] = phi i32 [ [[N_VEC]], %[[MIDDLE_BLOCK]] ], [ 0, %[[ENTRY]] ]
-; CHECK-INTERLEAVED-NEXT:    [[BC_MERGE_RDX:%.*]] = phi i32 [ [[BIN_RDX]], %[[MIDDLE_BLOCK]] ], [ undef, %[[ENTRY]] ]
+; CHECK-INTERLEAVED-NEXT:    [[BC_MERGE_RDX:%.*]] = phi i32 [ [[BIN_RDX]], %[[MIDDLE_BLOCK]] ], [ poison, %[[ENTRY]] ]
 ; CHECK-INTERLEAVED-NEXT:    br label %[[FOR_BODY2:.*]]
 ; CHECK-INTERLEAVED:       [[FOR_BODY2]]:
 ; CHECK-INTERLEAVED-NEXT:    [[A_117:%.*]] = phi i32 [ [[INC6:%.*]], %[[FOR_INC5:.*]] ], [ [[BC_RESUME_VAL]], %[[SCALAR_PH]] ]
@@ -2227,7 +2227,7 @@ entry:
 
 for.body2:                                        ; preds = %entry, %for.inc5
   %a.117 = phi i32 [ %inc6, %for.inc5 ], [ 0, %entry ]
-  %g.016 = phi i32 [ %g.1, %for.inc5 ], [ undef, %entry ]
+  %g.016 = phi i32 [ %g.1, %for.inc5 ], [ poison, %entry ]
   %arrayidx = getelementptr inbounds i8, ptr %h, i32 %a.117
   %0 = load i8, ptr %arrayidx, align 1
   %tobool3.not = icmp eq i8 %0, 0
@@ -2263,7 +2263,7 @@ define i32 @predicated_or_dominates_reduction(ptr %b) {
 ; CHECK-NEXT:    br label %[[VECTOR_BODY:.*]]
 ; CHECK:       [[VECTOR_BODY]]:
 ; CHECK-NEXT:    [[INDEX:%.*]] = phi i32 [ 0, %[[VECTOR_PH]] ], [ [[INDEX_NEXT:%.*]], %[[PRED_LOAD_CONTINUE6:.*]] ]
-; CHECK-NEXT:    [[VEC_PHI:%.*]] = phi i32 [ undef, %[[VECTOR_PH]] ], [ [[TMP48:%.*]], %[[PRED_LOAD_CONTINUE6]] ]
+; CHECK-NEXT:    [[VEC_PHI:%.*]] = phi i32 [ poison, %[[VECTOR_PH]] ], [ [[TMP48:%.*]], %[[PRED_LOAD_CONTINUE6]] ]
 ; CHECK-NEXT:    [[TMP0:%.*]] = add i32 [[INDEX]], 0
 ; CHECK-NEXT:    [[TMP1:%.*]] = add i32 [[INDEX]], 1
 ; CHECK-NEXT:    [[TMP2:%.*]] = add i32 [[INDEX]], 2
@@ -2340,7 +2340,7 @@ define i32 @predicated_or_dominates_reduction(ptr %b) {
 ; CHECK-INTERLEAVED-NEXT:    br label %[[VECTOR_BODY:.*]]
 ; CHECK-INTERLEAVED:       [[VECTOR_BODY]]:
 ; CHECK-INTERLEAVED-NEXT:    [[INDEX:%.*]] = phi i32 [ 0, %[[VECTOR_PH]] ], [ [[INDEX_NEXT:%.*]], %[[PRED_LOAD_CONTINUE15:.*]] ]
-; CHECK-INTERLEAVED-NEXT:    [[VEC_PHI:%.*]] = phi i32 [ undef, %[[VECTOR_PH]] ], [ [[TMP94:%.*]], %[[PRED_LOAD_CONTINUE15]] ]
+; CHECK-INTERLEAVED-NEXT:    [[VEC_PHI:%.*]] = phi i32 [ poison, %[[VECTOR_PH]] ], [ [[TMP94:%.*]], %[[PRED_LOAD_CONTINUE15]] ]
 ; CHECK-INTERLEAVED-NEXT:    [[VEC_PHI1:%.*]] = phi i32 [ 0, %[[VECTOR_PH]] ], [ [[TMP98:%.*]], %[[PRED_LOAD_CONTINUE15]] ]
 ; CHECK-INTERLEAVED-NEXT:    [[TMP0:%.*]] = add i32 [[INDEX]], 0
 ; CHECK-INTERLEAVED-NEXT:    [[TMP1:%.*]] = add i32 [[INDEX]], 1
@@ -2480,7 +2480,7 @@ for.cond.cleanup:                                 ; preds = %for.inc
 
 for.body:                                         ; preds = %entry, %for.inc
   %g.09 = phi i32 [ 0, %entry ], [ %inc3, %for.inc ]
-  %a.08 = phi i32 [ undef, %entry ], [ %a.1, %for.inc ]
+  %a.08 = phi i32 [ poison, %entry ], [ %a.1, %for.inc ]
   %d = getelementptr inbounds [0 x %struct.e], ptr %b, i32 0, i32 %g.09, i32 1
   %0 = load i32, ptr %d, align 4
   %tobool.not = icmp eq i32 %0, 0
diff --git a/llvm/test/Transforms/LoopVectorize/reduction-ptr.ll b/llvm/test/Transforms/LoopVectorize/reduction-ptr.ll
index 0656cd2b2aa94..dc68fb7839d8e 100644
--- a/llvm/test/Transforms/LoopVectorize/reduction-ptr.ll
+++ b/llvm/test/Transforms/LoopVectorize/reduction-ptr.ll
@@ -15,7 +15,7 @@ define void @PR49215(ptr %p, ptr %q) {
 ; CHECK-NEXT:    [[CMP2:%.*]] = icmp ult ptr [[Q:%.*]], [[G]]
 ; CHECK-NEXT:    [[UMIN]] = select i1 [[CMP2]], ptr [[Q]], ptr [[G]]
 ; CHECK-NEXT:    [[IV_NEXT]] = add nuw nsw i64 [[IV]], 1
-; CHECK-NEXT:    [[EXITCOND:%.*]] = icmp eq i64 [[IV_NEXT]], undef
+; CHECK-NEXT:    [[EXITCOND:%.*]] = icmp eq i64 [[IV_NEXT]], poison
 ; CHECK-NEXT:    br i1 [[EXITCOND]], label [[LOOPEXIT:%.*]], label [[FOR_BODY]]
 ; CHECK:       loopexit:
 ; CHECK-NEXT:    [[UMIN_LCSSA:%.*]] = phi ptr [ [[UMIN]], [[FOR_BODY]] ]
@@ -31,7 +31,7 @@ for.body:
   %cmp2 = icmp ult ptr %q, %g
   %umin = select i1 %cmp2, ptr %q, ptr %g
   %iv.next = add nuw nsw i64 %iv, 1
-  %exitcond = icmp eq i64 %iv.next, undef
+  %exitcond = icmp eq i64 %iv.next, poison
   br i1 %exitcond, label %loopexit, label %for.body
 
 loopexit:
diff --git a/llvm/test/Transforms/LoopVectorize/reduction-small-size.ll b/llvm/test/Transforms/LoopVectorize/reduction-small-size.ll
index 13cc1b657d231..0bafe1029bcc7 100644
--- a/llvm/test/Transforms/LoopVectorize/reduction-small-size.ll
+++ b/llvm/test/Transforms/LoopVectorize/reduction-small-size.ll
@@ -38,7 +38,7 @@ define i8 @PR34687(i1 %c, i32 %x, i32 %n) {
 ; CHECK-NEXT:    [[R:%.*]] = phi i32 [ [[BC_MERGE_RDX]], [[SCALAR_PH]] ], [ [[R_NEXT:%.*]], [[IF_END]] ]
 ; CHECK-NEXT:    br i1 [[C:%.*]], label [[IF_THEN:%.*]], label [[IF_END]]
 ; CHECK:       if.then:
-; CHECK-NEXT:    [[T0:%.*]] = sdiv i32 undef, undef
+; CHECK-NEXT:    [[T0:%.*]] = sdiv i32 poison, poison
 ; CHECK-NEXT:    br label [[IF_END]]
 ; CHECK:       if.end:
 ; CHECK-NEXT:    [[T1:%.*]] = and i32 [[R]], 255
@@ -60,7 +60,7 @@ for.body:
   br i1 %c, label %if.then, label %if.end
 
 if.then:
-  %t0 = sdiv i32 undef, undef
+  %t0 = sdiv i32 poison, poison
   br label %if.end
 
 if.end:
diff --git a/llvm/test/Transforms/LoopVectorize/reverse_iter.ll b/llvm/test/Transforms/LoopVectorize/reverse_iter.ll
index 43e916b48265e..f4b9e5fe6a379 100644
--- a/llvm/test/Transforms/LoopVectorize/reverse_iter.ll
+++ b/llvm/test/Transforms/LoopVectorize/reverse_iter.ll
@@ -26,7 +26,7 @@ define i32 @foo(i32 %n, ptr nocapture %A) {
 
 ; <label>:3                                       ; preds = %.lr.ph, %3
   %indvars.iv = phi i64 [ %2, %.lr.ph ], [ %indvars.iv.next, %3 ]
-  %sum.01 = phi i32 [ undef, %.lr.ph ], [ %9, %3 ]
+  %sum.01 = phi i32 [ poison, %.lr.ph ], [ %9, %3 ]
   %4 = trunc i64 %indvars.iv to i32
   %5 = shl nsw i32 %4, 1
   %6 = sext i32 %5 to i64
@@ -39,7 +39,7 @@ define i32 @foo(i32 %n, ptr nocapture %A) {
   br i1 %11, label %3, label %._crit_edge
 
 ._crit_edge:                                      ; preds = %3, %0
-  %sum.0.lcssa = phi i32 [ undef, %0 ], [ %9, %3 ]
+  %sum.0.lcssa = phi i32 [ poison, %0 ], [ %9, %3 ]
   ret i32 %sum.0.lcssa
 }
 
diff --git a/llvm/test/Transforms/LoopVectorize/runtime-check.ll b/llvm/test/Transforms/LoopVectorize/runtime-check.ll
index f87be5a115044..b7ca218638784 100644
--- a/llvm/test/Transforms/LoopVectorize/runtime-check.ll
+++ b/llvm/test/Transforms/LoopVectorize/runtime-check.ll
@@ -58,7 +58,7 @@ define i32 @foo(ptr nocapture %a, ptr nocapture %b, i32 %n) nounwind uwtable ssp
 ; CHECK:       for.end.loopexit:
 ; CHECK-NEXT:    br label [[FOR_END]], !dbg [[DBG14:![0-9]+]]
 ; CHECK:       for.end:
-; CHECK-NEXT:    ret i32 undef, !dbg [[DBG14]]
+; CHECK-NEXT:    ret i32 poison, !dbg [[DBG14]]
 ;
 ; FORCED_OPTSIZE-LABEL: @foo(
 ; FORCED_OPTSIZE-NEXT:  entry:
@@ -80,7 +80,7 @@ define i32 @foo(ptr nocapture %a, ptr nocapture %b, i32 %n) nounwind uwtable ssp
 ; FORCED_OPTSIZE:       for.end.loopexit:
 ; FORCED_OPTSIZE-NEXT:    br label [[FOR_END]], !dbg [[DBG10:![0-9]+]]
 ; FORCED_OPTSIZE:       for.end:
-; FORCED_OPTSIZE-NEXT:    ret i32 undef, !dbg [[DBG10]]
+; FORCED_OPTSIZE-NEXT:    ret i32 poison, !dbg [[DBG10]]
 ;
 entry:
   %cmp6 = icmp sgt i32 %n, 0, !dbg !6
@@ -99,7 +99,7 @@ for.body:                                         ; preds = %entry, %for.body
   br i1 %exitcond, label %for.end, label %for.body, !dbg !7
 
 for.end:                                          ; preds = %for.body, %entry
-  ret i32 undef, !dbg !8
+  ret i32 poison, !dbg !8
 }
 
 ; Make sure that we try to vectorize loops with a runtime check if the
diff --git a/llvm/test/Transforms/LoopVectorize/runtime-drop-crash.ll b/llvm/test/Transforms/LoopVectorize/runtime-drop-crash.ll
index c76c2c0ef47a2..cd1c949e29eab 100644
--- a/llvm/test/Transforms/LoopVectorize/runtime-drop-crash.ll
+++ b/llvm/test/Transforms/LoopVectorize/runtime-drop-crash.ll
@@ -12,12 +12,12 @@ entry:
 
 loop:
   %tmp3 = phi i64 [ 0, %entry ], [ %tmp18, %loop ]
-  %tmp4 = getelementptr inbounds %struct.foo, ptr %ptr, i64 undef
+  %tmp4 = getelementptr inbounds %struct.foo, ptr %ptr, i64 poison
   store i64 0, ptr %tmp4, align 8
   %tmp8 = add i64 1, %tmp3
   %tmp10 = getelementptr inbounds %struct.foo, ptr %ptr, i64 %tmp8
   store i64 1, ptr %tmp10, align 8
-  %tmp14 = add i64 undef, %tmp3
+  %tmp14 = add i64 poison, %tmp3
   %tmp16 = getelementptr inbounds %struct.foo, ptr %ptr, i64 %tmp14
   store i64 2, ptr %tmp16, align 8
   %tmp18 = add nuw nsw i64 %tmp3, 4
diff --git a/llvm/test/Transforms/LoopVectorize/scalable-first-order-recurrence.ll b/llvm/test/Transforms/LoopVectorize/scalable-first-order-recurrence.ll
index 60da3368b664e..0f72778e2da1b 100644
--- a/llvm/test/Transforms/LoopVectorize/scalable-first-order-recurrence.ll
+++ b/llvm/test/Transforms/LoopVectorize/scalable-first-order-recurrence.ll
@@ -202,7 +202,7 @@ define i32 @recurrence_2(ptr nocapture readonly %a, i32 %n) {
 ; CHECK-VF4UF1:       [[VECTOR_BODY]]:
 ; CHECK-VF4UF1-NEXT:    [[INDEX:%.*]] = phi i64 [ 0, %[[VECTOR_PH]] ], [ [[INDEX_NEXT:%.*]], %[[VECTOR_BODY]] ]
 ; CHECK-VF4UF1-NEXT:    [[VECTOR_RECUR:%.*]] = phi <vscale x 4 x i32> [ [[VECTOR_RECUR_INIT]], %[[VECTOR_PH]] ], [ [[WIDE_LOAD:%.*]], %[[VECTOR_BODY]] ]
-; CHECK-VF4UF1-NEXT:    [[VEC_PHI:%.*]] = phi <vscale x 4 x i32> [ undef, %[[VECTOR_PH]] ], [ [[TMP17:%.*]], %[[VECTOR_BODY]] ]
+; CHECK-VF4UF1-NEXT:    [[VEC_PHI:%.*]] = phi <vscale x 4 x i32> [ poison, %[[VECTOR_PH]] ], [ [[TMP17:%.*]], %[[VECTOR_BODY]] ]
 ; CHECK-VF4UF1-NEXT:    [[TMP10:%.*]] = getelementptr inbounds i32, ptr [[A]], i64 [[INDEX]]
 ; CHECK-VF4UF1-NEXT:    [[WIDE_LOAD]] = load <vscale x 4 x i32>, ptr [[TMP10]], align 4
 ; CHECK-VF4UF1-NEXT:    [[TMP12:%.*]] = call <vscale x 4 x i32> @llvm.vector.splice.nxv4i32(<vscale x 4 x i32> [[VECTOR_RECUR]], <vscale x 4 x i32> [[WIDE_LOAD]], i32 -1)
@@ -225,13 +225,13 @@ define i32 @recurrence_2(ptr nocapture readonly %a, i32 %n) {
 ; CHECK-VF4UF1:       [[SCALAR_PH]]:
 ; CHECK-VF4UF1-NEXT:    [[SCALAR_RECUR_INIT:%.*]] = phi i32 [ [[VECTOR_RECUR_EXTRACT]], %[[MIDDLE_BLOCK]] ], [ [[DOTPRE]], %[[FOR_PREHEADER]] ]
 ; CHECK-VF4UF1-NEXT:    [[BC_RESUME_VAL:%.*]] = phi i64 [ [[N_VEC]], %[[MIDDLE_BLOCK]] ], [ 0, %[[FOR_PREHEADER]] ]
-; CHECK-VF4UF1-NEXT:    [[BC_MERGE_RDX:%.*]] = phi i32 [ [[TMP19]], %[[MIDDLE_BLOCK]] ], [ undef, %[[FOR_PREHEADER]] ]
+; CHECK-VF4UF1-NEXT:    [[BC_MERGE_RDX:%.*]] = phi i32 [ [[TMP19]], %[[MIDDLE_BLOCK]] ], [ poison, %[[FOR_PREHEADER]] ]
 ; CHECK-VF4UF1-NEXT:    br label %[[SCALAR_BODY:.*]]
 ; CHECK-VF4UF1:       [[FOR_COND_CLEANUP_LOOPEXIT]]:
 ; CHECK-VF4UF1-NEXT:    [[MINMAX_0_COND_LCSSA:%.*]] = phi i32 [ [[MINMAX_0_COND:%.*]], %[[SCALAR_BODY]] ], [ [[TMP19]], %[[MIDDLE_BLOCK]] ]
 ; CHECK-VF4UF1-NEXT:    br label %[[FOR_COND_CLEANUP]]
 ; CHECK-VF4UF1:       [[FOR_COND_CLEANUP]]:
-; CHECK-VF4UF1-NEXT:    [[MINMAX_0_LCSSA:%.*]] = phi i32 [ undef, %[[ENTRY]] ], [ [[MINMAX_0_COND_LCSSA]], %[[FOR_COND_CLEANUP_LOOPEXIT]] ]
+; CHECK-VF4UF1-NEXT:    [[MINMAX_0_LCSSA:%.*]] = phi i32 [ poison, %[[ENTRY]] ], [ [[MINMAX_0_COND_LCSSA]], %[[FOR_COND_CLEANUP_LOOPEXIT]] ]
 ; CHECK-VF4UF1-NEXT:    ret i32 [[MINMAX_0_LCSSA]]
 ; CHECK-VF4UF1:       [[SCALAR_BODY]]:
 ;
@@ -261,8 +261,8 @@ define i32 @recurrence_2(ptr nocapture readonly %a, i32 %n) {
 ; CHECK-VF4UF2:       [[VECTOR_BODY]]:
 ; CHECK-VF4UF2-NEXT:    [[INDEX:%.*]] = phi i64 [ 0, %[[VECTOR_PH]] ], [ [[INDEX_NEXT:%.*]], %[[VECTOR_BODY]] ]
 ; CHECK-VF4UF2-NEXT:    [[VECTOR_RECUR:%.*]] = phi <vscale x 4 x i32> [ [[VECTOR_RECUR_INIT]], %[[VECTOR_PH]] ], [ [[WIDE_LOAD2:%.*]], %[[VECTOR_BODY]] ]
-; CHECK-VF4UF2-NEXT:    [[VEC_PHI:%.*]] = phi <vscale x 4 x i32> [ undef, %[[VECTOR_PH]] ], [ [[TMP25:%.*]], %[[VECTOR_BODY]] ]
-; CHECK-VF4UF2-NEXT:    [[VEC_PHI1:%.*]] = phi <vscale x 4 x i32> [ undef, %[[VECTOR_PH]] ], [ [[TMP26:%.*]], %[[VECTOR_BODY]] ]
+; CHECK-VF4UF2-NEXT:    [[VEC_PHI:%.*]] = phi <vscale x 4 x i32> [ poison, %[[VECTOR_PH]] ], [ [[TMP25:%.*]], %[[VECTOR_BODY]] ]
+; CHECK-VF4UF2-NEXT:    [[VEC_PHI1:%.*]] = phi <vscale x 4 x i32> [ poison, %[[VECTOR_PH]] ], [ [[TMP26:%.*]], %[[VECTOR_BODY]] ]
 ; CHECK-VF4UF2-NEXT:    [[TMP10:%.*]] = getelementptr inbounds i32, ptr [[A]], i64 [[INDEX]]
 ; CHECK-VF4UF2-NEXT:    [[TMP12:%.*]] = call i64 @llvm.vscale.i64()
 ; CHECK-VF4UF2-NEXT:    [[TMP13:%.*]] = shl nuw i64 [[TMP12]], 2
@@ -296,13 +296,13 @@ define i32 @recurrence_2(ptr nocapture readonly %a, i32 %n) {
 ; CHECK-VF4UF2:       [[SCALAR_PH]]:
 ; CHECK-VF4UF2-NEXT:    [[SCALAR_RECUR_INIT:%.*]] = phi i32 [ [[VECTOR_RECUR_EXTRACT]], %[[MIDDLE_BLOCK]] ], [ [[DOTPRE]], %[[FOR_PREHEADER]] ]
 ; CHECK-VF4UF2-NEXT:    [[BC_RESUME_VAL:%.*]] = phi i64 [ [[N_VEC]], %[[MIDDLE_BLOCK]] ], [ 0, %[[FOR_PREHEADER]] ]
-; CHECK-VF4UF2-NEXT:    [[BC_MERGE_RDX:%.*]] = phi i32 [ [[TMP28]], %[[MIDDLE_BLOCK]] ], [ undef, %[[FOR_PREHEADER]] ]
+; CHECK-VF4UF2-NEXT:    [[BC_MERGE_RDX:%.*]] = phi i32 [ [[TMP28]], %[[MIDDLE_BLOCK]] ], [ poison, %[[FOR_PREHEADER]] ]
 ; CHECK-VF4UF2-NEXT:    br label %[[SCALAR_BODY:.*]]
 ; CHECK-VF4UF2:       [[FOR_COND_CLEANUP_LOOPEXIT]]:
 ; CHECK-VF4UF2-NEXT:    [[MINMAX_0_COND_LCSSA:%.*]] = phi i32 [ [[MINMAX_0_COND:%.*]], %[[SCALAR_BODY]] ], [ [[TMP28]], %[[MIDDLE_BLOCK]] ]
 ; CHECK-VF4UF2-NEXT:    br label %[[FOR_COND_CLEANUP]]
 ; CHECK-VF4UF2:       [[FOR_COND_CLEANUP]]:
-; CHECK-VF4UF2-NEXT:    [[MINMAX_0_LCSSA:%.*]] = phi i32 [ undef, %[[ENTRY]] ], [ [[MINMAX_0_COND_LCSSA]], %[[FOR_COND_CLEANUP_LOOPEXIT]] ]
+; CHECK-VF4UF2-NEXT:    [[MINMAX_0_LCSSA:%.*]] = phi i32 [ poison, %[[ENTRY]] ], [ [[MINMAX_0_COND_LCSSA]], %[[FOR_COND_CLEANUP_LOOPEXIT]] ]
 ; CHECK-VF4UF2-NEXT:    ret i32 [[MINMAX_0_LCSSA]]
 ; CHECK-VF4UF2:       [[SCALAR_BODY]]:
 ;
@@ -320,13 +320,13 @@ for.cond.cleanup.loopexit:
   br label %for.cond.cleanup
 
 for.cond.cleanup:
-  %minmax.0.lcssa = phi i32 [ undef, %entry ], [ %minmax.0.cond.lcssa, %for.cond.cleanup.loopexit ]
+  %minmax.0.lcssa = phi i32 [ poison, %entry ], [ %minmax.0.cond.lcssa, %for.cond.cleanup.loopexit ]
   ret i32 %minmax.0.lcssa
 
 scalar.body:
   %0 = phi i32 [ %.pre, %for.preheader ], [ %1, %scalar.body ]
   %indvars.iv = phi i64 [ 0, %for.preheader ], [ %indvars.iv.next, %scalar.body ]
-  %minmax.028 = phi i32 [ undef, %for.preheader ], [ %minmax.0.cond, %scalar.body ]
+  %minmax.028 = phi i32 [ poison, %for.preheader ], [ %minmax.0.cond, %scalar.body ]
   %arrayidx = getelementptr inbounds i32, ptr %a, i64 %indvars.iv
   %1 = load i32, ptr %arrayidx, align 4
   %sub3 = sub nsw i32 %1, %0
diff --git a/llvm/test/Transforms/LoopVectorize/scev-exitlim-crash.ll b/llvm/test/Transforms/LoopVectorize/scev-exitlim-crash.ll
index 58ad64df1cbe1..7cb1c4bf04d17 100644
--- a/llvm/test/Transforms/LoopVectorize/scev-exitlim-crash.ll
+++ b/llvm/test/Transforms/LoopVectorize/scev-exitlim-crash.ll
@@ -16,9 +16,9 @@ entry:
   br label %for.cond
 
 for.cond:                                         ; preds = %for.cond, %entry
-  %i.0 = phi i32 [ undef, %entry ], [ %inc, %for.cond ]
+  %i.0 = phi i32 [ poison, %entry ], [ %inc, %for.cond ]
   %cmp = icmp slt i32 %i.0, 0
-  %fsub = fsub double undef, undef
+  %fsub = fsub double poison, poison
   %fadd = fadd double %fsub, 1.000000e+00
   %call = tail call i32 @fn2(double %fadd) #2
   %inc = add nsw i32 %i.0, 1
@@ -36,7 +36,7 @@ for.cond7.preheader.lr.ph:                        ; preds = %for.cond4.preheader
 for.cond7.preheader:                              ; preds = %for.cond7.preheader.lr.ph, %for.inc23
   %y.017 = phi i32 [ 0, %for.cond7.preheader.lr.ph ], [ %inc24, %for.inc23 ]
   %i.116 = phi i32 [ 0, %for.cond7.preheader.lr.ph ], [ %i.2.lcssa, %for.inc23 ]
-  %n.015 = phi i32 [ undef, %for.cond7.preheader.lr.ph ], [ %inc25, %for.inc23 ]
+  %n.015 = phi i32 [ poison, %for.cond7.preheader.lr.ph ], [ %inc25, %for.inc23 ]
   %1 = load i32, ptr @b, align 4, !tbaa !5
   %tobool11 = icmp eq i32 %1, 0
   br i1 %tobool11, label %for.inc23, label %for.body8.lr.ph
diff --git a/llvm/test/Transforms/LoopVectorize/select-reduction-start-value-may-be-undef-or-poison.ll b/llvm/test/Transforms/LoopVectorize/select-reduction-start-value-may-be-undef-or-poison.ll
index f4d5a84fe67c8..cd9eb72089646 100644
--- a/llvm/test/Transforms/LoopVectorize/select-reduction-start-value-may-be-undef-or-poison.ll
+++ b/llvm/test/Transforms/LoopVectorize/select-reduction-start-value-may-be-undef-or-poison.ll
@@ -23,7 +23,7 @@ define i64 @pr62565_incoming_value_known_undef(i64 %a, ptr %src) {
 ; CHECK:       middle.block:
 ; CHECK-NEXT:    [[TMP4:%.*]] = call i1 @llvm.vector.reduce.or.v2i1(<2 x i1> [[TMP2]])
 ; CHECK-NEXT:    [[TMP5:%.*]] = freeze i1 [[TMP4]]
-; CHECK-NEXT:    [[RDX_SELECT:%.*]] = select i1 [[TMP5]], i64 [[A]], i64 undef
+; CHECK-NEXT:    [[RDX_SELECT:%.*]] = select i1 [[TMP5]], i64 [[A]], i64 poison
 ; CHECK-NEXT:    br label [[EXIT:%.*]]
 ; CHECK:       exit:
 ; CHECK-NEXT:    ret i64 [[RDX_SELECT]]
@@ -33,7 +33,7 @@ entry:
 
 loop:
   %iv = phi i32 [ 1, %entry ], [ %add, %loop ]
-  %red = phi i64 [ undef, %entry ], [ %select, %loop ]
+  %red = phi i64 [ poison, %entry ], [ %select, %loop ]
   %gep = getelementptr inbounds i32, ptr %src, i32 %iv
   %l = load i32, ptr %gep
   %c = icmp eq i32 %l, 1
diff --git a/llvm/test/Transforms/LoopVectorize/undef-inst-bug.ll b/llvm/test/Transforms/LoopVectorize/undef-inst-bug.ll
index 1fccf546f4a67..a8fb73b167e5d 100644
--- a/llvm/test/Transforms/LoopVectorize/undef-inst-bug.ll
+++ b/llvm/test/Transforms/LoopVectorize/undef-inst-bug.ll
@@ -22,13 +22,13 @@ for.body:
   %indvars.iv17 = phi i64 [ %indvars.next, %for.body ], [ 128, %entry ]
 
   ; Loop invariant anchored in loop.
-  %idxprom21 = zext i32 undef to i64
+  %idxprom21 = zext i32 poison to i64
 
-  %arrayidx23 = getelementptr inbounds [100 x [100 x i32]], ptr undef, i64 0, i64 %idxprom21, i64 %indvars.iv17
-  store i32 undef, ptr %arrayidx23, align 4
+  %arrayidx23 = getelementptr inbounds [100 x [100 x i32]], ptr poison, i64 0, i64 %idxprom21, i64 %indvars.iv17
+  store i32 poison, ptr %arrayidx23, align 4
   %indvars.next= add i64 %indvars.iv17, -1
   %0 = trunc i64 %indvars.next to i32
-  %cmp15 = icmp ugt i32 %0, undef
+  %cmp15 = icmp ugt i32 %0, poison
   br i1 %cmp15, label %for.body, label %loopexit
 
 loopexit:
diff --git a/llvm/test/Transforms/LoopVectorize/uniform-blend.ll b/llvm/test/Transforms/LoopVectorize/uniform-blend.ll
index 985a9a2c2d155..7db53bcc8b474 100644
--- a/llvm/test/Transforms/LoopVectorize/uniform-blend.ll
+++ b/llvm/test/Transforms/LoopVectorize/uniform-blend.ll
@@ -102,7 +102,7 @@ define void @blend_chain_iv(i1 %c) {
 ; CHECK:       [[VECTOR_BODY]]:
 ; CHECK-NEXT:    [[INDEX:%.*]] = phi i64 [ 0, %[[VECTOR_PH]] ], [ [[INDEX_NEXT:%.*]], %[[VECTOR_BODY]] ]
 ; CHECK-NEXT:    [[PREDPHI1:%.*]] = phi <4 x i64> [ <i64 0, i64 1, i64 2, i64 3>, %[[VECTOR_PH]] ], [ [[VEC_IND_NEXT:%.*]], %[[VECTOR_BODY]] ]
-; CHECK-NEXT:    [[PREDPHI2:%.*]] = select <4 x i1> [[BROADCAST_SPLAT]], <4 x i64> [[PREDPHI1]], <4 x i64> undef
+; CHECK-NEXT:    [[PREDPHI2:%.*]] = select <4 x i1> [[BROADCAST_SPLAT]], <4 x i64> [[PREDPHI1]], <4 x i64> poison
 ; CHECK-NEXT:    [[TMP1:%.*]] = extractelement <4 x i64> [[PREDPHI2]], i32 0
 ; CHECK-NEXT:    [[TMP2:%.*]] = getelementptr inbounds [32 x i16], ptr @dst, i16 0, i64 [[TMP1]]
 ; CHECK-NEXT:    [[TMP3:%.*]] = extractelement <4 x i64> [[PREDPHI2]], i32 1
@@ -139,11 +139,11 @@ loop.next.2:
   br label %loop.next.3
 
 loop.next.3:
-  %blend.1 = phi i64 [ undef, %loop.next ], [ %iv, %loop.next.2 ]
+  %blend.1 = phi i64 [ poison, %loop.next ], [ %iv, %loop.next.2 ]
   br label %loop.latch
 
 loop.latch:                                       ; preds = %loop.next, %loop.header
-  %blend = phi i64 [ undef, %loop.header ], [ %blend.1, %loop.next.3 ]
+  %blend = phi i64 [ poison, %loop.header ], [ %blend.1, %loop.next.3 ]
   %dst.ptr = getelementptr inbounds [32 x i16], ptr @dst, i16 0, i64 %blend
   store i16 0, ptr %dst.ptr
   %iv.next = add nuw nsw i64 %iv, 1
diff --git a/llvm/test/Transforms/LoopVectorize/value-ptr-bug.ll b/llvm/test/Transforms/LoopVectorize/value-ptr-bug.ll
index 6579e0e33b308..ca07e94acb7e5 100644
--- a/llvm/test/Transforms/LoopVectorize/value-ptr-bug.ll
+++ b/llvm/test/Transforms/LoopVectorize/value-ptr-bug.ll
@@ -5,12 +5,12 @@ target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f3
 ; PR16073
 
 ; Because we were caching value pointers across a function call that could RAUW
-; we would generate an undefined value store below:
+; we would generate an poison value store below:
 ; SCEVExpander::expandCodeFor would change a value (the start value of an
 ; induction) that we cached in the induction variable list.
 
 ; CHECK-LABEL: @test_vh(
-; CHECK-NOT: store <4 x i8> undef
+; CHECK-NOT: store <4 x i8> poison
 
 define void @test_vh(ptr %ptr265, ptr %ptr266, i32 %sub267) {
 entry:
diff --git a/llvm/test/Transforms/LoopVectorize/vector-to-scalar-cast.ll b/llvm/test/Transforms/LoopVectorize/vector-to-scalar-cast.ll
index a6dcd4d1cfc11..333461e16bb14 100644
--- a/llvm/test/Transforms/LoopVectorize/vector-to-scalar-cast.ll
+++ b/llvm/test/Transforms/LoopVectorize/vector-to-scalar-cast.ll
@@ -7,7 +7,7 @@ define void @vector_to_scalar_cast(ptr %out) {
 ; CHECK-LABEL: define void @vector_to_scalar_cast(
 ; CHECK-SAME: ptr [[OUT:%.*]]) {
 ; CHECK-NEXT:  [[ENTRY:.*]]:
-; CHECK-NEXT:    [[VEC0:%.*]] = insertelement <2 x i16> undef, i16 0, i64 0
+; CHECK-NEXT:    [[VEC0:%.*]] = insertelement <2 x i16> poison, i16 0, i64 0
 ; CHECK-NEXT:    [[VEC1:%.*]] = insertelement <2 x i16> [[VEC0]], i16 0, i64 1
 ; CHECK-NEXT:    br label %[[LOOP:.*]]
 ; CHECK:       [[LOOP]]:
@@ -22,7 +22,7 @@ define void @vector_to_scalar_cast(ptr %out) {
 ; CHECK-NEXT:    ret void
 ;
 entry:
-  %vec0 = insertelement <2 x i16> undef, i16 0, i64 0
+  %vec0 = insertelement <2 x i16> poison, i16 0, i64 0
   %vec1 = insertelement <2 x i16> %vec0, i16 0, i64 1
   br label %loop
 
diff --git a/llvm/test/Transforms/LoopVectorize/write-only.ll b/llvm/test/Transforms/LoopVectorize/write-only.ll
index cc21b94bc3070..c763df7c5e612 100644
--- a/llvm/test/Transforms/LoopVectorize/write-only.ll
+++ b/llvm/test/Transforms/LoopVectorize/write-only.ll
@@ -21,7 +21,7 @@ define i32 @read_mod_write_single_ptr(ptr nocapture %a, i32 %n) nounwind uwtable
   br i1 %exitcond, label %._crit_edge, label %.lr.ph
 
 ._crit_edge:                                      ; preds = %.lr.ph, %0
-  ret i32 undef
+  ret i32 poison
 }
 
 ; Ensure that volatile stores are not vectorized.
@@ -44,5 +44,5 @@ define i32 @read_mod_write_single_ptr_volatile_store(ptr nocapture %a, i32 %n) n
   br i1 %exitcond, label %._crit_edge, label %.lr.ph
 
 ._crit_edge:                                      ; preds = %.lr.ph, %0
-  ret i32 undef
+  ret i32 poison
 }