[Feature Request] Add shape checking to Placeholder Tensors

[mbartling]

Right now there is no shape checking on Placeholder tensors, this means that invalid shapes will still propagate through the model and lead to weird errors.

[neil-tan]

@mbartling Your point is valid. This relates to a trade-off between runtime's simplicity and code-gen's complexity. Perhaps, a middle ground would be using C++'s #ifdef macro, including checking, testing and profiling code only when needed?

[mbartling]

@neil-tan I completely disagree. This is 100% a runtime issue only and should not be pushed into codegen.

It is a single if case.

[janjongboom]

+1000