[Bug tree-optimization/87954] VRP can transform a * b where a,b are [0,1] to a & b

[aldyh at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87954

Aldy Hernandez <aldyh at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2018-11-09
     Ever confirmed|0                           |1

--- Comment #1 from Aldy Hernandez <aldyh at gcc dot gnu.org> ---
Indeed, if you compile imul() with -fdump-tree-all-details-alias -O2 and look
at the vrp1 dump, one can see:

  # RANGE [0, 1] NONZERO 1
  is_rec_12 = (int) _4;
...
  # RANGE [0, 1] NONZERO 1
  _6 = (int) _15;
  # RANGE [0, 1] NONZERO 1
  _7 = _6 * is_rec_12;

This pattern persists throughout the optimization pipeline, so any remaining
optimizer could potentially see the range of the operands and strength reduce
this.

What would be the best place to do this?