[PATCH] D65148: [SimplifyCFG] Bump phi-node-folding-threshold from 2 to 3

[Roman Lebedev via Phabricator via llvm-commits]

lebedev.ri added a comment.

In D65148#1624762 <https://reviews.llvm.org/D65148#1624762>, @craig.topper wrote:

> Did anything happen with the extractvalue cost suggestion?


I was planning to look into that, and i just did. Some observations:

1. I'm not sure we can literally treat any `extractvalue` as free, it clearly isn't: https://godbolt.org/z/6wIxAa
2. Even if we do treat it as free in `TargetTransformInfo::getInstructionThroughput()`, it is not sufficient yet to get the fold
3. We also need to do the same in `TargetTransformInfoImplCRTPBase::getUserCost()` because again, `PHINodeFoldingThreshold` is at `2`.
4. While that addresses the `unsigned-multiply-overflow-check.ll`, it still leaves `signbit-like-value-extension.ll` on the table.


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  https://reviews.llvm.org/D65148/new/

https://reviews.llvm.org/D65148