[llvm-dev] Infinite loops with no side effects

[Reid Kleckner via llvm-dev]

On Fri, Oct 27, 2017 at 1:08 PM, Hal Finkel <hfinkel at anl.gov> wrote:

> On 10/27/2017 02:51 PM, Reid Kleckner wrote:
>
> Personally, I don't like the side effect intrinsic.
>
>
> Understood. I also don't like the fact that it will clutter the IR in many
> cases.
>
> It will pollute all the IR generated by non-C frontends. What most of
> these frontends really want is just a switch to disable a targeted set of
> optimizations.
>
> One thing I like about the function attribute idea is that it's
> conservatively correct to discard it when doing cross-language inlining. It
> just becomes something that C-family frontends need to remember to add to
> enable their special-case language rules, rather than something that non-C
> languages need to think about. Similar to the 'access', builtin vs
> nonbuiltin discussion happening in parallel, the attribute enables the
> optimization, rather than inhibiting it.
>
>
> As I said below, a function attribute is insufficient. It needs to be
> something we can mark per loop. This is needed to correctly model C. The
> sideeffect intrinsic is the best proposal I've seen so far.
>

Maybe we should do both? If the intrinsic is a special case, that seems
fine. It's cheap.
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