llvm dev - Jul 2017 - LazyValueInfo vs ScalarEvolution

On Mon, Jul 24, 2017 at 2:29 PM, John Regehr via llvm-dev <
llvm-dev at lists.llvm.org> wrote:
> On 7/24/17 3:16 PM, Hongbin Zheng via llvm-dev wrote:
>
>> Thanks, maybe we could use ScalarEvolution in LazyValueInfo if it is
>> available?
>>
>
> This should be fairly easy to try, if you want to propose a patch and run
> some experiments. The question is whether the benefit in terms of improved
> optimization power is worth the compile-time cost.
 Ok

Also, the last time I looked, there seemed to be a fair amount of room
for
> improvement in LVI and ConstantRange.
Could you point some out?


Thanks
Hongbin
>
>
> John
>
>
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On 07/24/2017 03:43 PM, Hongbin Zheng wrote:
>     Also, the last time I looked, there seemed to be a fair amount of
>     room for improvement in LVI and ConstantRange.
> 
> Could you point some out?
Check out the TODO items in binaryAnd and BinaryOr in ConstantRange.cpp.

There are some missing cases in the switch in ConstantRange::binaryOp, 
such as xor and ashr.

Argh this is embarrassing, I have some unfinished work sitting in 
Phabricator that could use a helper if you have time to take a look:

https://reviews.llvm.org/D19859
https://reviews.llvm.org/D20669
https://reviews.llvm.org/D19867
https://reviews.llvm.org/D19559

John

Also I should add that I strongly doubt that it will be acceptable to 
simply call ScalarEvolution's integer range analysis from LVI. The right 
answer is no doubt more nuanced and the actual experts in this stuff are 
here and hopefully they can chime in with opinions. Also, I am hoping to 
get together with a few people who care about LVI at the October dev 
meeting, you should join if you are going to attend.

John


On 07/24/2017 03:59 PM, John Regehr wrote:
> On 07/24/2017 03:43 PM, Hongbin Zheng wrote:
>>     Also, the last time I looked, there seemed to be a fair amount of
>>     room for improvement in LVI and ConstantRange.
>>
>> Could you point some out?
> 
> Check out the TODO items in binaryAnd and BinaryOr in ConstantRange.cpp.
> 
> There are some missing cases in the switch in ConstantRange::binaryOp, 
> such as xor and ashr.
> 
> Argh this is embarrassing, I have some unfinished work sitting in 
> Phabricator that could use a helper if you have time to take a look:
> 
> https://reviews.llvm.org/D19859
> https://reviews.llvm.org/D20669
> https://reviews.llvm.org/D19867
> https://reviews.llvm.org/D19559
> 
> John
>