!7945 Add self-realized Softmax and LayerNorm

Merge pull request !7945 from wangjun/master

model_zoo/official/nlp/gpt/src/gpt.py

@@ -25,6 +25,61 @@ from mindspore.common.initializer import TruncatedNormal, initializer
 from mindspore.ops import operations as P
 from mindspore.ops import functional as F
 
+class LayerNorm(nn.Cell):
+    """
+    Layer Normalization
+
+    Args:
+        normalized_shape: the corresponding shape of the normalized axes
+        eps: epsilon, a small number avoiding zero division
+
+    Inputs:
+        x: input tensor
+
+    Returns:
+        rescaled_output: Tensor, returned tensor after layernorm
+    """
+    def __init__(self, normalized_shape, eps=1e-5):
+        super(LayerNorm, self).__init__()
+        self.gamma = Parameter(initializer('ones', normalized_shape), name="gamma")
+        self.beta = Parameter(initializer('zeros', normalized_shape), name="beta")
+        self.mean = P.ReduceMean(keep_dims=True)
+        self.eps = eps
+
+    def construct(self, x):
+        mean = self.mean(x, -1)
+        variance = self.mean(F.square(x - mean))
+        output = (x - mean) / F.sqrt(variance + self.eps)
+        rescaled_output = output * self.gamma + self.beta
+        return rescaled_output
+
+class Softmax(nn.Cell):
+    """
+    softmax realization
+
+    Args:
+        axis: the axis to be applied softmax
+
+    Inputs:
+        x: input tensor
+
+    Returns:
+        output: Tensor, returned tensor after softmax
+    """
+    def __init__(self, axis=-1):
+        super(Softmax, self).__init__()
+        self.max = P.ArgMaxWithValue(axis=axis, keep_dims=True)
+        self.sum = P.ReduceSum(keep_dims=True)
+        self.axis = axis
+
+    def construct(self, x):
+        _, max_value = self.max(x)
+        exp_x = F.tensor_pow(np.e, x - max_value)
+        sum_x = self.sum(exp_x, self.axis)
+        output = exp_x / sum_x
+        return output
+
+
 class Mapping(nn.Cell):
     """
     A mapping function with a 3d input
@@ -162,7 +217,6 @@ class Attention(nn.Cell):
     def __init__(self, config, scale=1.0, layer_idx=None):
         super(Attention, self).__init__()
         self.get_attention_mask = AttentionMask(config)
-        self.expand_mapping = Mapping(config.embedding_size, 3*config.embedding_size, config.compute_dtype)
         self.projection = Mapping(config.embedding_size, config.embedding_size, config.compute_dtype, scale)
         self.split = P.Split(axis=-1, output_num=3)
         self.transpose = P.Transpose()
@@ -182,7 +236,6 @@ class Attention(nn.Cell):
         self.use_past = config.use_past
         self.dropout = nn.Dropout(1-config.dropout_rate)
         self.prob_dropout = nn.Dropout(1-config.dropout_rate)
-        self.softmax = nn.Softmax()
 
         self.dense1 = nn.Dense(config.embedding_size, config.embedding_size).to_float(config.compute_dtype)
         self.dense2 = nn.Dense(config.embedding_size, config.embedding_size).to_float(config.compute_dtype)
@@ -285,9 +338,7 @@ class Attention(nn.Cell):
         attention_scores = adder + score
 
         attention_scores = P.Cast()(attention_scores, ori_dtype)
-        shape = F.shape(attention_scores)
-        attention_probs = nn.Softmax()(F.reshape(attention_scores, (-1, shape[-1])))
-        attention_probs = F.reshape(attention_probs, shape)
+        attention_probs = Softmax()(attention_scores)
 
         attention_probs = self.prob_dropout(attention_probs)
         weighted_values = self.batch_matmul(attention_probs, value)
@@ -313,9 +364,9 @@ class Block(nn.Cell):
     def __init__(self, config, layer_idx):
         super(Block, self).__init__()
         scale = 1 / math.sqrt(2.0*layer_idx)
-        self.layernorm1 = nn.LayerNorm((config.embedding_size,)).to_float(config.compute_dtype)
+        self.layernorm1 = LayerNorm((config.embedding_size,)).to_float(config.compute_dtype)
         self.attention = Attention(config, scale, layer_idx)
-        self.layernorm2 = nn.LayerNorm((config.embedding_size,)).to_float(config.compute_dtype)
+        self.layernorm2 = LayerNorm((config.embedding_size,)).to_float(config.compute_dtype)
         self.output = Output(config, scale)
         self.post_layernorm_residual = config.post_layernorm_residual
 
@@ -362,7 +413,7 @@ class GPT_Model(nn.Cell):
         self.blocks = nn.CellList()
         for i in range(config.num_layers):
             self.blocks.append(Block(config, i+1))
-        self.layernorm = nn.LayerNorm((config.embedding_size,)).to_float(config.compute_dtype)
+        self.layernorm = LayerNorm((config.embedding_size,)).to_float(config.compute_dtype)
         self.use_past = config.use_past
         self.past = tuple([None]*config.num_layers)
         self.num_layers = config.num_layers