speed up paddle.add paddle.nn.Linear (#32125)

* modify API nn.Bilinear's doc, test=develop

* speed up paddle.add paddle.nn.Linear, test=develop

* fix bug, test=develop

python/paddle/nn/functional/common.py

@@ -1446,11 +1446,12 @@ def linear(x, weight, bias=None, name=None):
           #     [2.1077576  2.1077576  2.1077576  2.1077576 ]]
     """
     if in_dygraph_mode():
-        pre_bias = _varbase_creator(dtype=x.dtype)
-        core.ops.matmul(x, weight, pre_bias, 'transpose_X', False,
-                        'transpose_Y', False, "alpha", 1)
-        return dygraph_utils._append_bias_in_dygraph(
-            pre_bias, bias, axis=len(x.shape) - 1)
+        pre_bias = core.ops.matmul_v2(x, weight)
+
+        if bias is None:
+            return pre_bias
+
+        return core.ops.elementwise_add(pre_bias, bias)
     else:
         helper = LayerHelper('linear', **locals())
         dtype = x.dtype

python/paddle/tensor/math.py

@@ -232,13 +232,11 @@ def add(x, y, name=None):
         print(z)  # [3., 8., 6. ]
 
     """
-    op_type = 'elementwise_add'
-    axis = -1
+
     if in_dygraph_mode():
-        return _elementwise_op_in_dygraph(
-            x, y, axis=axis, op_name=op_type)
+        return core.ops.elementwise_add(x, y)
 
-    return _elementwise_op(LayerHelper(op_type, **locals()))
+    return _elementwise_op(LayerHelper('elementwise_add', **locals()))
 
 
 @inplace_apis_in_dygraph_only