[LLVMdev] BasicAA unable to analyze recursive PHI nodes

Daniel Berlin
Wed, 10 Jun 2015 22:44:41 -0000

What is the compile time impact?  Basic AA is supposed to be basic, not
catch every case

On Wed, Jun 10, 2015, 3:33 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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