[PATCH] D61314: [SCCP] Remove forcedconstant, use InstSimplify to fold undef values.

[Eli Friedman via Phabricator via llvm-commits]

efriedma added a comment.

Oh, hmm, in terms of optimization I guess you get some benefit from making assumptions about the behavior of undef, instead of only interacting with it through constant folding.  You get better results by implicitly unifying UndefValue with other constants in PHI nodes and call arguments, and forcing branches one way instead of both ways.  Maybe this is better than completely dropping ResolveUndefsIn.  Maybe this approach is fine, then.

I'd prefer to finish and land this first, and let it bake a little while, before landing the other pieces.  It seems a little riskier than the rest, since it's really hard to reason about undef-related changes.


Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D61314/new/

https://reviews.llvm.org/D61314