diff --git a/llvm/lib/Target/AArch64/AArch64TargetTransformInfo.cpp b/llvm/lib/Target/AArch64/AArch64TargetTransformInfo.cpp
--- a/llvm/lib/Target/AArch64/AArch64TargetTransformInfo.cpp
+++ b/llvm/lib/Target/AArch64/AArch64TargetTransformInfo.cpp
@@ -2091,6 +2091,23 @@
     { ISD::BITCAST, MVT::nxv2i16, MVT::nxv2f16, 0 },
     { ISD::BITCAST, MVT::nxv4i16, MVT::nxv4f16, 0 },
     { ISD::BITCAST, MVT::nxv2i32, MVT::nxv2f32, 0 },
+
+    // Add cost for extending to illegal -too wide- scalable vectors.
+    // zero/sign extend are implemented by multiple unpack operations,
+    // where each operation has a cost of 1.
+    { ISD::ZERO_EXTEND, MVT::nxv16i16, MVT::nxv16i8, 2},
+    { ISD::ZERO_EXTEND, MVT::nxv16i32, MVT::nxv16i8, 6},
+    { ISD::ZERO_EXTEND, MVT::nxv16i64, MVT::nxv16i8, 14},
+    { ISD::ZERO_EXTEND, MVT::nxv8i32, MVT::nxv8i16, 2},
+    { ISD::ZERO_EXTEND, MVT::nxv8i64, MVT::nxv8i16, 6},
+    { ISD::ZERO_EXTEND, MVT::nxv4i64, MVT::nxv4i32, 2},
+
+    { ISD::SIGN_EXTEND, MVT::nxv16i16, MVT::nxv16i8, 2},
+    { ISD::SIGN_EXTEND, MVT::nxv16i32, MVT::nxv16i8, 6},
+    { ISD::SIGN_EXTEND, MVT::nxv16i64, MVT::nxv16i8, 14},
+    { ISD::SIGN_EXTEND, MVT::nxv8i32, MVT::nxv8i16, 2},
+    { ISD::SIGN_EXTEND, MVT::nxv8i64, MVT::nxv8i16, 6},
+    { ISD::SIGN_EXTEND, MVT::nxv4i64, MVT::nxv4i32, 2},
   };
 
   if (const auto *Entry = ConvertCostTableLookup(ConversionTbl, ISD,
diff --git a/llvm/test/Analysis/CostModel/AArch64/cast.ll b/llvm/test/Analysis/CostModel/AArch64/cast.ll
--- a/llvm/test/Analysis/CostModel/AArch64/cast.ll
+++ b/llvm/test/Analysis/CostModel/AArch64/cast.ll
@@ -858,8 +858,8 @@
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 2 for instruction: %v13 = zext <4 x i32> %loadv4i32 to <4 x i64>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %v14 = sext <vscale x 2 x i32> %loadnxv2i32 to <vscale x 2 x i64>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %v15 = zext <vscale x 2 x i32> %loadnxv2i32 to <vscale x 2 x i64>
-; CHECK-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %v16 = sext <vscale x 4 x i32> %loadnxv4i32 to <vscale x 4 x i64>
-; CHECK-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %v17 = zext <vscale x 4 x i32> %loadnxv4i32 to <vscale x 4 x i64>
+; CHECK-NEXT:  Cost Model: Found an estimated cost of 2 for instruction: %v16 = sext <vscale x 4 x i32> %loadnxv4i32 to <vscale x 4 x i64>
+; CHECK-NEXT:  Cost Model: Found an estimated cost of 2 for instruction: %v17 = zext <vscale x 4 x i32> %loadnxv4i32 to <vscale x 4 x i64>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: ret i32 undef
 ;
   %loadi8 = load i8, ptr undef
diff --git a/llvm/test/Analysis/CostModel/AArch64/sve-ext.ll b/llvm/test/Analysis/CostModel/AArch64/sve-ext.ll
new file mode 100644
--- /dev/null
+++ b/llvm/test/Analysis/CostModel/AArch64/sve-ext.ll
@@ -0,0 +1,37 @@
+; NOTE: Assertions have been autogenerated by utils/update_analyze_test_checks.py
+; RUN: opt -passes="print<cost-model>" 2>&1 -disable-output -mtriple aarch64-linux-gnu -mattr=+sve -S -o - < %s | FileCheck %s
+
+target triple = "aarch64-unknown-linux-gnu"
+
+define void @sve_ext() {
+; CHECK-LABEL: 'sve_ext'
+; CHECK-NEXT:  Cost Model: Found an estimated cost of 2 for instruction: %zext_nxv16_i8_to_i16 = zext <vscale x 16 x i8> undef to <vscale x 16 x i16>
+; CHECK-NEXT:  Cost Model: Found an estimated cost of 6 for instruction: %zext_nxv16_i8_to_i32 = zext <vscale x 16 x i8> undef to <vscale x 16 x i32>
+; CHECK-NEXT:  Cost Model: Found an estimated cost of 14 for instruction: %zext_nxv16_i8_to_i64 = zext <vscale x 16 x i8> undef to <vscale x 16 x i64>
+; CHECK-NEXT:  Cost Model: Found an estimated cost of 2 for instruction: %zext_nxv8_i16_to_i32 = zext <vscale x 8 x i16> undef to <vscale x 8 x i32>
+; CHECK-NEXT:  Cost Model: Found an estimated cost of 6 for instruction: %zext_nxv8_i16_to_i64 = zext <vscale x 8 x i16> undef to <vscale x 8 x i64>
+; CHECK-NEXT:  Cost Model: Found an estimated cost of 2 for instruction: %zext_nxv4_i32_to_i64 = zext <vscale x 4 x i32> undef to <vscale x 4 x i64>
+; CHECK-NEXT:  Cost Model: Found an estimated cost of 2 for instruction: %sext_nxv16_i8_to_i16 = sext <vscale x 16 x i8> undef to <vscale x 16 x i16>
+; CHECK-NEXT:  Cost Model: Found an estimated cost of 6 for instruction: %sext_nxv16_i8_to_i32 = sext <vscale x 16 x i8> undef to <vscale x 16 x i32>
+; CHECK-NEXT:  Cost Model: Found an estimated cost of 14 for instruction: %sext_nxv16_i8_to_i64 = sext <vscale x 16 x i8> undef to <vscale x 16 x i64>
+; CHECK-NEXT:  Cost Model: Found an estimated cost of 2 for instruction: %sext_nxv8_i16_to_i32 = sext <vscale x 8 x i16> undef to <vscale x 8 x i32>
+; CHECK-NEXT:  Cost Model: Found an estimated cost of 6 for instruction: %sext_nxv8_i16_to_i64 = sext <vscale x 8 x i16> undef to <vscale x 8 x i64>
+; CHECK-NEXT:  Cost Model: Found an estimated cost of 2 for instruction: %sext_nxv4_i32_to_i64 = sext <vscale x 4 x i32> undef to <vscale x 4 x i64>
+; CHECK-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: ret void
+;
+  %zext_nxv16_i8_to_i16 = zext <vscale x 16 x i8> undef to <vscale x 16 x i16>
+  %zext_nxv16_i8_to_i32 = zext <vscale x 16 x i8> undef to <vscale x 16 x i32>
+  %zext_nxv16_i8_to_i64 = zext <vscale x 16 x i8> undef to <vscale x 16 x i64>
+  %zext_nxv8_i16_to_i32 = zext <vscale x 8 x i16> undef to <vscale x 8 x i32>
+  %zext_nxv8_i16_to_i64 = zext <vscale x 8 x i16> undef to <vscale x 8 x i64>
+  %zext_nxv4_i32_to_i64 = zext <vscale x 4 x i32> undef to <vscale x 4 x i64>
+
+  %sext_nxv16_i8_to_i16 = sext <vscale x 16 x i8> undef to <vscale x 16 x i16>
+  %sext_nxv16_i8_to_i32 = sext <vscale x 16 x i8> undef to <vscale x 16 x i32>
+  %sext_nxv16_i8_to_i64 = sext <vscale x 16 x i8> undef to <vscale x 16 x i64>
+  %sext_nxv8_i16_to_i32 = sext <vscale x 8 x i16> undef to <vscale x 8 x i32>
+  %sext_nxv8_i16_to_i64 = sext <vscale x 8 x i16> undef to <vscale x 8 x i64>
+  %sext_nxv4_i32_to_i64 = sext <vscale x 4 x i32> undef to <vscale x 4 x i64>
+
+  ret void
+}
diff --git a/llvm/test/Analysis/CostModel/AArch64/sve-widening-instruction.ll b/llvm/test/Analysis/CostModel/AArch64/sve-widening-instruction.ll
--- a/llvm/test/Analysis/CostModel/AArch64/sve-widening-instruction.ll
+++ b/llvm/test/Analysis/CostModel/AArch64/sve-widening-instruction.ll
@@ -20,8 +20,8 @@
 
 define <vscale x 8 x i32> @widening_nxv8i16(<vscale x 8 x i16> %in1, <vscale x 8 x i16> %in2) {
 ; CHECK-LABEL: 'widening_nxv8i16'
-; CHECK-NEXT:  Cost Model: Found an estimated cost of 3 for instruction: %in1.ext = zext <vscale x 8 x i16> %in2 to <vscale x 8 x i32>
-; CHECK-NEXT:  Cost Model: Found an estimated cost of 3 for instruction: %in2.ext = zext <vscale x 8 x i16> %in2 to <vscale x 8 x i32>
+; CHECK-NEXT:  Cost Model: Found an estimated cost of 2 for instruction: %in1.ext = zext <vscale x 8 x i16> %in2 to <vscale x 8 x i32>
+; CHECK-NEXT:  Cost Model: Found an estimated cost of 2 for instruction: %in2.ext = zext <vscale x 8 x i16> %in2 to <vscale x 8 x i32>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 2 for instruction: %in.add = add <vscale x 8 x i32> %in1.ext, %in2.ext
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: ret <vscale x 8 x i32> %in.add
 ;