[Bug middle-end/31023] New: Fold is agnostic of integer sub-types

[Bug middle-end/31023] New: Fold is agnostic of integer sub-types

[rguenth at gcc dot gnu dot org]

Transformations in fold do not properly handle integer types with value ranges
(defined by TYPE_MIN_VALUE and TYPE_MAX_VALUE) that do not correspond to the
types precision.

Citing from PR30911 comment #40

"The problem is in this transformation:

      /* Fold (X & C) op (Y & C) as (X ^ Y) & C op 0", and symmetries.  */

X^Y may not be in the range of the type.  In this case C=7 and op=NE_EXPR.
The type of X and Y has range 4..5.  Thus X^Y is either 0 or 2 (neither of
which is in the range 4..5).  Since the type of X^Y has range 4..5, the
new fold code deduces that X^Y NE 0 is always true.  I think the thing to
do, as Richard Kenner suggested, is to convert each type to its base type
right at the start of fold_comparison, at least if it has a base type
(the same goes for other routines in fold).  This unfortunately neutralizes
your patch, since as it is right now you will only ever see base types.
Thus this kind of check needs to happen at the start of fold_comparison,
before the conversion to the base type."

another source of problems is fold_convert and its siblings that happily
create out-of-bounds constants or strip conversions to the base type.


-- 
           Summary: Fold is agnostic of integer sub-types
           Product: gcc
           Version: 4.3.0
            Status: UNCONFIRMED
          Keywords: wrong-code
          Severity: normal
          Priority: P3
         Component: middle-end
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: rguenth at gcc dot gnu dot org
OtherBugsDependingO 30911
             nThis:


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31023

[Bug middle-end/31023] Fold is agnostic of integer sub-types

[ebotcazou at gcc dot gnu dot org]

-- 

ebotcazou at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |ebotcazou at gcc dot gnu dot
                   |                            |org
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|0                           |1
   Last reconfirmed|0000-00-00 00:00:00         |2007-09-12 16:05:25
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31023

[Bug middle-end/31023] Fold is agnostic of integer sub-types

[rguenth at gcc dot gnu dot org]

------- Comment #1 from rguenth at gcc dot gnu dot org  2008-03-30 14:57 -------
Subject: Bug 31023

Author: rguenth
Date: Sun Mar 30 14:56:28 2008
New Revision: 133731

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=133731
Log:
2008-03-30  Richard Guenther  <rguenther@suse.de>

        PR middle-end/31023
        * fold-const.c (fold_sign_changed_comparison): Do leave
        conversions to base-types alone.

Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/fold-const.c


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31023

[Bug middle-end/31023] Fold is agnostic of integer sub-types

[ebotcazou at gcc dot gnu dot org]

------- Comment #2 from ebotcazou at gcc dot gnu dot org  2009-11-10 08:34 -------
These sub-types are gone in 4.5.


-- 

ebotcazou at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |WONTFIX
   Target Milestone|---                         |4.5.0


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31023