[PATCH] D15232: [InstCombine] Aggressively fold compares that can be discovered to be constant

[Philip Reames via llvm-commits]

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At a high level, I'm a bit unsure about the formulation chosen here.  I'm worried that seeking to find a set of constant values through a potentially large value graph might be expensive.

A couple of specific questions:

- The examples you've listed should be entirely handled by LazyValueInfo and either JumpThreading or CVP.  Do you have a strong reason InstCombine needs to perform the same optimization?
- Have you considered phrasing this as pushing the query (i.e. icmp) back along the inputs?  Doing this might a) let you terminate earlier or b) unswitch the comparison if the select is only used by the compare.


http://reviews.llvm.org/D15232