[wasm]implement simd lowering for f32x4->i32x4, i32x4 min/max and shift instructions

src/compiler/simd-scalar-lowering.h

 // Copyright 2016 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_COMPILER_SIMD_SCALAR_LOWERING_H_
 #define V8_COMPILER_SIMD_SCALAR_LOWERING_H_
 
 #include "src/compiler/common-operator.h"
 #include "src/compiler/graph.h"
 #include "src/compiler/machine-operator.h"
@@ skipping 43 matching lines @@
   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 input_rep_type, const Operator* op);
   void LowerUnaryOp(Node* node, SimdType input_rep_type, const Operator* op);
+  void LowerIntMinMax(Node* node, const Operator* op, bool is_max);
+  void LowerConvertFromFloat(Node* node, bool is_signed);
+  void LowerShiftOp(Node* node, const Operator* op);
 
   struct NodeState {
     Node* node;
     int input_index;
   };
 
   Zone* zone_;
   Graph* const graph_;
   MachineOperatorBuilder* machine_;
   CommonOperatorBuilder* common_;
   NodeMarker<State> state_;
   ZoneDeque<NodeState> stack_;
   Replacement* replacements_;
   Signature<MachineRepresentation>* signature_;
   Node* placeholder_;
   int parameter_count_after_lowering_;
 };
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_COMPILER_SIMD_SCALAR_LOWERING_H_