diff --git a/llvm/lib/Analysis/ConstantFolding.cpp b/llvm/lib/Analysis/ConstantFolding.cpp
index 73cf336f5eb0..1df724a044bd 100644
--- a/llvm/lib/Analysis/ConstantFolding.cpp
+++ b/llvm/lib/Analysis/ConstantFolding.cpp
@@ -224,8 +224,19 @@ Constant *FoldBitCast(Constant *C, Type *DestTy, const DataLayout &DL) {
 
   // Loop over each source value, expanding into multiple results.
   for (unsigned i = 0; i != NumSrcElt; ++i) {
-    auto *Src = dyn_cast_or_null<ConstantInt>(C->getAggregateElement(i));
-    if (!Src)  // Reject constantexpr elements.
+    auto *Element = C->getAggregateElement(i);
+
+    if (!Element) // Reject constantexpr elements.
+      return ConstantExpr::getBitCast(C, DestTy);
+
+    if (isa<UndefValue>(Element)) {
+      // Correctly Propagate undef values.
+      Result.append(Ratio, UndefValue::get(DstEltTy));
+      continue;
+    }
+
+    auto *Src = dyn_cast<ConstantInt>(Element);
+    if (!Src)
       return ConstantExpr::getBitCast(C, DestTy);
 
     unsigned ShiftAmt = isLittleEndian ? 0 : DstBitSize*(Ratio-1);
diff --git a/llvm/test/Transforms/InstCombine/x86-sse4a.ll b/llvm/test/Transforms/InstCombine/x86-sse4a.ll
index d2714e0c6303..e36a73532259 100644
--- a/llvm/test/Transforms/InstCombine/x86-sse4a.ll
+++ b/llvm/test/Transforms/InstCombine/x86-sse4a.ll
@@ -57,8 +57,7 @@ define <2 x i64> @test_extrq_constant_undef(<2 x i64> %x, <16 x i8> %y) {
 
 define <2 x i64> @test_extrq_call_constexpr(<2 x i64> %x) {
 ; CHECK-LABEL: @test_extrq_call_constexpr(
-; CHECK-NEXT:    [[TMP1:%.*]] = call <2 x i64> @llvm.x86.sse4a.extrq(<2 x i64> %x, <16 x i8> bitcast (<2 x i64> <i64 0, i64 undef> to <16 x i8>))
-; CHECK-NEXT:    ret <2 x i64> [[TMP1]]
+; CHECK-NEXT:    ret <2 x i64> %x
 ;
   %1 = call <2 x i64> @llvm.x86.sse4a.extrq(<2 x i64> %x, <16 x i8> bitcast (<2 x i64> <i64 0, i64 undef> to <16 x i8>))
   ret <2 x i64> %1
@@ -133,7 +132,7 @@ define <2 x i64> @test_extrqi_constant_undef(<2 x i64> %x) {
 
 define <2 x i64> @test_extrqi_call_constexpr() {
 ; CHECK-LABEL: @test_extrqi_call_constexpr(
-; CHECK-NEXT:    ret <2 x i64> bitcast (<16 x i8> <i8 extractelement (<16 x i8> trunc (<16 x i16> bitcast (<4 x i64> <i64 0, i64 undef, i64 2, i64 undef> to <16 x i16>) to <16 x i8>), i32 2), i8 0, i8 0, i8 0, i8 0, i8 0, i8 0, i8 0, i8 undef, i8 undef, i8 undef, i8 undef, i8 undef, i8 undef, i8 undef, i8 undef> to <2 x i64>)
+; CHECK-NEXT:    ret <2 x i64> zeroinitializer
 ;
   %1 = tail call <2 x i64> @llvm.x86.sse4a.extrqi(<2 x i64> bitcast (<16 x i8> trunc (<16 x i16> bitcast (<4 x i64> <i64 0, i64 undef, i64 2, i64 undef> to <16 x i16>) to <16 x i8>) to <2 x i64>), i8 8, i8 16)
   ret <2 x i64> %1
@@ -179,7 +178,7 @@ define <2 x i64> @test_insertq_constant_undef(<2 x i64> %x, <2 x i64> %y) {
 
 define <2 x i64> @test_insertq_call_constexpr(<2 x i64> %x) {
 ; CHECK-LABEL: @test_insertq_call_constexpr(
-; CHECK-NEXT:    [[TMP1:%.*]] = tail call <2 x i64> @llvm.x86.sse4a.insertq(<2 x i64> %x, <2 x i64> bitcast (<16 x i8> trunc (<16 x i16> bitcast (<4 x i64> <i64 0, i64 undef, i64 2, i64 undef> to <16 x i16>) to <16 x i8>) to <2 x i64>))
+; CHECK-NEXT:    [[TMP1:%.*]] = call <2 x i64> @llvm.x86.sse4a.insertqi(<2 x i64> %x, <2 x i64> <i64 0, i64 undef>, i8 2, i8 0)
 ; CHECK-NEXT:    ret <2 x i64> [[TMP1]]
 ;
   %1 = tail call <2 x i64> @llvm.x86.sse4a.insertq(<2 x i64> %x, <2 x i64> bitcast (<16 x i8> trunc (<16 x i16> bitcast (<4 x i64> <i64 0, i64 undef, i64 2, i64 undef> to <16 x i16>) to <16 x i8>) to <2 x i64>))
@@ -224,7 +223,7 @@ define <2 x i64> @test_insertqi_constant(<2 x i64> %v, <2 x i64> %i) {
 
 define <2 x i64> @test_insertqi_call_constexpr(<2 x i64> %x) {
 ; CHECK-LABEL: @test_insertqi_call_constexpr(
-; CHECK-NEXT:    [[TMP1:%.*]] = tail call <2 x i64> @llvm.x86.sse4a.insertqi(<2 x i64> %x, <2 x i64> bitcast (<16 x i8> trunc (<16 x i16> bitcast (<4 x i64> <i64 0, i64 undef, i64 2, i64 undef> to <16 x i16>) to <16 x i8>) to <2 x i64>), i8 48, i8 3)
+; CHECK-NEXT:    [[TMP1:%.*]] = tail call <2 x i64> @llvm.x86.sse4a.insertqi(<2 x i64> %x, <2 x i64> <i64 0, i64 undef>, i8 48, i8 3)
 ; CHECK-NEXT:    ret <2 x i64> [[TMP1]]
 ;
   %1 = tail call <2 x i64> @llvm.x86.sse4a.insertqi(<2 x i64> %x, <2 x i64> bitcast (<16 x i8> trunc (<16 x i16> bitcast (<4 x i64> <i64 0, i64 undef, i64 2, i64 undef> to <16 x i16>) to <16 x i8>) to <2 x i64>), i8 48, i8 3)
diff --git a/llvm/test/Transforms/InstSimplify/bitcast-vector-fold.ll b/llvm/test/Transforms/InstSimplify/bitcast-vector-fold.ll
index 126aba63ecbe..c8c390ea6be4 100644
--- a/llvm/test/Transforms/InstSimplify/bitcast-vector-fold.ll
+++ b/llvm/test/Transforms/InstSimplify/bitcast-vector-fold.ll
@@ -126,7 +126,7 @@ define <2 x double> @foo6() {
 
 define <4 x i32> @bitcast_constexpr_4i32_2i64_u2() {
 ; CHECK-LABEL: @bitcast_constexpr_4i32_2i64_u2(
-; CHECK-NEXT:    ret <4 x i32> bitcast (<2 x i64> <i64 undef, i64 2> to <4 x i32>)
+; CHECK-NEXT:    ret <4 x i32> <i32 undef, i32 undef, i32 2, i32 0>
 ;
   %cast = bitcast <2 x i64><i64 undef, i64 2> to <4 x i32>
   ret <4 x i32> %cast
@@ -134,7 +134,7 @@ define <4 x i32> @bitcast_constexpr_4i32_2i64_u2() {
 
 define <4 x i32> @bitcast_constexpr_4i32_2i64_1u() {
 ; CHECK-LABEL: @bitcast_constexpr_4i32_2i64_1u(
-; CHECK-NEXT:    ret <4 x i32> bitcast (<2 x i64> <i64 1, i64 undef> to <4 x i32>)
+; CHECK-NEXT:    ret <4 x i32> <i32 1, i32 0, i32 undef, i32 undef>
 ;
   %cast = bitcast <2 x i64><i64 1, i64 undef> to <4 x i32>
   ret <4 x i32> %cast
@@ -142,7 +142,7 @@ define <4 x i32> @bitcast_constexpr_4i32_2i64_1u() {
 
 define <4 x i32> @bitcast_constexpr_4i32_2i64() {
 ; CHECK-LABEL: @bitcast_constexpr_4i32_2i64(
-; CHECK-NEXT:    ret <4 x i32> bitcast (<2 x i64> <i64 undef, i64 2> to <4 x i32>)
+; CHECK-NEXT:    ret <4 x i32> <i32 undef, i32 undef, i32 2, i32 0>
 ;
   %cast = bitcast <2 x i64><i64 undef, i64 2> to <4 x i32>
   ret <4 x i32> %cast
@@ -150,7 +150,7 @@ define <4 x i32> @bitcast_constexpr_4i32_2i64() {
 
 define <8 x i16> @bitcast_constexpr_8i16_2i64_u2() {
 ; CHECK-LABEL: @bitcast_constexpr_8i16_2i64_u2(
-; CHECK-NEXT:    ret <8 x i16> bitcast (<2 x i64> <i64 undef, i64 2> to <8 x i16>)
+; CHECK-NEXT:    ret <8 x i16> <i16 undef, i16 undef, i16 undef, i16 undef, i16 2, i16 0, i16 0, i16 0>
 ;
   %cast = bitcast <2 x i64><i64 undef, i64 2> to <8 x i16>
   ret <8 x i16> %cast
@@ -158,7 +158,7 @@ define <8 x i16> @bitcast_constexpr_8i16_2i64_u2() {
 
 define <8 x i16> @bitcast_constexpr_8i16_2i64_1u() {
 ; CHECK-LABEL: @bitcast_constexpr_8i16_2i64_1u(
-; CHECK-NEXT:    ret <8 x i16> bitcast (<2 x i64> <i64 1, i64 undef> to <8 x i16>)
+; CHECK-NEXT:    ret <8 x i16> <i16 1, i16 0, i16 0, i16 0, i16 undef, i16 undef, i16 undef, i16 undef>
 ;
   %cast = bitcast <2 x i64><i64 1, i64 undef> to <8 x i16>
   ret <8 x i16> %cast
@@ -166,7 +166,7 @@ define <8 x i16> @bitcast_constexpr_8i16_2i64_1u() {
 
 define <8 x i16> @bitcast_constexpr_8i16_2i64_u65536() {
 ; CHECK-LABEL: @bitcast_constexpr_8i16_2i64_u65536(
-; CHECK-NEXT:    ret <8 x i16> bitcast (<2 x i64> <i64 undef, i64 65536> to <8 x i16>)
+; CHECK-NEXT:    ret <8 x i16> <i16 undef, i16 undef, i16 undef, i16 undef, i16 0, i16 1, i16 0, i16 0>
 ;
   %cast = bitcast <2 x i64><i64 undef, i64 65536> to <8 x i16>
   ret <8 x i16> %cast
@@ -174,7 +174,7 @@ define <8 x i16> @bitcast_constexpr_8i16_2i64_u65536() {
 
 define <16 x i8> @bitcast_constexpr_16i8_2i64_u2() {
 ; CHECK-LABEL: @bitcast_constexpr_16i8_2i64_u2(
-; CHECK-NEXT:    ret <16 x i8> bitcast (<2 x i64> <i64 undef, i64 2> to <16 x i8>)
+; CHECK-NEXT:    ret <16 x i8> <i8 undef, i8 undef, i8 undef, i8 undef, i8 undef, i8 undef, i8 undef, i8 undef, i8 2, i8 0, i8 0, i8 0, i8 0, i8 0, i8 0, i8 0>
 ;
   %cast = bitcast <2 x i64><i64 undef, i64 2> to <16 x i8>
   ret <16 x i8> %cast
@@ -182,7 +182,7 @@ define <16 x i8> @bitcast_constexpr_16i8_2i64_u2() {
 
 define <16 x i8> @bitcast_constexpr_16i8_2i64_256u() {
 ; CHECK-LABEL: @bitcast_constexpr_16i8_2i64_256u(
-; CHECK-NEXT:    ret <16 x i8> bitcast (<2 x i64> <i64 256, i64 undef> to <16 x i8>)
+; CHECK-NEXT:    ret <16 x i8> <i8 0, i8 1, i8 0, i8 0, i8 0, i8 0, i8 0, i8 0, i8 undef, i8 undef, i8 undef, i8 undef, i8 undef, i8 undef, i8 undef, i8 undef>
 ;
   %cast = bitcast <2 x i64><i64 256, i64 undef> to <16 x i8>
   ret <16 x i8> %cast
@@ -190,7 +190,7 @@ define <16 x i8> @bitcast_constexpr_16i8_2i64_256u() {
 
 define <16 x i8> @bitcast_constexpr_16i8_2i64_u256() {
 ; CHECK-LABEL: @bitcast_constexpr_16i8_2i64_u256(
-; CHECK-NEXT:    ret <16 x i8> bitcast (<2 x i64> <i64 undef, i64 256> to <16 x i8>)
+; CHECK-NEXT:    ret <16 x i8> <i8 undef, i8 undef, i8 undef, i8 undef, i8 undef, i8 undef, i8 undef, i8 undef, i8 0, i8 1, i8 0, i8 0, i8 0, i8 0, i8 0, i8 0>
 ;
   %cast = bitcast <2 x i64><i64 undef, i64 256> to <16 x i8>
   ret <16 x i8> %cast
@@ -198,7 +198,7 @@ define <16 x i8> @bitcast_constexpr_16i8_2i64_u256() {
 
 define <8 x i16> @bitcast_constexpr_8i16_4i32_uu22() {
 ; CHECK-LABEL: @bitcast_constexpr_8i16_4i32_uu22(
-; CHECK-NEXT:    ret <8 x i16> bitcast (<4 x i32> <i32 undef, i32 undef, i32 2, i32 2> to <8 x i16>)
+; CHECK-NEXT:    ret <8 x i16> <i16 undef, i16 undef, i16 undef, i16 undef, i16 2, i16 0, i16 2, i16 0>
 ;
   %cast = bitcast <4 x i32><i32 undef, i32 undef, i32 2, i32 2> to <8 x i16>
   ret <8 x i16> %cast
@@ -206,7 +206,7 @@ define <8 x i16> @bitcast_constexpr_8i16_4i32_uu22() {
 
 define <8 x i16> @bitcast_constexpr_8i16_4i32_10uu() {
 ; CHECK-LABEL: @bitcast_constexpr_8i16_4i32_10uu(
-; CHECK-NEXT:    ret <8 x i16> bitcast (<4 x i32> <i32 1, i32 0, i32 undef, i32 undef> to <8 x i16>)
+; CHECK-NEXT:    ret <8 x i16> <i16 1, i16 0, i16 0, i16 0, i16 undef, i16 undef, i16 undef, i16 undef>
 ;
   %cast = bitcast <4 x i32><i32 1, i32 0, i32 undef, i32 undef> to <8 x i16>
   ret <8 x i16> %cast
@@ -214,7 +214,7 @@ define <8 x i16> @bitcast_constexpr_8i16_4i32_10uu() {
 
 define <8 x i16> @bitcast_constexpr_8i16_4i32_u257u256() {
 ; CHECK-LABEL: @bitcast_constexpr_8i16_4i32_u257u256(
-; CHECK-NEXT:    ret <8 x i16> bitcast (<4 x i32> <i32 undef, i32 65536, i32 undef, i32 65536> to <8 x i16>)
+; CHECK-NEXT:    ret <8 x i16> <i16 undef, i16 undef, i16 0, i16 1, i16 undef, i16 undef, i16 0, i16 1>
 ;
   %cast = bitcast <4 x i32><i32 undef, i32 65536, i32 undef, i32 65536> to <8 x i16>
   ret <8 x i16> %cast
@@ -222,7 +222,7 @@ define <8 x i16> @bitcast_constexpr_8i16_4i32_u257u256() {
 
 define <16 x i8> @bitcast_constexpr_16i8_4i32_u2u2() {
 ; CHECK-LABEL: @bitcast_constexpr_16i8_4i32_u2u2(
-; CHECK-NEXT:    ret <16 x i8> bitcast (<4 x i32> <i32 undef, i32 2, i32 undef, i32 2> to <16 x i8>)
+; CHECK-NEXT:    ret <16 x i8> <i8 undef, i8 undef, i8 undef, i8 undef, i8 2, i8 0, i8 0, i8 0, i8 undef, i8 undef, i8 undef, i8 undef, i8 2, i8 0, i8 0, i8 0>
 ;
   %cast = bitcast <4 x i32><i32 undef, i32 2, i32 undef, i32 2> to <16 x i8>
   ret <16 x i8> %cast
@@ -230,7 +230,7 @@ define <16 x i8> @bitcast_constexpr_16i8_4i32_u2u2() {
 
 define <16 x i8> @bitcast_constexpr_16i8_4i32_1u1u() {
 ; CHECK-LABEL: @bitcast_constexpr_16i8_4i32_1u1u(
-; CHECK-NEXT:    ret <16 x i8> bitcast (<4 x i32> <i32 1, i32 undef, i32 1, i32 undef> to <16 x i8>)
+; CHECK-NEXT:    ret <16 x i8> <i8 1, i8 0, i8 0, i8 0, i8 undef, i8 undef, i8 undef, i8 undef, i8 1, i8 0, i8 0, i8 0, i8 undef, i8 undef, i8 undef, i8 undef>
 ;
   %cast = bitcast <4 x i32><i32 1, i32 undef, i32 1, i32 undef> to <16 x i8>
   ret <16 x i8> %cast
@@ -238,7 +238,7 @@ define <16 x i8> @bitcast_constexpr_16i8_4i32_1u1u() {
 
 define <16 x i8> @bitcast_constexpr_16i8_4i32_u256uu() {
 ; CHECK-LABEL: @bitcast_constexpr_16i8_4i32_u256uu(
-; CHECK-NEXT:    ret <16 x i8> bitcast (<4 x i32> <i32 undef, i32 256, i32 undef, i32 undef> to <16 x i8>)
+; CHECK-NEXT:    ret <16 x i8> <i8 undef, i8 undef, i8 undef, i8 undef, i8 0, i8 1, i8 0, i8 0, i8 undef, i8 undef, i8 undef, i8 undef, i8 undef, i8 undef, i8 undef, i8 undef>
 ;
   %cast = bitcast <4 x i32><i32 undef, i32 256, i32 undef, i32 undef> to <16 x i8>
   ret <16 x i8> %cast
@@ -246,7 +246,7 @@ define <16 x i8> @bitcast_constexpr_16i8_4i32_u256uu() {
 
 define <16 x i8> @bitcast_constexpr_16i8_8i16_u2u2u2u2() {
 ; CHECK-LABEL: @bitcast_constexpr_16i8_8i16_u2u2u2u2(
-; CHECK-NEXT:    ret <16 x i8> bitcast (<8 x i16> <i16 undef, i16 2, i16 undef, i16 2, i16 undef, i16 2, i16 undef, i16 2> to <16 x i8>)
+; CHECK-NEXT:    ret <16 x i8> <i8 undef, i8 undef, i8 2, i8 0, i8 undef, i8 undef, i8 2, i8 0, i8 undef, i8 undef, i8 2, i8 0, i8 undef, i8 undef, i8 2, i8 0>
 ;
   %cast = bitcast <8 x i16><i16 undef, i16 2, i16 undef, i16 2, i16 undef, i16 2, i16 undef, i16 2> to <16 x i8>
   ret <16 x i8> %cast
@@ -254,7 +254,7 @@ define <16 x i8> @bitcast_constexpr_16i8_8i16_u2u2u2u2() {
 
 define <16 x i8> @bitcast_constexpr_16i8_8i16_1u1u1u1u() {
 ; CHECK-LABEL: @bitcast_constexpr_16i8_8i16_1u1u1u1u(
-; CHECK-NEXT:    ret <16 x i8> bitcast (<8 x i16> <i16 1, i16 undef, i16 1, i16 undef, i16 1, i16 undef, i16 1, i16 undef> to <16 x i8>)
+; CHECK-NEXT:    ret <16 x i8> <i8 1, i8 0, i8 undef, i8 undef, i8 1, i8 0, i8 undef, i8 undef, i8 1, i8 0, i8 undef, i8 undef, i8 1, i8 0, i8 undef, i8 undef>
 ;
   %cast = bitcast <8 x i16><i16 1, i16 undef, i16 1, i16 undef, i16 1, i16 undef, i16 1, i16 undef> to <16 x i8>
   ret <16 x i8> %cast
@@ -262,7 +262,7 @@ define <16 x i8> @bitcast_constexpr_16i8_8i16_1u1u1u1u() {
 
 define <16 x i8> @bitcast_constexpr_16i8_8i16_u256uuu256uu() {
 ; CHECK-LABEL: @bitcast_constexpr_16i8_8i16_u256uuu256uu(
-; CHECK-NEXT:    ret <16 x i8> bitcast (<8 x i16> <i16 undef, i16 256, i16 undef, i16 undef, i16 undef, i16 256, i16 undef, i16 undef> to <16 x i8>)
+; CHECK-NEXT:    ret <16 x i8> <i8 undef, i8 undef, i8 0, i8 1, i8 undef, i8 undef, i8 undef, i8 undef, i8 undef, i8 undef, i8 0, i8 1, i8 undef, i8 undef, i8 undef, i8 undef>
 ;
   %cast = bitcast <8 x i16><i16 undef, i16 256, i16 undef, i16 undef, i16 undef, i16 256, i16 undef, i16 undef> to <16 x i8>
   ret <16 x i8> %cast