The quantum-opt build target provides a general IR processing & debugging tool.
The most basic way to process IR is to test whether it can be parsed and re-emitted correctly in a process called "round-tripping".
This will guarantee that the textual format is syntactically correct and can be converted to and from its in-memory representation, as well as that all IR invariants are satisfied by the input.
To do so, run the tool on an .mlir input file or stdin via quantum-opt <input>.
More importantly, the opt tool can be used to transform IR via compiler passes defined in lib/Transforms.
In general, passes can be arbitrarily combined to form a pass pipeline via a quantum-opt -<pass1> -<pass2> ..., typically with the goal to optimize a program and/or transform it a lower level of abstraction.
Certain passes, however, may only make sense under a certain (partial) ordering.
The following passes are available on quantum programs (in addition to all standard MLIR passes, see quantum-opt -h for the full list):
-convert-mem-to-val: Convert quantum operations from memory to value semantics.-quantum-gate-opt: Run a variety of quantum optimization patterns using the greedy pattern rewrite driver.-circuit-inline: Inline circuit calls.-count-resources: Remove all quantum operations from the program & count quantum resources instead.-strip-circ: Remove unused circuit definitions.-lower-ctrl: Lower controlled circuit calls by propagating the control modifier into the function body.