[wasm] implement simd lowering for replaceLane, load, store and test for phi

src/compiler/simd-scalar-lowering.h

Index: src/compiler/simd-scalar-lowering.h
diff --git a/src/compiler/simd-scalar-lowering.h b/src/compiler/simd-scalar-lowering.h
index 39449f4b9ff54d01a82fc25cf204bab9efa23812..c795c6b88bc1b169fc912d70df8f6f567a945d2f 100644
--- a/src/compiler/simd-scalar-lowering.h
+++ b/src/compiler/simd-scalar-lowering.h
@@ -31,6 +31,7 @@ class SimdScalarLowering {
   enum class SimdType : uint8_t { kInt32, kFloat32 };
 
   static const int kMaxLanes = 4;
+  static const int kLaneWidth = 16 / kMaxLanes;
 
   struct Replacement {
     Node* node[kMaxLanes];
@@ -53,6 +54,12 @@ class SimdScalarLowering {
   SimdType ReplacementType(Node* node);
   void PreparePhiReplacement(Node* phi);
   void SetLoweredType(Node* node, Node* output);
+  void GetIndexNodes(Node* index, Node** new_indices);
+  void LowerLoadOp(MachineRepresentation rep, Node* node,
+                   const Operator* load_op);
+  void LowerStoreOp(MachineRepresentation rep, Node* node,
+                    const Operator* store_op, SimdType rep_type);
+  void LowerBinaryOp(Node* node, SimdType rep_type, const Operator* op);
 
   struct NodeState {
     Node* node;