fix RNN and IfElse syntax in Block design

[Superjomn]

No description provided.

[emailweixu]

h is not defined

[emailweixu]

If the framework knows whether x contains instances, user does not indicate x as ifelse_input. The use can directly use x in the block and the framework can automatically do the splitting.

[Superjomn]

some x that has instances might not need to be split.

such as

# v is some op's output
v = some_op() # shape is [20, 20]
data = var(shape=[20, 20])

with ie.true_block():
    # split x
    x = data.as_ifelse_input() # shape [1, 20]
    # v should not be split
    y = pd.matmul(x.T, v) # shape [1, 20]
   y_T = y.T # [20, 1]
   ie.set_outputs(y_T)

v has the same batch_size, but do not need to be split.

if write as

with ie.true_block():
    y = pd.matmul(x, v) # shape [1, 20] x [1, 20] wrong

the shapes will not match.

[emailweixu]

If a variable has fixed size, it's not splittable. If a variable's size depends on batchsize, it must be splitted because it means that it contains data for each instances.

[Superjomn]

oh, I see, I will change this latter.

[wangkuiyi]

I have a replacement here #4313

[emailweixu]

RNN needs to differentiate static input and sequence input. Static input is same for every step. Sequence input will have to pick the corresponding data for each step. I suggest that static input uses same syntax as if-else, while sequence input needs to explicitly indicate it as step input (e.g., using as_step_input())

[wangkuiyi]

LGTM