[Bug c++/14932] New: cannot use offsetof to get offsets of array elements in g++ 3.4.0 prerelease

[Bug c++/14932] New: cannot use offsetof to get offsets of array elements in g++ 3.4.0 prerelease

[bhelf at flitterfly dot whirpon dot com]

In the gcc 3.4.0 prerelase, taking the offset of an array element works in gcc
but not in g++.  This does work in 3.3.x and earlier versions of g++.


Version:
g++ (GCC) 3.4.0 20040407 (prerelease)

System:
i686-pc-linux-gnu  Red Hat 9  AthlonXP

GCC Configuration:
/usr2/stow/gcc/3.4.0_prerelease/gcc-3.4.0-20040406/configure
--prefix=/usr2/stow/gcc/3.4.0_prerelease/ --enable-languages=c,c++

GCC Invocation:
/usr2/stow/gcc/3.4.0_prerelease/bin/g++ tt.c

GCC Output:
tt.c: In function `int main(int, char**)':
tt.c:16: error: an array reference cannot appear in a constant-expression

Testcase (unpreprocessed):

#include <stddef.h>

#ifdef __cplusplus
extern "C" int printf (__const char *__restrict __format, ...);
#endif

struct foobar
{
    int bar;
    int foo[22];
};

int main(int argc, char **argv)
{
    printf("%u\n", (unsigned)offsetof(struct foobar, foo[12]));
}



Testcase (preprocessed):
# 1 "tt.c"
# 1 "<built-in>"
# 1 "<command line>"
# 1 "tt.c"

# 1
"/usr2/stow/gcc/3.4.0_prerelease/bin/../lib/gcc/i686-pc-linux-gnu/3.4.0/include/stddef.h"
1 3 4
# 151
"/usr2/stow/gcc/3.4.0_prerelease/bin/../lib/gcc/i686-pc-linux-gnu/3.4.0/include/stddef.h"
3 4
typedef int ptrdiff_t;
# 213
"/usr2/stow/gcc/3.4.0_prerelease/bin/../lib/gcc/i686-pc-linux-gnu/3.4.0/include/stddef.h"
3 4
typedef unsigned int size_t;
# 3 "tt.c" 2


extern "C" int printf (__const char *__restrict __format, ...);


struct foobar
{
    int bar;
    int foo[22];
};

int main(int argc, char **argv)
{
    printf("%u\n", (unsigned)(__offsetof__ (reinterpret_cast <size_t>
(&reinterpret_cast <char &> (static_cast<struct foobar *> (0)->foo[12])))));
}

-- 
           Summary: cannot use offsetof to get offsets of array elements in
                    g++ 3.4.0 prerelease
           Product: gcc
           Version: 3.4.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: bhelf at flitterfly dot whirpon dot com
                CC: gcc-bugs at gcc dot gnu dot org
 GCC build triplet: i686-pc-linux-gnu
  GCC host triplet: i686-pc-linux-gnu
GCC target triplet: i686-pc-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=14932

[Bug c++/14932] [3.4/3.5 Regression] cannot use offsetof to get offsets of array elements in g++ 3.4.0 prerelease

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2004-04-13 01:53 -------
I have a fix for 3.5.0 if this is a valid code as I think it is.  But it is too invasive fix for 3.4.x.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |rejects-valid
            Summary|cannot use offsetof to get  |[3.4/3.5 Regression] cannot
                   |offsets of array elements in|use offsetof to get offsets
                   |g++ 3.4.0 prerelease        |of array elements in g++
                   |                            |3.4.0 prerelease
   Target Milestone|---                         |3.4.1


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=14932

[Bug c++/14932] [3.4/3.5 Regression] cannot use offsetof to get offsets of array elements in g++ 3.4.0 prerelease

[giovannibajo at libero dot it]

------- Additional Comments From giovannibajo at libero dot it  2004-04-14 10:15 -------
Not sure how your fix looks like, but the correct fix looks to me a one liner 
in parser.c, where it checks if '[]' is allowed in constant expressions. The 
code is valid.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|                            |1
   Last reconfirmed|0000-00-00 00:00:00         |2004-04-14 10:15:19
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=14932

[Bug c++/14932] [3.4/3.5 Regression] cannot use offsetof to get offsets of array elements in g++ 3.4.0 prerelease

[bhelf at flitterfly dot whirpon dot com]

------- Additional Comments From bhelf at flitterfly dot whirpon dot com  2004-04-27 04:55 -------
I added a one-liner check for !in_offsetof_p to the code in parser.c that
detects the case of an array index and it does seem to fix the problem.  Here's
the patch that I tried.  No regressions in the testsuite (tested on
i686-pc-linux-gnu).

Index: parser.c
===================================================================
RCS file: /cvsroot/gcc/gcc/gcc/cp/parser.c,v
retrieving revision 1.157.2.25
diff -u -c -r1.157.2.25 parser.c
*** parser.c    19 Mar 2004 11:41:15 -0000      1.157.2.25
--- parser.c    27 Apr 2004 04:46:47 -0000
***************
*** 3705,3712 ****
            idk = CP_ID_KIND_NONE;
            /* Array references are not permitted in
               constant-expressions.  */
!           if (cp_parser_non_integral_constant_expression
!               (parser, "an array reference"))
              postfix_expression = error_mark_node;
          }
          break;
--- 3705,3715 ----
            idk = CP_ID_KIND_NONE;
            /* Array references are not permitted in
               constant-expressions.  */
!           if (/* The "[]" operator is allowed in the implementation
!                  of "offsetof".  */
!               !parser->in_offsetof_p
!               && (cp_parser_non_integral_constant_expression
!                   (parser, "an array reference")))
              postfix_expression = error_mark_node;
          }
          break;


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=14932

[Bug c++/14932] [3.4/3.5 Regression] cannot use offsetof to get offsets of array elements in g++ 3.4.0 prerelease

[giovannibajo at libero dot it]

------- Additional Comments From giovannibajo at libero dot it  2004-04-27 07:11 -------
That is the patch I was thinking of. You want to take care of asking for 
approval yourself? Otherwise I can take care of it.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |giovannibajo at libero dot
                   |                            |it


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=14932

[Bug c++/14932] [3.4/3.5 Regression] cannot use offsetof to get offsets of array elements in g++ 3.4.0 prerelease

[bangerth at dealii dot org]

------- Additional Comments From bangerth at dealii dot org  2004-04-27 12:45 -------
Giovanni, please take care of this -- patches from unknown contributors 
are unfortunately too often ignored :-( 
 
W. 

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |patch


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=14932

[Bug c++/14932] [3.4/3.5 Regression] cannot use offsetof to get offsets of array elements in g++ 3.4.0 prerelease

[bhelf at flitterfly dot whirpon dot com]

------- Additional Comments From bhelf at flitterfly dot whirpon dot com  2004-04-27 20:47 -------
Giovanni, 

If you could request it, that'd be great!  The patch is just based on your
comment #2 and I thought it might be helpful to do the quick cut-n-paste and run
the regression tests.  

I don't have all the paperwork in place to actually submit patches, however.  I
don't have a good idea what the dividing line between a trivial and a nontrivial
patch is, but I do know that all I did was copy an if clause from elsewhere in
that file, so I didn't really _write_ anything.

And I suspect that Wolfgang's comment has truth to it as well.

Thank you all for your help and comments and for your work on such a cool project!

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=14932

[Bug c++/14932] [3.4/3.5 Regression] cannot use offsetof to get offsets of array elements in g++ 3.4.0 prerelease

[giovannibajo at libero dot it]

------- Additional Comments From giovannibajo at libero dot it  2004-04-27 23:35 -------
Not that my patches are being reviewed that much lately, but I'll add this to 
the can ;)

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
         AssignedTo|unassigned at gcc dot gnu   |giovannibajo at libero dot
                   |dot org                     |it
             Status|NEW                         |ASSIGNED


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=14932

[Bug c++/14932] [3.4/3.5 Regression] cannot use offsetof to get offsets of array elements in g++ 3.4.0 prerelease

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2004-05-03 19:03 -------
*** Bug 15270 has been marked as a duplicate of this bug. ***

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |sebor at roguewave dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=14932

[Bug c++/14932] [3.4/3.5 Regression] cannot use offsetof to get offsets of array elements in g++ 3.4.0 prerelease

[giovannibajo at libero dot it]

------- Additional Comments From giovannibajo at libero dot it  2004-06-01 02:33 -------
Patch submitted:
http://gcc.gnu.org/ml/gcc-patches/2004-06/msg00004.html

waiting for review (Mark?)


-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |mmitchel at gcc dot gnu dot
                   |                            |org
      Known to fail|                            |3.4.0 3.5.0
      Known to work|                            |3.3.3


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=14932

[Bug c++/14932] [3.4/3.5 Regression] cannot use offsetof to get offsets of array elements in g++ 3.4.0 prerelease

[cvs-commit at gcc dot gnu dot org]

------- Additional Comments From cvs-commit at gcc dot gnu dot org  2004-06-01 10:22 -------
Subject: Bug 14932

CVSROOT:	/cvs/gcc
Module name:	gcc
Changes by:	giovannibajo@gcc.gnu.org	2004-06-01 10:22:12

Modified files:
	gcc/cp         : ChangeLog parser.c 
	gcc/testsuite  : ChangeLog 
Added files:
	gcc/testsuite/g++.dg/parse: offsetof4.C 

Log message:
	PR c++/14932
	* parser.c (cp_parser_postfix_expression): Allow subscript
	operator in offsetof.
	
	PR c++/14932
	* g++.dg/parse/offsetof4.C: New test.

Patches:
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/cp/ChangeLog.diff?cvsroot=gcc&r1=1.4072&r2=1.4073
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/cp/parser.c.diff?cvsroot=gcc&r1=1.197&r2=1.198
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/testsuite/ChangeLog.diff?cvsroot=gcc&r1=1.3801&r2=1.3802
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/testsuite/g++.dg/parse/offsetof4.C.diff?cvsroot=gcc&r1=NONE&r2=1.1



-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=14932

[Bug c++/14932] [3.4/3.5 Regression] cannot use offsetof to get offsets of array elements in g++ 3.4.0 prerelease

[cvs-commit at gcc dot gnu dot org]

------- Additional Comments From cvs-commit at gcc dot gnu dot org  2004-06-01 10:47 -------
Subject: Bug 14932

CVSROOT:	/cvs/gcc
Module name:	gcc
Branch: 	gcc-3_4-branch
Changes by:	giovannibajo@gcc.gnu.org	2004-06-01 10:47:00

Modified files:
	gcc/cp         : ChangeLog parser.c 
	gcc/testsuite  : ChangeLog 
Added files:
	gcc/testsuite/g++.dg/parse: offsetof4.C 

Log message:
	PR c++/14932
	* parser.c (cp_parser_postfix_expression): Allow subscript
	operator in offsetof.
	
	PR c++/14932
	* g++.dg/parse/offsetof4.C: New test.

Patches:
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/cp/ChangeLog.diff?cvsroot=gcc&only_with_tag=gcc-3_4-branch&r1=1.3892.2.111&r2=1.3892.2.112
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/cp/parser.c.diff?cvsroot=gcc&only_with_tag=gcc-3_4-branch&r1=1.157.2.29&r2=1.157.2.30
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/testsuite/ChangeLog.diff?cvsroot=gcc&only_with_tag=gcc-3_4-branch&r1=1.3389.2.194&r2=1.3389.2.195
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/testsuite/g++.dg/parse/offsetof4.C.diff?cvsroot=gcc&only_with_tag=gcc-3_4-branch&r1=NONE&r2=1.1.2.1



-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=14932

[Bug c++/14932] [3.4/3.5 Regression] cannot use offsetof to get offsets of array elements in g++ 3.4.0 prerelease

[giovannibajo at libero dot it]

------- Additional Comments From giovannibajo at libero dot it  2004-06-01 10:49 -------
Fixed for 3.4.1 and 3.5.0. Thank you for your report (and for your patch)!

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


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=14932

[Bug c++/14932] [3.4/3.5 Regression] cannot use offsetof to get offsets of array elements in g++ 3.4.0 prerelease

[giovannibajo at libero dot it]

------- Additional Comments From giovannibajo at libero dot it  2004-08-04 00:18 -------
*** Bug 16868 has been marked as a duplicate of this bug. ***

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |ppluzhnikov at charter dot
                   |                            |net


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=14932