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

[John Regehr via llvm-dev]

As I understand (others have better thoughts on this than I do) it is 
difficult to make the "definitely not poison" analysis return useful 
answers very much of the time.  Instead, we try to write transformations 
that work regardless of whether a value is poisoned.

John


On 6/16/17 9:41 AM, Krzysztof Parzyszek via llvm-dev wrote:
> On 6/16/2017 10:36 AM, Krzysztof Parzyszek via llvm-dev wrote:
>> On 6/16/2017 10:01 AM, Peter Lawrence via llvm-dev wrote:
>>> “Poison” is an attribute of a “value”, not a “value” itself.
>>>
>>> “Poison” is an analysis result, and we should think about
>>> implementing it as such,
>>> just like we do constant and range analysis.
>>
>> Why do you insist on treating it as an attribute? It's more like NaN
>> for floating point: "not a value".
>
> I'm guessing here---are you thinking of "could-be-poison" as opposed to
> "is-poison"?
>
> -Krzysztof
>