[Bug middle-end/55863] New: Fails to fold (i + 2) - (i + 1) to 1

[Bug middle-end/55863] New: Fails to fold (i + 2) - (i + 1) to 1

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55863

             Bug #: 55863
           Summary: Fails to fold (i + 2) - (i + 1) to 1
    Classification: Unclassified
           Product: gcc
           Version: 4.8.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: normal
          Priority: P3
         Component: middle-end
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: rguenth@gcc.gnu.org


For

(analyze_overlapping_iterations
  (chrec_a = {pretmp_1529 + 1, +, 1}_20)
  (chrec_b = {pretmp_1529 + 2, +, 1}_20)

The SIV test currently fails because when computing the difference
between the CHRECs we compute pretmp_1529 + 2 + ~pretmp15_29.  This
is because when computing A - B we check if B is easy to negate - which
X + 1 is - and compute it as A + ~X which association then fails to
optimize.

This makes dependence tests of this kind fail.

[Bug middle-end/55863] Fails to fold (i + 2) - (i + 1) to 1

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55863

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |ASSIGNED
   Last reconfirmed|                            |2013-01-03
         AssignedTo|unassigned at gcc dot       |rguenth at gcc dot gnu.org
                   |gnu.org                     |
     Ever Confirmed|0                           |1

--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> 2013-01-03 14:29:25 UTC ---
I have a patch.

[Bug middle-end/55863] Fails to fold (i + 2) - (i + 1) to 1

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55863

--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> 2013-01-04 10:45:44 UTC ---
Author: rguenth
Date: Fri Jan  4 10:45:37 2013
New Revision: 194899

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=194899
Log:
2013-01-04  Richard Biener  <rguenther@suse.de>

    PR middle-end/55863
    * fold-const.c (split_tree): Undo -X - 1 to ~X folding for
    reassociation.

    * gcc.dg/fold-reassoc-2.c: New testcase.

Added:
    trunk/gcc/testsuite/gcc.dg/fold-reassoc-2.c
Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/fold-const.c
    trunk/gcc/testsuite/ChangeLog

[Bug middle-end/55863] Fails to fold (i + 2) - (i + 1) to 1

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55863

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

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

--- Comment #3 from Richard Biener <rguenth at gcc dot gnu.org> 2013-01-04 10:46:31 UTC ---
Fixed.