[PATCH] D75120: [ValueLattice] Add new state for undef constants. (WIP)

[Eli Friedman via Phabricator via llvm-commits]

efriedma added a comment.

If you don't have all the relevant states represented in the ValueLattice, where are you storing the "possibly undef" bit?  I think having all the states in the ValueLattice is simpler, at least conceptually.



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Comment at: llvm/lib/Transforms/Scalar/SCCP.cpp:439
-      // Undef values remain unknown.
-      if (!isa<UndefValue>(V))
         LV.markConstant(C);          // Constants are constant
----------------
fhahn wrote:
> efriedma wrote:
> > Not sure about this change; do we not need to markUndef?
> markConstant used to be a no-op for UndefValue constants. I've updated it to use markUndefined for UndefValue constants, it might be clearer to do it explicitly here though?
Oh, right, that makes sense.


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  https://reviews.llvm.org/D75120/new/

https://reviews.llvm.org/D75120