[PATCH] SelectionDAG: fold (fp_to_u/sint (u/sint_to_fp val)) when possible

[Fiona Glaser]

Okay, I’ve implemented a cleaner and nicer InstCombine per suggestions.

The two things I remain unsure about:

1) is the use of replacealluseswith correct? Should I be using it elsewhere?

2) should the DAG combine be enhanced too to match the InstCombine? That is, are we allowed to take advantage of undefined behavior in the DAGCombine, or is that bad because the target may shuffle around the DAG in ways that relies on target-specific behavior?

Fiona

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