[PATCH] D61314: [SCCP] Remove forcedconstant, go to overdefined instead

[Eli Friedman via Phabricator via llvm-commits]

efriedma added a comment.

Adding an explicit "undef" lattice state makes sense, I think; it should allow modeling everything we need correctly.

> Also, from the comments in ValueLattice.h and in LVI, it seems the code expects unknown to mean unreachable/dead, which is slightly different to undef and the new state would help to clarify this.

Yes, I'm happier reserving unknown for unvisited values.  It wouldn't be too much of a stretch to also use it for poison values, since they have similar properties in terms of the lattice.  (Granted, we don't try to model poison in SCCP at the moment.)


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

https://reviews.llvm.org/D61314