[llvm-dev] RFC: inbounds on getelementptr indices for global splitting

Peter Collingbourne via llvm-dev llvm-dev at lists.llvm.org
Mon Jul 25 17:51:24 PDT 2016

Thanks Tobias. I've sent https://reviews.llvm.org/D22793 which implements
this IR extension, and updated D22295 to use the extension.


On Tue, Jul 19, 2016 at 10:55 PM, Tobias Grosser <tobias at grosser.es> wrote:

> On Tue, Jul 19, 2016, at 03:02 AM, Peter Collingbourne via llvm-dev
> wrote:
> > Hi all,
> >
> > I'd like to propose an IR extension that allows the inbounds keyword to
> > be
> > attached to indices in a getelementptr constantexpr.
> Hi Peter,
> this proposal (in its updated version with load/stores triggering the
> undef) is a good idea. It will also help to propagate out-of-bounds
> information from C to LLVM-IR, which we are currently lacking at IR
> level. As a result, multi-dimensional data-dependence analysis must
> either take possible out-of-bounds accesses into consideration or emit
> run-time checks to be correct. In Polly we have already been considering
> to pass the information provided by your inbounds keywords  using
> llvm.assume [1], to avoid this additional complexity. However,  as this
> is littering the IR with assumptions, the relevant patch  was never
> proposed for integration. Your approach is well targeted and  due to the
> additional use cases you mention especially appealing.
> Best,
> Tobias
> [1] https://llvm.org/bugs/show_bug.cgi?id=27067

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