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

[Eli Friedman via Phabricator via llvm-commits]

efriedma added a comment.

I'm not quite sure the merge function here is right.  I think constant_merged_with_undef has to be a different state from constant.  It's basically the same as constant, except that merging it with a different constant or constantrange produces overdefined.



================
Comment at: llvm/lib/Transforms/Scalar/SCCP.cpp:439
-      // Undef values remain unknown.
-      if (!isa<UndefValue>(V))
         LV.markConstant(C);          // Constants are constant
----------------
Not sure about this change; do we not need to markUndef?


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

https://reviews.llvm.org/D75120