[PATCH] D76931: [ValueLattice] Distinguish between constant ranges with/without undef.

Sat Mar 28 00:30:34 PDT 2020

aqjune added a comment.

In D76931#1946577 <https://reviews.llvm.org/D76931#1946577>, @efriedma wrote:

> Ultimately, I'm think trying to redefine undef at this point would act as a distraction for the poison work.  That seems worse than whatever minor improvement we might get from redefining it.

I agree, but removing undef value seems to be a pretty big work. Before that happens, making existing optimizations work consistently w.r.t undef might be an important job.

I made a LangRef change patch to make the semantics of branching on undef explicit here: https://reviews.llvm.org/D76973

Repository:
  rG LLVM Github Monorepo

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https://reviews.llvm.org/D76931