[llvm-dev] a tagged architecture, the elephant in the undef / poison room

[Matthias Braun via llvm-dev]

> On Jun 16, 2017, at 12:31 PM, John Regehr via llvm-dev <llvm-dev at lists.llvm.org> wrote:
> 
>> Only freezing it will
>> replace it with something concrete such that if x is poison then
>> freeze(x) == freeze(x), etc.
> 
> Nit: it's not true that freeze(x) == freeze(x) in the current proposal. Each freeze can choose its own value.
Just for my understanding: Freeze is an instruction isn't it? So this example has to read either:

%a = freeze(poison)
%b = freeze(poison)
%cond = icmp eq %a, %b

then %cond isn't necessarily true (and also not necessarily false).

While:

%a = freeze(poison)
%cond = icmp eq %a, %a

is always true. Right?

- Matthias