[Bug tree-optimization/42436] New: VRP should mark non-trapping integer divisions

[Bug tree-optimization/42436] New: VRP should mark non-trapping integer divisions

[rguenth at gcc dot gnu dot org]

In PR42108 a division is found to be non-trapping by VRP but neither PRE nor
LIM can make use of that information (well, because VRP doesn't mark the
divisions in any meaningful way).


-- 
           Summary: VRP should mark non-trapping integer divisions
           Product: gcc
           Version: 4.5.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: enhancement
          Priority: P3
         Component: tree-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: rguenth at gcc dot gnu dot org
OtherBugsDependingO 42108
             nThis:


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42436

[Bug tree-optimization/42436] VRP should mark non-trapping integer divisions

[rguenth at gcc dot gnu dot org]

------- Comment #1 from rguenth at gcc dot gnu dot org  2009-12-19 19:42 -------
I'll take care of this during 4.6 development.


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         AssignedTo|unassigned at gcc dot gnu   |rguenth at gcc dot gnu dot
                   |dot org                     |org
             Status|UNCONFIRMED                 |ASSIGNED
     Ever Confirmed|0                           |1
   Last reconfirmed|0000-00-00 00:00:00         |2009-12-19 19:42:12
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42436

[Bug tree-optimization/42436] VRP should mark non-trapping integer divisions

[amacleod at redhat dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=42436

--- Comment #3 from Andrew Macleod <amacleod at redhat dot com> ---
What needs to be done here? anything?  

Looking at VRP1, there is only a single divide left at that point:

countm1.6_54 = _12 / _13;

and VRP1 is setting the global range of _13 to:

_13: unsigned int [2, 2147483647]

So at least from that point on, it is trivial to determine the divide is
non-trapping even using the global ranges.

[Bug tree-optimization/42436] VRP should mark non-trapping integer divisions

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=42436

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |FIXED
             Status|NEW                         |RESOLVED

--- Comment #4 from Richard Biener <rguenth at gcc dot gnu.org> ---
I think this was trying to cover things like

  if (d != 0)
    tem = a / d;

where the non-zero range of d on the division cannot be put in global ranges
for its SSA name since that would be incorrect for uses not guarded by the
condition.  So it would ask for a new flag on GIMPLE statements to mark the
division not trapping (like we have TREE_THIS_NOTRAP).  Transforms like
PRE or LIM that do code motion of course have to be careful to not move
the stmt outside of the condition that made it not trapping - something which
would be as hard to guarantee as computing the non-trappingness in the first
place.

So yes, the case that made me file this bug is fixed with global ranges.

Let's close this bug since it's quite unspecific.