diff --git a/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp b/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp
--- a/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp
+++ b/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp
@@ -14094,6 +14094,8 @@
       // 8-bit sized types have a scaling factor of 1, thus a shift amount of 0.
       // Get the shift amount based on the scaling factor:
       // log2(sizeof(IdxTy)) - log2(8).
+      if (IdxTy->isScalableTy())
+        return false;
       uint64_t ShiftAmt =
           llvm::countr_zero(DL.getTypeStoreSizeInBits(IdxTy).getFixedValue()) -
           3;
diff --git a/llvm/test/Analysis/CostModel/AArch64/cost-scalable-vector-gep.ll b/llvm/test/Analysis/CostModel/AArch64/cost-scalable-vector-gep.ll
--- a/llvm/test/Analysis/CostModel/AArch64/cost-scalable-vector-gep.ll
+++ b/llvm/test/Analysis/CostModel/AArch64/cost-scalable-vector-gep.ll
@@ -1,3 +1,4 @@
+; NOTE: Assertions have been autogenerated by utils/update_analyze_test_checks.py UTC_ARGS: --version 2
 ; RUN: opt -passes="print<cost-model>" 2>&1 -disable-output -mtriple=aarch64--linux-gnu -mattr=+sve < %s | FileCheck %s
 
 ; This regression test is verifying that a GEP instruction performed on a
@@ -6,8 +7,22 @@
 
 target datalayout = "e-m:e-i8:8:32-i16:16:32-i64:64-i128:128-n32:64-S128"
 
-; CHECK: Cost Model: Found an estimated cost of 1 for instruction:   %retval = getelementptr
 define ptr @gep_scalable_vector(ptr %ptr) {
+; CHECK-LABEL: 'gep_scalable_vector'
+; CHECK-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %retval = getelementptr <vscale x 16 x i8>, ptr %ptr, i32 2
+; CHECK-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: ret ptr %retval
+;
   %retval = getelementptr <vscale x 16 x i8>, ptr %ptr, i32 2
   ret ptr %retval
 }
+
+define ptr @sext_gep(ptr %p, i32 %a) {
+; CHECK-LABEL: 'sext_gep'
+; CHECK-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %b = sext i32 %a to i64
+; CHECK-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %r = getelementptr <vscale x 8 x half>, ptr %p, i64 %b
+; CHECK-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: ret ptr %r
+;
+  %b = sext i32 %a to i64
+  %r = getelementptr <vscale x 8 x half>, ptr %p, i64 %b
+  ret ptr %r
+}