[Bug tree-optimization/32377] can't determine dependence (source/destination overlap without more than size)

["irar at il dot ibm dot com" <gcc-bugzilla at gcc dot gnu dot org>]

------- Comment #7 from irar at il dot ibm dot com  2007-07-03 12:57 -------
(In reply to comment #6)
> Distance vectors are lexicographically positive vectors, that is why you get
> the 1
> in all these cases.  If you want to know which one comes first, you have to
> look
> at the DR_IS_READ for both references in the dependence relation.

I am sorry, but I still don't understand.

For 
  for (i = 0; i < N; i++){
    ia[i+1] = ia[i] * 4;
  }
the ddr is {ld, st} and distance 1

and for
  for (i = 0; i < N; i++){
    ia[i] = ia[i+1] * 4;
  }
the ddr is also {ld, st} with distance 1.

How can we distinguish between these cases? 

Thanks,
Ira


-- 

irar at il dot ibm dot com changed:

           What    |Removed                     |Added
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                 CC|                            |irar at il dot ibm dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32377