[flang-commits] [flang] [flang] Allow lowering of sub-expressions to be overridden (PR #69944)

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jeanPerier wrote:

> The only question I have is whether this addition of state to expression lowering will make any future parallel lowering of expressions impossible.

Thanks for the review. Yes, this change does not help, but expression lowering is already depending on the converter state since it is providing the symbol map (at least when expression lowering is called via the converter).

We would first need to define the lowering parallelism requirements here. Is to lower expressions of a single statement in parallel, or is it to allow different program units to be lowered in parallel? The former seems hard and of little practicality to me. The latter makes more sense, and then, I think we could modify the bridge a bit in order to have a "converter" instance per thread/program unit lowering, in which case this change is not a blocker (sub-expression override would only impact a single thread/program unit lowering).

https://github.com/llvm/llvm-project/pull/69944