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

Fri Mar 27 11:28:35 PDT 2020

fhahn added a comment.

In D76931#1946483 <https://reviews.llvm.org/D76931#1946483>, @aqjune wrote:

> Hi,
>  The semantics of whether br undef is nondet. choice or UB really has been a topic between me and Nuno too.
>  As @nikic said, we can define it as UB if which branch to take depends on an undef value.

Yes, the example in the description is just the tip of the iceberg. If branch on undef would not be UB, there are many more cases that CVP would miss I think, unless we teach it to insert freeze I guess

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https://reviews.llvm.org/D76931