[llvm-commits] [PATCH] treat calls to noreturn functions as side effecting

[Duncan Sands]

Hi Chandler,

> Anyways, LLVM, much to my regret, decided to make infinite loops a magical
> observable side-effect, and not delete them. One of the consequences of this
> decision is that there is one of two bugs in the current system now:
>
> 1) functionattrs shouldn't mark functions with infinite loops as readonly, or
> 2) noreturn functions should have the same "observable" property as infinite loops.
>
> As there are many noreturn functions which do not have infinite loops and to
> which this magical property really shouldn't apply, I strongly prefer #1. It
> also clarifies the cost of this treatment of infinite loops -- they are
> implicitly a side-effect carrying construct.
>
> So in essence, I think this is a bug in functionattrs which stems from the
> decision to not delete infinite loops.

I disagree.  Read-only is what it says: the function only reads memory, doesn't
write it.  What has that to do with infinite loops?  I would rather see another
attribute, call it "finite", for functions that can be proved to complete in
finite time.  Then a function call with no uses can be deleted if read-only,
nounwind and finite.

Ciao, Duncan.