[llvm-dev] loop canonical variables

[Sanjoy Das via llvm-dev]

Hi Anastasiya,

If it fits you use case, you can consider walking the loop header and
calling getSCEV() on all of the PHI nodes in the header.  This will
give you a SCEV* which should be easier to analyze than manually
inspecting PHI cycles.

Thanks!
-- Sanjoy


On Tue, Jul 25, 2017 at 11:42 AM, Michael Kruse via llvm-dev
<llvm-dev at lists.llvm.org> wrote:
> 2017-07-25 19:32 GMT+02:00 Anastasiya Ruzhanskaya
> <anastasiya.ruzhanskaya at frtk.ru>:
>> I call this function and it returns only "i" in my example.  Are there any
>> ways to return "j" also?
>
> That would contradict it being the /canonical/ induction variable, wouldn't it?
>
> If you look into the imlplementation of
> getCanonicalInductionVariable(), it just walks the IR instructions and
> checks some conditions. You can have your own implementation that,
> instead of returning the first matching PHI, return all matching PHIs.
> SimplifyIndVar won't try to canonicalize, though.
>
> Michael
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