[PATCH] D20789: Consecutive memory access in Loop Vectorizer - fixed and simplified

[Adam Nemet via llvm-commits]

I am wondering if we have an off-by-one error with the bounds.  These casts look suspicious and I am wondering if we properly account for the entire object accessed in the last iteration.  Elena, is the overlap on the last element of the array or something?

> On Aug 2, 2016, at 11:16 AM, Demikhovsky, Elena <elena.demikhovsky at intel.com> wrote:
> 
> Right. As you see, the distance between %op and %src is not checked.
> %bound0 is some arithmetic between %op and %len
> And
> %bound1 is some arithmetic between %src and %len
> 
> The loop just for the reference:
>  while (len > 0) {
>      *(reinterpret_cast<long long*>(op)) = *(reinterpret_cast<const long long*>(src));
>        src += 8;
>        op += 8;
>        len -= 8;
>  }
> 
> -  Elena
> 
>> 
>> mkuper added a comment.
>> 
>> I tried building with r274114 (before this was reverted), and we did
>> generate a runtime alias check:
>> 
>> vector.memcheck:                                  ; preds = %min.iters.checked
>>   %7 = sub i32 -1, %len
>>   %8 = icmp sgt i32 %7, -9
>>   %smax9 = select i1 %8, i32 %7, i32 -9
>>   %9 = add i32 %len, %smax9
>>   %10 = add i32 %9, 8
>>   %11 = lshr i32 %10, 3
>>   %12 = zext i32 %11 to i64
>>   %13 = shl i64 %12, 3
>>   %scevgep = getelementptr i8, i8* %op, i64 %13
>>   %scevgep10 = getelementptr i8, i8* %src, i64 %13
>>   %bound0 = icmp ule i8* %op, %scevgep10
>>   %bound1 = icmp ule i8* %src, %scevgep
>>   %found.conflict = and i1 %bound0, %bound1
>>   %memcheck.conflict = and i1 %found.conflict, true
>>   %cast.crd = trunc i64 %n.vec to i32
>>   %14 = shl i32 %cast.crd, 3
>>   %ind.end = sub i32 %len, %14
>>   %15 = shl i64 %n.vec, 3
>>   %ind.end12 = getelementptr i8, i8* %op, i64 %15
>>   %ind.end14 = getelementptr i8, i8* %src, i64 %15
>>   br i1 %memcheck.conflict, label %scalar.ph, label %vector.ph
>> 
>> I'm not sure this runtime check is correct, though.
>> 
>> 
>> Repository:
>> rL LLVM
>> 
>> https://reviews.llvm.org/D20789
>> 
>> 
> 
> ---------------------------------------------------------------------
> Intel Israel (74) Limited
> 
> This e-mail and any attachments may contain confidential material for
> the sole use of the intended recipient(s). Any review or distribution
> by others is strictly prohibited. If you are not the intended
> recipient, please contact the sender and delete all copies.