Codegen for the MLIR backend

[tmarzec]

This PR contains an implementation for MLIR codegen using the new sdql dialect in scair (see edin-dal/scair#391).

How to emit the MLIR code

Usage: run to_mlir <path> <sdql_file>
Example: run to_mlir progs/tpch q6.sdql

TPC-H coverage

Codegen succeeds for 19/22 queries. Current failures: q4, q15, and q22.

MLIR code for queries can be generated using gen_tpch_mlir.sh
Example: ./gen_tpch_mlir.sh /tmp/tpch-queries-mlir

Known limitations

• Untyped empty dicts can break codegen when their type must be inferred. A fix is partially implemented (passing an “expected type” through function calls), but some edge cases remain.
• Some language features are not yet supported (e.g., Load.skipCols, DictNode.hint).
• The date type is lowered to i32. It should be investigated how it should be represented in MLIR.
• Local SSA/value name collisions can occur with certain bound variable names.