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

[Demikhovsky, Elena 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?
[Demikhovsky, Elena] 
The error occurs when op - src = 0x1f

   >
   >> 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
   >>>

---------------------------------------------------------------------
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.