[PATCH] D88687: [InstCombine] visitTrunc - pass through undefs for trunc(shift(trunc/ext(x),c)) patterns

[Roman Lebedev via Phabricator via llvm-commits]

lebedev.ri added a comment.

Instead of eventually potentially duplicating the entirety of `ConstantExpr` methods,
i wonder if we can get away with an inverse of `Constant::replaceUndefsWith()`,
that takes two constants, and does an element-wise or'ing of `undef`s,
i.e. the LHS constant gets all the additional undefs that the RHS constant has.


Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D88687/new/

https://reviews.llvm.org/D88687