[LLVMdev] RFC: Proposal for Poison Semantics

[Chandler Carruth]

On Tue, Jan 27, 2015 at 6:50 PM, David Majnemer <david.majnemer at gmail.com>
wrote:

> Examples of this rule which do not result in poison:
> ```
>   %or  = or  i32 %always_poison, 2
>   %and = and i32 %always_poison, 2
>   %mul = mul i32 %always_poison, 0
> ```
>
> In fact, it would be reasonable to optimize `%or` to `2` and `%and` to
> `0`.  In this respect, poison is not different from `undef`.
>

The last time we discussed this, we were considering poison a property of
an individual bit much like undef is a property of an indivdual bit. Are
you no longer proposing those semantics? That is, while %or's second bit is
clearly not poison, is the first bit (or LSB) poison?
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