[RFC] split the `tensor` dialect from `std`

MLIR
16

Finally got back to this after the holiday break. I managed to move all the ops (one patch still in flight) except for std.subtensor (and std.subtensor_insert, which I’m choosing to keep with it). std.subtensor has a bunch of common helper code with the std.subview op, and that common code relies on being able to create an std.constant of index type.

  • std.subtensor and std.subview depend on common code, which relies on std.constant 1
  • currently, std dialect depends on tensor (for example, some std ops have canonicalization patterns that use tensor ops)

Thus, putting std.subtensor into the tensor dialect would create a circular dependency.

So that means that we need to wait on defragging std.constant. The minimal change here would be to create an int dialect and have int.constant there that excises the int part of std.constant.