On 3 March 2018 at 21:26, Dibyendu Majumdar <mobile@xxxxxxxxxxxxxxx> wrote:
> On 13 November 2017 at 15:28, Christopher Li <sparse@xxxxxxxxxxx> wrote:
>> Currently value pseudo does not have size.
>> This create a problem pointed out by Dibyendu.
>> When using LLVM, calling varidic function with
>> constant value, there is no where to find the
>> size.
>>
>> Linus give out two suggestions. One is give pseudo
>> a size. The other one is the push instruction.
>> This is the implementation of the first suggestion.
>>
>> The model is actual very simple. The pseudo is
>> exactly as before if you are not looking at the size.
>> There is a size at create time, which tag alone with
>> it.
>>
>
> Chris, I think the discussion of this topic should be moved to this thread.
>
> I found a problem with this as I mentioned in the other thread. Last
> year a change was introduced to initialize aggregate structures in
> Sparse using a store instruction that uses a PSEUDO_VAL. However when
> this creates a pseudo the size is set to the size of the aggregate
> types - and this size (> 64 bits) is kind of nonsensical for a
> PSEUDO_VAL.
>
> I suggested that when creating a PSEUDO_VAL we should only create
> distinct values when size is register size - i.e. one of 8, 16, 32, or
> 64. Else we should set size to 0.
>
> Couple of more points:
>
> a) We should also set size to 0 when we create a PSEUDO_VAL in CSE for
> uninitialized vars.
> b) We should ideally avoid CSE on PSEUDO_VAL with size = 0 because I
> don't think it makes sense to do so - i.e. they either represent
> uninitialized vars or aggregates > 64 bits.
>
> The above aggregate initialization change is one of the changes I did
> not merge into my project as I wasn't happy with it. I still think
> this change is not correct and needs to be removed or redone. I am not
> 100% sure but presumably creating PSEUDO_VAL where the instruction
> size is > 64-bits means that these PSEUDO_VAL values might be
> considered 'same as' any other PSEUDO_VAL with value 0.
>
Forgot to add a simple example from my test pack:
struct foo {
long long int i,j;
};
extern void dosomething(struct foo *foo);
int main(void)
{
struct foo bar = { 99 };
dosomething(&bar);
return 0;
}
Here you will see a PESUDO_VAL with value 0 being created with size 16 bytes.
Regards
--
To unsubscribe from this list: send the line "unsubscribe linux-sparse" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
