diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
@@ -139,6 +139,15 @@
 //===----------------------------------------------------------------------===//
 
 bool ISD::isConstantSplatVector(const SDNode *N, APInt &SplatVal) {
+  if (N->getOpcode() == ISD::SPLAT_VECTOR) {
+    unsigned EltSize =
+        N->getValueType(0).getVectorElementType().getSizeInBits();
+    if (auto *Op0 = dyn_cast<ConstantSDNode>(N->getOperand(0))) {
+      SplatVal = Op0->getAPIntValue().truncOrSelf(EltSize);
+      return true;
+    }
+  }
+
   auto *BV = dyn_cast<BuildVectorSDNode>(N);
   if (!BV)
     return false;
diff --git a/llvm/test/CodeGen/AArch64/sve-gep.ll b/llvm/test/CodeGen/AArch64/sve-gep.ll
--- a/llvm/test/CodeGen/AArch64/sve-gep.ll
+++ b/llvm/test/CodeGen/AArch64/sve-gep.ll
@@ -105,11 +105,9 @@
 ; CHECK-LABEL: scalable_of_scalable_1:
 ; CHECK:       // %bb.0:
 ; CHECK-NEXT:    rdvl x8, #1
-; CHECK-NEXT:    mov z1.d, #1 // =0x1
-; CHECK-NEXT:    mov z0.d, x0
-; CHECK-NEXT:    mov z2.d, x8
-; CHECK-NEXT:    ptrue p0.d
-; CHECK-NEXT:    mla z0.d, p0/m, z2.d, z1.d
+; CHECK-NEXT:    mov z0.d, x8
+; CHECK-NEXT:    mov z1.d, x0
+; CHECK-NEXT:    add z0.d, z1.d, z0.d
 ; CHECK-NEXT:    ret
   %idx = shufflevector <vscale x 2 x i64> insertelement (<vscale x 2 x i64> undef, i64 1, i32 0), <vscale x 2 x i64> zeroinitializer, <vscale x 2 x i32> zeroinitializer
   %d = getelementptr <vscale x 2 x i64>, <vscale x 2 x i64>* %base, <vscale x 2 x i64> %idx
@@ -120,10 +118,8 @@
 ; CHECK-LABEL: scalable_of_scalable_2:
 ; CHECK:       // %bb.0:
 ; CHECK-NEXT:    rdvl x8, #1
-; CHECK-NEXT:    mov z1.d, #1 // =0x1
-; CHECK-NEXT:    mov z2.d, x8
-; CHECK-NEXT:    ptrue p0.d
-; CHECK-NEXT:    mla z0.d, p0/m, z2.d, z1.d
+; CHECK-NEXT:    mov z1.d, x8
+; CHECK-NEXT:    add z0.d, z0.d, z1.d
 ; CHECK-NEXT:    ret
   %idx = shufflevector <vscale x 2 x i64> insertelement (<vscale x 2 x i64> undef, i64 1, i32 0), <vscale x 2 x i64> zeroinitializer, <vscale x 2 x i32> zeroinitializer
   %d = getelementptr <vscale x 2 x i64>, <vscale x 2 x <vscale x 2 x i64>*> %base, <vscale x 2 x i64> %idx