[PATCH] D23214: [AliasAnalysis] Treat invariant.start as read-memory

[Daniel Berlin via llvm-commits]

LGTM.
Thank you

On Tue, Aug 9, 2016 at 9:59 AM, Anna Thomas <anna at azul.com> wrote:

> anna marked 2 inline comments as done.
>
> ================
> Comment at: lib/Analysis/BasicAliasAnalysis.cpp:785
> @@ +784,3 @@
> +  // Like assumes, invariant.start intrinsics are also marked as
> arbitrarily
> +  // writing so that proper control dependencies are maintained but they
> never
> +  // mod any particular memory location visible to the IR.
> ----------------
> anna wrote:
> > dberlin wrote:
> > > Errr, this is now wrong?
> > >
> > > Maybe you mean "were both also marked"?
> > I'm not sure if the comment is wrong. The comment intended to convey:
> "In other code such as MDA, instruction->MayWriteToMemory, etc, assumes and
> invariant.start are marked as read/write, even though they do not modify
> memory" However, while assume is marked as NoModRef above, we need to mark
> invariant.start as reading memory.
> >
> > It actually follows from the above 2 intrinsic comments "assume and
> experimental_guard" :)
> > Should I update the comment?
> >
> I've updated the comment to:
> Like assumes, invariant.start intrinsics were also marked as arbitrarily
> writing so that proper control dependencies are maintained but they never
> mod any particular memory location visible to the IR.
> *Unlike* assumes (which are now modeled as NoModRef), invariant.start
> intrinsic is now modeled as reading memory. This prevents hoisting the
> invariant.start intrinsic over stores.
>
>
> https://reviews.llvm.org/D23214
>
>
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20160809/fa45bd6c/attachment.html>