[llvm-dev] Is every intrinsic norecurse?

[Daniel Berlin via llvm-dev]

On Thu, Oct 19, 2017 at 10:23 PM, Mikael Holmén via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> Hi,
>
> Also, I think there is a bigger problem lurking than just with norecurse.

Yes


> I think that in general, functionattrs is not very good with attributes
> when intrinsics are present.
>


>
> E.g.
> https://bugs.llvm.org/show_bug.cgi?id=34696
>
> Here dbg.value prevents both norecurse and readnone from being deduced.
>

A lot of these are the more general issue of intrinsics not being marked
with proper memory attributes as a form of attempted control
dependence/optimization blocking/etc

Intrinsics.td even says this.


> So, it would be nice to fix this for norecurse, but it would be even nicer
> to fix it for intrinsics and attributes in general.
>

Nobody as of yet has signed up to fix this, because it often requires
significant thinking about each intrinsic and what really should be
happening to it, modeling that, and teaching optimizers to deal with it.

Instead the large hammer is chosen.

Eventually it'll matter enough to performance for someone to do the work :)
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