Are you aware of any document (preferably academic paper) describing TableGen's typing of the following fields used to describe Instruction: pattern, ins and outs.
I found a few pages on TableGen, but none of them talking about these fields:
Although not (really) about TableGen, I found a good paper talking about the instruction selection in LLVM: http://llvm.org/pubs/2008-CGO-DagISel.pdf .
Both "ins" and "outs" are DAGs (in tablegen's terminology). These are lists of inputs and outputs with specific types or with register classes assigned to them. The patterns are also DAGs, but more complex. Each node in the DAG has a set of types associated with it (from the source representation in the .td file) and those sets are then reduced to match the constraints from the instructions (i.e. the ins and outs), SDTypeConstraints, etc. At the end, a matching code is generated that enforces the required types for each tree node.
I am not aware of any academic paper about it. The type system used in tablegen is not overly complicated. Most of it is implemented in utils/TableGen/CodeGenDAGPatterns.cpp.