[Bug tree-optimization/69042] [6 regression] Missed optimization in ivopts

[amker at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69042

amker at gcc dot gnu.org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |amker at gcc dot gnu.org

--- Comment #2 from amker at gcc dot gnu.org ---
For iv use:
use 0
  address
  in statement _9 = indexes[i_23];

  at position indexes[i_23]
  type const int *
  base (const int *) (&indexes + 4)
  step 4
  base object (void *) &indexes
  related candidates 

Before the change, two candidates are added:
candidate 8
  var_before ivtmp.12
  var_after ivtmp.12
  incremented before exit test
  type unsigned int
  base (unsigned int) (&indexes + 4)
  step 4
  base object (void *) &indexes
candidate 10
  var_before ivtmp.14
  var_after ivtmp.14
  incremented before exit test
  type unsigned int
  base (unsigned int) &indexes
  step 4
  base object (void *) &indexes
After the change only candidate 8 is added.  I did this to minimize the number
of candidates.  Maybe that's too aggressive.  Probably candidate like this
(with offset stripped) should be added, I will check if it causes new
regressions.

Another problem is candidate 8 could be chosen to decrease register pressure,
but isn't.  I will check why the register pressure cost doesn't work in this
case.  Though candidate 8 is still a little bit worse than candidate 10,
because of one more setup instruction in loop pre-header block.