[llvm-dev] PHI nodes and connected ICMp

Anastasiya Ruzhanskaya via llvm-dev
Sun, 13 Aug 2017 12:58:21 -0000

And still, aren't there any possibilities to find that phi node, that led
SCEV to compute max trip count?

2017-08-13 14:55 GMT+02:00 Anastasiya Ruzhanskaya <
anastasiya.ruzhanskaya at frtk.ru>:

> To continue this topic:
> sometimes SCEV's behavior is rather controversial : for loops with i
> changing as i \=2 for example, he can't figure what the type of
expressions
> is, but surprisingly can determine max trip count. Shouldn't it be able
to
> detect or not detect  these parameters at the same time?
>
> 2017-08-11 15:56 GMT+02:00 Anastasiya Ruzhanskaya <
> anastasiya.ruzhanskaya at frtk.ru>:
>
>> Sorry,  I just saw this enumeration with SCEV types - all operations
>> should be possible then...
>>
>> 2017-08-11 15:55 GMT+02:00 Anastasiya Ruzhanskaya <
>> anastasiya.ruzhanskaya at frtk.ru>:
>>
>>> Thank you for your answer! I tested your example, yes, perhaps I
should
>>> preserve some kind of tree to parse this start and end expressions
for
>>> induction variable... I was surprised, that SCEV cannot compute the
>>> tripcount here. I thought, that all linear and maybe expressions
with
>>> multiplication are suitable for analysis.
>>>
>>> 2017-08-10 19:30 GMT+02:00 Sanjoy Das <sanjoy at google.com>:
>>>
>>>> Hi Anastasiya,
>>>>
>>>> If you're looking for the exit value of a PHI node, please
take a look
>>>> at what IndVarSimplify does here:
>>>> https://github.com/llvm-mirror/llvm/blob/master/lib/Transfor
>>>> ms/Scalar/IndVarSimplify.cpp#L516
>>>>
>>>> On Thu, Aug 10, 2017 at 12:55 AM, Anastasiya Ruzhanskaya
>>>> <anastasiya.ruzhanskaya at frtk.ru> wrote:
>>>> > By only two cases I mean , that in exiting block when
computing the
>>>> > condition related to PHI node I can expect only icmp on
one of
>>>> incoming
>>>> > values or on phi node itself... I tried to come up with
some more
>>>> complex
>>>> > examples but I always receive only these two cases, that
is why I am
>>>> asking.
>>>>
>>>> So you could have cases like this: https://godbolt.org/g/j4zcWy
>>>>
>>>> -- Sanjoy
>>>>
>>>
>>>
>>
>
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