[Bug tree-optimization/52254] New: VRP does not fold (~a) & N to a ^ N if a has range [0, N]

[Bug tree-optimization/52254] New: VRP does not fold (~a) & N to a ^ N if a has range [0, N]

[pinskia at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52254

             Bug #: 52254
           Summary: VRP does not fold (~a) & N to a ^ N if a has range [0,
                    N]
    Classification: Unclassified
           Product: gcc
           Version: 4.7.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: pinskia@gcc.gnu.org


While working on moving fold-const.c bit expression optimizations to a SSA
based optimization, I found that if we optimize (a^N)&N to ~a & N, VRP does not
change that to just a ^ N.
Simple example:
/* { dg-do compile } */
/* { dg-options "-O2 -fno-tree-ccp -fdump-tree-vrp1" } */

int f(int x)
{
  if (x >= 0 && x <= 3)
    {
      x = (x ^ 3) & 3;
    }
  return x;
}

/* { dg-final { scan-tree-dump-times " & 3;" 0 "vrp1" { xfail *-*-* } } } */
/* { dg-final { cleanup-tree-dump "vrp1" } } */

[Bug tree-optimization/52254] VRP does not fold (~a) & N to a ^ N if a has range [0, N]

[pinskia at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52254

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |missed-optimization
             Status|UNCONFIRMED                 |ASSIGNED
   Last reconfirmed|                            |2012-02-15
         AssignedTo|unassigned at gcc dot       |pinskia at gcc dot gnu.org
                   |gnu.org                     |
     Ever Confirmed|0                           |1

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> 2012-02-15 00:23:42 UTC ---
I am going to work on this with my combine patches, I am thinking about
allowing VRP to supply a range to the combine stage and we should be able to
use that info to do the folding there (in a more common place too).

[Bug tree-optimization/52254] VRP does not fold (~a) & N to a ^ N if a has range [0, N]

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52254

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Severity|normal                      |enhancement

--- Comment #2 from Richard Guenther <rguenth at gcc dot gnu.org> 2012-02-15 11:21:53 UTC ---
The combine stage should have access to a valueize() hook as well, to query
SSA propagator/VNs lattice.  That hook can maybe supply this extra info
(I wanted to make VRP info persistent for some time, in SSA_NAME_PTR_INFO
much like we have alignment info there which really is kind of a value-range)

[Bug tree-optimization/52254] VRP does not fold (~a) & N to a ^ N if a has range [0, N]

[pinskia at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52254

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> 2012-02-16 03:00:22 UTC ---
(In reply to comment #2)
> The combine stage should have access to a valueize() hook as well, to query
> SSA propagator/VNs lattice.  That hook can maybe supply this extra info
> (I wanted to make VRP info persistent for some time, in SSA_NAME_PTR_INFO
> much like we have alignment info there which really is kind of a value-range)

I was thinking about adding that.  Even using nonzero bits to create a simple
range.

[Bug tree-optimization/52254] VRP does not fold (~a) & N to a ^ N if a has range [0, N]

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=52254

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |FIXED
             Status|ASSIGNED                    |RESOLVED
   Target Milestone|---                         |7.0

--- Comment #4 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Was fixed with r7-820 which adds the pattern to match.pd.