[LegalizeTypes] Use getVectorElementCount to avoid crash of scalable vector.

[RKSimon]

test cases?

[RKSimon]

llvm/lib/CodeGen/SelectionDAG/LegalizeTypesGeneric.cpp

211

auto -> ElementCount

[jacquesguan]

Address comment.

[jacquesguan]

In D134718#3817513, @RKSimon wrote:

test cases?

Done.

llvm/lib/CodeGen/SelectionDAG/LegalizeTypesGeneric.cpp

211

Done.

[RKSimon]

LGTM

llvm/lib/CodeGen/SelectionDAG/LegalizeTypesGeneric.cpp

assert(Part.getValueType() == N->getValueType(0) &&
          "Type twice as big as expanded type not itself expanded!");
 
   GetPairElements(Part, Lo, Hi);
 }
 
 void DAGTypeLegalizer::ExpandRes_EXTRACT_VECTOR_ELT(SDNode *N, SDValue &Lo,
                                                     SDValue &Hi) {
   SDValue OldVec = N->getOperand(0);
-  unsigned OldElts = OldVec.getValueType().getVectorNumElements();
+  ElementCount OldEltCount = OldVec.getValueType().getVectorElementCount();
   EVT OldEltVT = OldVec.getValueType().getVectorElementType();
   SDLoc dl(N);
 
   // Convert to a vector of the expanded element type, for example
   // <3 x i64> -> <6 x i32>.
   EVT OldVT = N->getValueType(0);
   EVT NewVT = TLI.getTypeToTransformTo(*DAG.getContext(), OldVT);
 
   if (OldVT != OldEltVT) {
     // The result of EXTRACT_VECTOR_ELT may be larger than the element type of
     // the input vector.  If so, extend the elements of the input vector to the
     // same bitwidth as the result before expanding.
     assert(OldEltVT.bitsLT(OldVT) && "Result type smaller then element type!");
-    EVT NVecVT = EVT::getVectorVT(*DAG.getContext(), OldVT, OldElts);
+    EVT NVecVT = EVT::getVectorVT(*DAG.getContext(), OldVT, OldEltCount);
     OldVec = DAG.getNode(ISD::ANY_EXTEND, dl, NVecVT, N->getOperand(0));
   }
 
-  SDValue NewVec = DAG.getNode(ISD::BITCAST, dl,
-                               EVT::getVectorVT(*DAG.getContext(),
-                                                NewVT, 2*OldElts),
-                               OldVec);
+  SDValue NewVec = DAG.getNode(
+      ISD::BITCAST, dl,
+      EVT::getVectorVT(*DAG.getContext(), NewVT, OldEltCount * 2), OldVec);
 
   // Extract the elements at 2 * Idx and 2 * Idx + 1 from the new vector.
   SDValue Idx = N->getOperand(1);
 
   Idx = DAG.getNode(ISD::ADD, dl, Idx.getValueType(), Idx, Idx);
   Lo = DAG.getNode(ISD::EXTRACT_VECTOR_ELT, dl, NewVT, NewVec, Idx);
 
   Idx = DAG.getNode(ISD::ADD, dl, Idx.getValueType(), Idx,

llvm/test/CodeGen/RISCV/rvv/extractelt-int-rv32.ll

 ; CHECK-NEXT:    vs8r.v v16, (a1)
 ; CHECK-NEXT:    lw a0, 0(a0)
 ; CHECK-NEXT:    addi sp, s0, -64
 ; CHECK-NEXT:    addi sp, sp, 64
 ; CHECK-NEXT:    ret
   %r = extractelement <vscale x 32 x i32> %v, i32 %idx
   ret i32 %r
 }
+
+define i64 @extractelt_nxv16i64_0(<vscale x 16 x i64> %v) {
+; CHECK-LABEL: extractelt_nxv16i64_0:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    vsetivli zero, 1, e32, m8, ta, mu
+; CHECK-NEXT:    vslidedown.vi v16, v8, 1
+; CHECK-NEXT:    vmv.x.s a1, v16
+; CHECK-NEXT:    vmv.x.s a0, v8
+; CHECK-NEXT:    ret
+  %r = extractelement <vscale x 16 x i64> %v, i32 0
+  ret i64 %r
+}