[Frontend] [Torch] [ONNX] GRU layer (#8781)

* GRU cell was implemented in common.py. GRU was supported on pytorch frontend side

* update GRU in common.py and onnx frontend

* fix issue related to GRU accuracy in pytorch and ONNX frontend

* small fixes and remove excess

* common GRU was additionaly updated. tuned pytorch GRU was strongly accelerated

* GRU cell in ONNX frontend was used from common.py. previous implementation was removed

* small fixes in comments

* fixes after review. GRU test was implemented for pytorch frontend

* tests for RNN layers was unified for pytorch frontend

Co-authored-by: Valery Chernov <valery.chernov@deelvin.com>

python/tvm/relay/frontend/common.py

@@ -658,6 +658,90 @@ def unbind(data, axis=0):
     return _expr.TupleWrapper(_expr.Tuple(ret), selections)
 
 
+def gru_cell(
+    input_seqs,
+    hidden_state,
+    w_inp,
+    w_hid,
+    b_inp=None,
+    b_hid=None,
+    rz_act=_op.sigmoid,
+    n_act=_op.tanh,
+    backwards=False,
+    linear_before_reset=True,
+):
+    """
+    Common implementation of GRU cell for all frontends of TVM
+    TODO(vvchernov): currently it is used by pytorch and ONNX. Extend for other frontends
+
+    Parameters
+    ----------
+    input_seqs : List[relay.Expr]
+        The sequence of input tensors
+        Input tensor should be 2d while issue #8412 is not resolved
+        Shape = (batch, feature_size)
+    hidden_state : relay.Expr
+        Hidden state. shape = (batch_size, hidden_size)
+    w_inp, w_hid : relay.Expr
+        weight matrices. wi shape = (3 * hidden_size, feature_size)
+        wh shape = (3 * hidden_size, hidden_size)
+        NOTE: wi = (w_ir|w_iz|w_in) for reset, update and new gates.
+        The order is important for correct GRU calculation!
+    b_inp, b_hid : relay.Expr
+        bias matrices. The same order of internal parts as for weights. shape = (3 * hidden_size)
+    r_act : relay.op
+        activation funtion for reset gate. it is sigmoid by default
+    z_act : relay.op
+        activation funtion for update gate. it is sigmoid by default
+    n_act : relay.op
+        activation funtion for new gate. it is tanh by default
+    backwards : bool
+        Flag for reverse pass of GRU
+
+    Returns
+    -------
+    result : List[relay.Expr], relay.Expr, relay.Expr
+        The sequence of computed result, final hidden and cell state
+    """
+
+    outputs_list = []
+    for x_t in input_seqs if not backwards else reversed(input_seqs):
+        xwt = _op.nn.dense(x_t, w_inp)
+        if linear_before_reset:
+            hwt = _op.nn.dense(hidden_state, w_hid)
+            if b_inp is not None and b_hid is not None:
+                xwt += b_inp
+                hwt += b_hid
+            i_r, i_z, i_n = _op.split(xwt, 3, axis=-1)
+            h_r, h_z, h_n = _op.split(hwt, 3, axis=-1)
+            r_gate = rz_act(i_r + h_r)
+            z_gate = rz_act(i_z + h_z)
+            n_gate = n_act(i_n + r_gate * h_n)
+        else:
+            i_r, i_z, i_n = _op.split(xwt, 3, axis=1)
+            w_hr, w_hz, w_hn = _op.split(w_hid, 3, axis=0)
+            r_gate = i_r + _op.nn.dense(hidden_state, w_hr)
+            z_gate = i_z + _op.nn.dense(hidden_state, w_hz)
+            if b_inp is not None and b_hid is not None:
+                b_ir, b_iz, b_in = _op.split(b_inp, 3, axis=-1)
+                b_hr, b_hz, b_hn = _op.split(b_hid, 3, axis=-1)
+                r_gate += b_ir + b_hr
+                z_gate += b_iz + b_hz
+                i_n += b_in
+                h_n = _op.nn.dense((r_gate * hidden_state), w_hn) + b_hn
+            else:
+                h_n = _op.nn.dense((r_gate * hidden_state), w_hn)
+            r_gate = rz_act(r_gate)
+            z_gate = rz_act(z_gate)
+            n_gate = n_act(i_n + h_n)
+
+        hidden_state = (hidden_state - n_gate) * z_gate + n_gate
+
+        outputs_list.append(hidden_state)  # [seq_num, (batch, hidden_size)]
+
+    return outputs_list, hidden_state
+
+
 def lstm_cell(
     input_seqs,
     hidden_state,

python/tvm/relay/frontend/onnx.py

@@ -47,6 +47,7 @@
     infer_value,
     new_var,
     unbind,
+    gru_cell,
     lstm_cell,
 )
 
@@ -2349,56 +2350,41 @@ class GRU(RNN):
     """Operator convert for GRU"""
 
     @classmethod
-    def generate_gru(
-        cls, X_steps, H_t, W, R, B, linear_before_reset, f_act, g_act, W_dtype, backwards=False
+    def bidir_gru_cell(
+        cls,
+        input_seqs,
+        weight_dicts,
+        acts,
     ):
-        """Create an unrolled gru loop.
-
-        See https://github.com/onnx/onnx/blob/master/docs/Operators.md for math.
         """
-        h_list = []
-        seq_length = len(X_steps)
-        for i in range(seq_length):
-            step = X_steps[i] if not backwards else X_steps[seq_length - (i + 1)]
-            step = _op.squeeze(step, axis=[0])
-            current = _op.nn.dense(step, W)
-            cz, cr, ch = _op.split(current, 3, axis=1)
-            rz, rr, rh = _op.split(R, 3, axis=0)
-            z = cz + _op.nn.dense(H_t, rz)
-            r = cr + _op.nn.dense(H_t, rr)
-            if B is not None:
-                WB, RB = _op.split(B, 2)
-                wbz, wbr, wbh = _op.split(WB, 3, axis=-1)
-                rbz, rbr, rbh = _op.split(RB, 3, axis=-1)
-                z += wbz + rbz
-                r += wbr + rbr
-                if linear_before_reset:
-                    h = ch + (r * (_op.nn.dense(H_t, rh) + rbh)) + wbh
-                else:
-                    h = ch + _op.nn.dense((r * H_t), rh) + wbh + rbh
-            else:
-                if linear_before_reset:
-                    h = ch + (r * (_op.nn.dense(H_t, rh)))
-                else:
-                    h = ch + _op.nn.dense((r * H_t), rh)
-
-            z = f_act(z)
-            r = f_act(r)
-            h = g_act(h)
-
-            H_t = ((_expr.const(1, dtype=W_dtype) - z) * h) + (z * H_t)
-            h_list.append(_op.expand_dims(H_t, axis=0))
+        Bidirectional GRU cell
+        """
+        seq_len = len(input_seqs)
+        forward_outputs, fw_H_t = gru_cell(
+            input_seqs,
+            **weight_dicts[0],
+            rz_act=acts[0],
+            n_act=acts[1],
+        )
 
-        if backwards:
-            # Canonical view is hidden states from the first token not last
-            h_list = h_list[::-1]
+        reverse_outputs, rev_H_t = gru_cell(
+            input_seqs,
+            **weight_dicts[1],
+            rz_act=acts[2],
+            n_act=acts[3],
+            backwards=True,
+        )
 
-        # Concatenate outputs and add back in direction axis.
-        concatenated = _op.concatenate(h_list, 0)
-        output = _op.expand_dims(concatenated, axis=1)
-        H_t = _op.expand_dims(H_t, axis=0)
+        final_outputs = []
+        for i in range(seq_len):
+            final_outputs.append(
+                _op.stack([forward_outputs[i], reverse_outputs[seq_len - 1 - i]], axis=0)
+            )
 
-        return output, H_t
+        return (
+            _op.stack(final_outputs, axis=0),
+            _op.stack([fw_H_t, rev_H_t], axis=0),
+        )
 
     @classmethod
     def _impl_v7(cls, inputs, attr, params):
@@ -2416,20 +2402,14 @@ def _impl_v7(cls, inputs, attr, params):
         W_dtype = infer_type(Wp).checked_type.dtype
 
         if num_directions not in [1, 2]:
-            raise NotImplementedError(
-                f"Directions for GRUs should be either 1 or 2 got {num_directions}"
-            )
+            raise ValueError("num_directions must be either 1 or 2!")
 
         X_shape = infer_shape(X)
         hidden_size = infer_shape(Rp)[-1]
         batch_size = X_shape[1]
 
-        # Initialize state if not provided.
-        # Otherwise remove bidirectional axis.
         if Hp_0 is None:
             Hp_0 = _op.zeros((num_directions, batch_size, hidden_size), W_dtype)
-        if Bp is None:
-            Bp = _op.zeros((num_directions, hidden_size * 6), W_dtype)
 
         if "activations" in attr:
             activations = attr["activations"]
@@ -2460,39 +2440,54 @@ def _impl_v7(cls, inputs, attr, params):
         else:
             acts = [_op.sigmoid, _op.tanh] * 2
 
-        result_output = []
-        result_H = []
+        # TODO (vvchernov): It can be replaced by _op.split if issue #8412 is resolved
+        X_steps = unbind(X, axis=0)
 
-        X_steps = _op.split(X, indices_or_sections=X_shape[0], axis=0)
         H_ts = _op.split(Hp_0, num_directions)
         Ws = _op.split(Wp, num_directions)
         Rs = _op.split(Rp, num_directions)
-        Bs = _op.split(Bp, num_directions)
 
+        if Bp is not None:
+            Bs = _op.split(Bp, num_directions)
+
+        weights_dicts = []
         for i in range(num_directions):
-            H_t = _op.squeeze(H_ts[i], axis=[0])
-            W = _op.squeeze(Ws[i], axis=[0])
-            R = _op.squeeze(Rs[i], axis=[0])
-            B = _op.squeeze(Bs[i], axis=[0])
-            f_act, g_act = acts[i * 2 : (i + 1) * 2]
-            output, H = GRU.generate_gru(
-                X_steps=X_steps,
-                H_t=H_t,
-                W=W,
-                R=R,
-                B=B,
-                linear_before_reset=linear_before_reset,
-                f_act=f_act,
-                g_act=g_act,
-                W_dtype=W_dtype,
-                backwards=i == 1,
-            )
+            weights_dict = {}
+
+            weights_dict["hidden_state"] = _op.squeeze(H_ts[i], axis=[0])
+            weights_dict["linear_before_reset"] = linear_before_reset
+
+            # Weights permutation: onnx format i-o-f-c, lstm cell format i-f-c-o
+            matz, matr, matn = _op.split(_op.squeeze(Ws[i], axis=[0]), 3)
+            weights_dict["w_inp"] = _op.concatenate([matr, matz, matn], axis=0)
+            matz, matr, matn = _op.split(_op.squeeze(Rs[i], axis=[0]), 3)
+            weights_dict["w_hid"] = _op.concatenate([matr, matz, matn], axis=0)
+            if Bp is not None:
+                Bi, Bh = _op.split(Bs[i], 2, -1)
+                matz, matr, matn = _op.split(_op.squeeze(Bi, axis=[0]), 3)
+                weights_dict["b_inp"] = _op.concatenate([matr, matz, matn], axis=0)
+                matz, matr, matn = _op.split(_op.squeeze(Bh, axis=[0]), 3)
+                weights_dict["b_hid"] = _op.concatenate([matr, matz, matn], axis=0)
+            weights_dicts.append(weights_dict)
 
-            result_output.append(output)
-            result_H.append(H)
+        if num_directions == 2:
+            output, H = GRU.bidir_gru_cell(
+                input_seqs=X_steps,
+                weight_dicts=weights_dicts,
+                acts=acts,
+            )
+        else:
+            # outputs shape = [seqs_num, (batch_size, hidden_size)]
+            outputs, H = gru_cell(
+                input_seqs=X_steps,
+                **weights_dicts[0],
+                rz_act=acts[0],
+                n_act=acts[1],
+            )
 
-        output = _op.concatenate(result_output, axis=1)
-        H = _op.concatenate(result_H, axis=0)
+            # output shape = (seqs_num, num_directions, batch_size, hidden_size)
+            output = _op.expand_dims(_op.stack(outputs, axis=0), axis=1)
+            H = _op.expand_dims(H, axis=0)
 
         return _expr.TupleWrapper(_expr.Tuple((output, H)), 2)