This patch adds an option to select the method for computing complex
number division. It uses `LoweringOptions` to determine whether to lower
complex division to a runtime function call or to MLIR's `complex.div`,
and `CodeGenOptions` to select the computation algorithm for
`complex.div`. The available option values and their corresponding
algorithms are as follows:
- `full`: Lower to a runtime function call. (Default behavior)
- `improved`: Lower to `complex.div` and expand to Smith's algorithm.
- `basic`: Lower to `complex.div` and expand to the algebraic algorithm.
See also the discussion in the following discourse post:
https://discourse.llvm.org/t/optimization-of-complex-number-division/83468
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Co-authored-by: Tarun Prabhu <tarunprabhu@gmail.com>
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