llvm dev - Apr 2016 - Different index types in GEPs -> non-aliasing?

Hi,

On 04/18/2016 05:28 PM, Vedant Kumar wrote:
> This sounds like a bug to me.
>
>
>>   // If the last (struct) indices are constants and are equal, the
other indices
>>   // might be also be dynamically equal, so the GEPs can alias.
>>   if (C1 && C2 && C1 == C2)
>>     return MayAlias;
>
> Does changing this condition fix the issue? E.g
>
>    if (C1 && C2 && C1->getSExtValue() ==
C2->getSExtValue()) { ... }
Yes it does. Then it realize the two GEPs alias and I get the expected 
result.

But since there is also a Value pointer comparison in

bool BasicAAResult::isValueEqualInPotentialCycles(const Value *V,
                                                   const Value *V2) {
   if (V != V2)
     return false;

and probably in several other places too I wasn't comfortable just 
changing it... Right now I made my front-end always use i64 for GEP 
array indices instead.

Should I file a bugzilla report on this?

Regards,
Mikael
>
>
> best
> vedant
>

> On Apr 18, 2016, at 10:55 PM, Mikael Holmén <mikael.holmen at
ericsson.com> wrote:
> 
> Hi,
> 
> On 04/18/2016 05:28 PM, Vedant Kumar wrote:
>> This sounds like a bug to me.
>> 
>> 
>>>  // If the last (struct) indices are constants and are equal, the
other indices
>>>  // might be also be dynamically equal, so the GEPs can alias.
>>>  if (C1 && C2 && C1 == C2)
>>>    return MayAlias;
>> 
>> Does changing this condition fix the issue? E.g
>> 
>>   if (C1 && C2 && C1->getSExtValue() ==
C2->getSExtValue()) { ... }
> 
> Yes it does. Then it realize the two GEPs alias and I get the expected
result.
> 
> But since there is also a Value pointer comparison in
> 
> bool BasicAAResult::isValueEqualInPotentialCycles(const Value *V,
>                                                  const Value *V2) {
>  if (V != V2)
>    return false;
> 
> and probably in several other places too I wasn't comfortable just
changing it... Right now I made my front-end always use i64 for GEP array
indices instead.
Yes, I think it'd be best to open up a bug for this.

thanks
vedant

> Should I file a bugzilla report on this?
> 
> Regards,
> Mikael
> 
>> 
>> 
>> best
>> vedant
>>

Hi,
On 04/19/2016 07:59 AM, Vedant Kumar wrote:
>
> [...]
>
> Yes, I think it'd be best to open up a bug for this.
>
> thanks
> vedant
Alright, here it is

https://llvm.org/bugs/show_bug.cgi?id=27418

Regards,
Mikael