[PATCH] D77868: [InstSimplify] fold select of bools using bitwise logic

[Juneyoung Lee via Phabricator via llvm-commits]

aqjune added a comment.

Maybe I can write a simple version of `bool isPoisonIf(Value *X, Value *PoisonAssumedVal)` into ValueTracking which returns true if `X` is poison, given that `PoisonAssumedVal` is already poison.
Then, the optimizing part can be rewritten as:

  // select Cond, T, false --> Cond & T
  if (match(F, m_ZeroInt()) && isPoisonIf(Cond, T))
    return SimplifyAndInst(Cond, T, Q);

This will also support folding `select (icmp X, C1), (icmp X, C2), false`, because `(icmp X, C1)` is poison if `(icmp X, C2)` was poison.


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  https://reviews.llvm.org/D77868/new/

https://reviews.llvm.org/D77868