Simple bitop reassoc in match.pd

[Marc Glisse]

On Wed, 11 May 2016, Jeff Law wrote:

>> We could also simplify (int)(_Bool)x to x using VRP information that x
>> is in [0, 1], but apparently when VRP replaces x==0 with y=x^1,(_Bool)y,
>> it does not compute a range for the new variable y, and by the time the
>> next VRP pass comes, it is too late.
> Seems like a clear oversight.

In get_value_range, there is:
   /* If we query the range for a new SSA name return an unmodifiable VARYING.
      We should get here at most from the substitute-and-fold stage which
      will never try to change values.  */
so this is a known limitation.

We could try to change that (XRESIZEVEC, memset(0) on the new elements, 
update num_vr_values to the new num_ssa_names, at this point vr_value 
should be replaced with a vector).

We could also use set_range_info and make simplify_conversion_using_ranges 
use get_range_info instead of get_value_range. Might even move the whole 
function to match.pd then ;-)

-- 
Marc Glisse