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
@@ -2059,6 +2059,15 @@
     { ISD::BITCAST, MVT::nxv2i16, MVT::nxv2f16, 0 },
     { ISD::BITCAST, MVT::nxv4i16, MVT::nxv4f16, 0 },
     { ISD::BITCAST, MVT::nxv2i32, MVT::nxv2f32, 0 },
+
+    // Add high cost for extending to illegal -too wide- scalable vectors.
+    { ISD::ZERO_EXTEND, MVT::nxv16i16, MVT::nxv16i8, 16},
+    { ISD::ZERO_EXTEND, MVT::nxv16i32, MVT::nxv16i8, 32},
+    { ISD::ZERO_EXTEND, MVT::nxv16i64, MVT::nxv16i8, 64},
+
+    { ISD::SIGN_EXTEND, MVT::nxv16i16, MVT::nxv16i8, 16},
+    { ISD::SIGN_EXTEND, MVT::nxv16i32, MVT::nxv16i8, 32},
+    { ISD::SIGN_EXTEND, MVT::nxv16i64, MVT::nxv16i8, 64},
   };
 
   if (const auto *Entry = ConvertCostTableLookup(ConversionTbl, ISD,
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 +1,25 @@
+; 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 16 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 32 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 64 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 16 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 32 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 64 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 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>
+
+  %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>
+
+  ret void
+}