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

Matthias Braun via llvm-dev llvm-dev at lists.llvm.org
Fri Jun 16 13:05:13 PDT 2017

> 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).


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

is always true. Right?

- Matthias

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