[PATCH] D125248: [instcombine] Propagate freeze back to def

[Nikita Popov via Phabricator via llvm-commits]

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I don't think this is the right place to do this. You should either:

1. Remove the one-use restriction on this fold, and replace other uses with the frozen variant as well. This is on the premise that pushing freeze higher is more worthwhile than having some un-frozen uses.

2. Adjust the freezeDominatedUses() fold to freeze not only dominated uses. Basically canonicalize %x to freeze %x. This is on the premise that allowing more exploitation of value identity is more worthwhile than having un-frozen uses.

I'm not sure which one of these is the right approach, and I didn't really understand what optimization is supposed to be achieved in your example -- you might want to construct it in a way that something actually folds away as a result.


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https://reviews.llvm.org/D125248