[wasm] Implement I32x4ReplaceLane, I32x4Add, I32x4Sub.

src/compiler/simd-scalar-lowering.cc

Index: src/compiler/simd-scalar-lowering.cc
diff --git a/src/compiler/simd-scalar-lowering.cc b/src/compiler/simd-scalar-lowering.cc
index c5a94b4297e35d39d40714caf6bff06d9cf87554..7d8ec34b115b861591ebe2d6ebcceaa61832a15f 100644
--- a/src/compiler/simd-scalar-lowering.cc
+++ b/src/compiler/simd-scalar-lowering.cc
@@ -251,9 +251,7 @@ void SimdScalarLowering::LowerNode(Node* node) {
     }
 
     case IrOpcode::kInt32x4ExtractLane: {
-      Node* laneNode = node->InputAt(1);
-      DCHECK_EQ(laneNode->opcode(), IrOpcode::kInt32Constant);
-      int32_t lane = OpParameter<int32_t>(laneNode);
+      int32_t lane = OpParameter<int32_t>(node);
       Node* rep_node[kMaxLanes] = {
           GetReplacementsWithType(node->InputAt(0), rep_type)[lane], nullptr,
           nullptr, nullptr};
@@ -285,9 +283,7 @@ void SimdScalarLowering::LowerNode(Node* node) {
     }
 
     case IrOpcode::kFloat32x4ExtractLane: {
-      Node* laneNode = node->InputAt(1);
-      DCHECK_EQ(laneNode->opcode(), IrOpcode::kInt32Constant);
-      int32_t lane = OpParameter<int32_t>(laneNode);
+      int32_t lane = OpParameter<int32_t>(node);
       Node* rep_node[kMaxLanes] = {
           GetReplacementsWithType(node->InputAt(0), rep_type)[lane], nullptr,
           nullptr, nullptr};