[LLVMdev] BasicAA unable to analyze recursive PHI nodes

Tobias Edler von Koch
Wed, 10 Jun 2015 23:09:20 -0000

It probably will, but it isn't on by default (right?) and has quite a
lot more overhead. I think this is a common enough case for it to be
handled by BasicAA.

On Wed, 10 Jun 2015 15:52:07 -0700 Sanjoy Das
<sanjoy at playingwithpointers.com> wrote:

> Sorry for missing this the first time around, but I think -scev-aa
> does what you want.  I've commented on the phabricator review.
>
> On Wed, Jun 10, 2015 at 3:32 PM, Tobias Edler von Koch
> <tobias at codeaurora.org> wrote:
> > On Tue, 2 Jun 2015 11:32:13 -0500 Tobias Edler von Koch
> > <tobias at codeaurora.org> wrote:
> >
> >> Hi all,
> >>
> >> I came across the following limitation in our BasicAliasAnalysis.
This
> >> happens with the following IR pattern:
> >>
> >>   %x = phi [ %incptr, ... ] [ %var, ... ]
> >>   %incptr = getelementptr %x, 1
> >>
> >> We will basically always return MayAlias for %x and any other
value
> >> because aliasPHI recurses on the first value and gives up.
> >
> > Patch now posted as http://reviews.llvm.org/D10368
> >
> > Tobias
> >
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> > Linux Foundation Collaborative Project.
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