Index: llvm/trunk/lib/Target/AArch64/AArch64ISelLowering.cpp
===================================================================
--- llvm/trunk/lib/Target/AArch64/AArch64ISelLowering.cpp
+++ llvm/trunk/lib/Target/AArch64/AArch64ISelLowering.cpp
@@ -9935,6 +9935,15 @@
   if (LD->getOpcode() != ISD::LOAD)
     return SDValue();
 
+  // The vector lane must be a constant in the LD1LANE opcode.
+  SDValue Lane;
+  if (IsLaneOp) {
+    Lane = N->getOperand(2);
+    auto *LaneC = dyn_cast<ConstantSDNode>(Lane);
+    if (!LaneC || LaneC->getZExtValue() >= VT.getVectorNumElements())
+      return SDValue();
+  }
+
   LoadSDNode *LoadSDN = cast<LoadSDNode>(LD);
   EVT MemVT = LoadSDN->getMemoryVT();
   // Check if memory operand is the same type as the vector element.
@@ -9991,7 +10000,7 @@
     Ops.push_back(LD->getOperand(0));  // Chain
     if (IsLaneOp) {
       Ops.push_back(Vector);           // The vector to be inserted
-      Ops.push_back(N->getOperand(2)); // The lane to be inserted in the vector
+      Ops.push_back(Lane);             // The lane to be inserted in the vector
     }
     Ops.push_back(Addr);
     Ops.push_back(Inc);
Index: llvm/trunk/test/CodeGen/AArch64/arm64-indexed-vector-ldst-2.ll
===================================================================
--- llvm/trunk/test/CodeGen/AArch64/arm64-indexed-vector-ldst-2.ll
+++ llvm/trunk/test/CodeGen/AArch64/arm64-indexed-vector-ldst-2.ll
@@ -28,6 +28,28 @@
   ret void
 }
 
+; Avoid an assert/bad codegen in LD1LANEPOST lowering by not forming
+; LD1LANEPOST ISD nodes with a non-constant lane index.
+define <4 x i32> @f2(i32 *%p, <4 x i1> %m, <4 x i32> %v1, <4 x i32> %v2, i32 %idx) {
+  %L0 = load i32, i32* %p
+  %p1 = getelementptr i32, i32* %p, i64 1
+  %L1 = load i32, i32* %p1
+  %v = select <4 x i1> %m, <4 x i32> %v1, <4 x i32> %v2
+  %vret = insertelement <4 x i32> %v, i32 %L0, i32 %idx
+  store i32 %L1, i32 *%p
+  ret <4 x i32> %vret
+}
+
+; Check that a cycle is avoided during isel between the LD1LANEPOST instruction and the load of %L1.
+define <4 x i32> @f3(i32 *%p, <4 x i1> %m, <4 x i32> %v1, <4 x i32> %v2) {
+  %L0 = load i32, i32* %p
+  %p1 = getelementptr i32, i32* %p, i64 1
+  %L1 = load i32, i32* %p1
+  %v = select <4 x i1> %m, <4 x i32> %v1, <4 x i32> %v2
+  %vret = insertelement <4 x i32> %v, i32 %L0, i32 %L1
+  ret <4 x i32> %vret
+}
+
 ; Function Attrs: nounwind readnone
 declare i64 @llvm.objectsize.i64.p0i8(i8*, i1) #1