[llvm-dev] RFC: Killing undef and spreading poison

[Nuno Lopes via llvm-dev]

> Ok, freeze() produces a fixed but undefined value, so that xor'ing the same frozen value produces 0, ANDing a frozen value with 1 produces known zero bits everywhere except the LSB, which is undefined.
> 
> Does every instance of freeze() produce a *different* fixed but undefined value? i.e. the value produced by freeze() is labelled with a sequence number or something like that?

Freeze produces an arbitrary value.  The compiler is free to pick a "good" one (one that enables some optimization) if it wishes so.  There's no determination of these values.
It's similar to current undef, except that all uses see the same value.

Nuno