[Bug c/13519] New: typeof(nonconst+const) is const

[Bug c/13519] New: typeof(nonconst+const) is const

[debian-gcc at lists dot debian dot org]

[forwarded from http://bugs.debian.org/208981]

Bug submitter writes:

Try compiling the following function with "gcc-3.3 -c const.c".
GCC gives "assignment of read-only variable" warnings on the
indicated lines.  This shows that __typeof__ treats the
corresponding arguments as const.

void fn(void)
{
  int n;
  const int c;

  { __typeof__(n) a1; a1=0; }
  { __typeof__(c) a2; a2=0; }	/* warning */

  { __typeof__(n+n) b0; b0=0; }
  { __typeof__(n+c) b1; b1=0; }	/* warning */
  { __typeof__(c+n) b2; b2=0; }
  { __typeof__(c+c) b3; b3=0; }	/* warning */

  { __typeof__(1+n) c0; c0=0; }
  { __typeof__(1+c) c1; c1=0; }	/* warning */
  { __typeof__(n+1) c2; c2=0; }
  { __typeof__(c+1) c3; c3=0; }

  { __typeof__(((int)n)+((int)n)) d0; d0=0; }
  { __typeof__(((int)n)+((int)c)) d1; d1=0; } /* warning */
  { __typeof__(((int)c)+((int)n)) d2; d2=0; }
  { __typeof__(((int)c)+((int)c)) d3; d3=0; } /* warning */

  { __typeof__(((const int)n)+((const int)n)) e0; e0=0; }
  { __typeof__(((const int)n)+((const int)c)) e1; e1=0; } /* warning */
  { __typeof__(((const int)c)+((const int)n)) e2; e2=0; }
  { __typeof__(((const int)c)+((const int)c)) e3; e3=0; } /* warning */
}

The behavior at b1 and b2 seems inconsistent.  If n+c is const,
then surely c+n should be as well, given that the addition
operator is commutative in all other respects.

Cases c0 to c3 show that GCC treats an integer constant as a
non-const rvalue.  Cases d0 to d3 and e0 to e3 show that casts
have no effect on the constness of the result; that can't be
right either.

I think it would be cleanest to make the addition operator always
return a non-const rvalue, regardless of whether the operands are
const.  After all, the result is supposed to be freshly computed.

-- 
           Summary: typeof(nonconst+const) is const
           Product: gcc
           Version: 3.4.0
            Status: UNCONFIRMED
          Severity: minor
          Priority: P2
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: debian-gcc at lists dot debian dot org
                CC: gcc-bugs at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=13519

[Bug c/13519] typeof(nonconst+const) is const

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2003-12-30 17:56 -------
typeof just returns the type of the tree which it is bound to, so it looks like the front-end is getting 
the type wrong.

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=13519

[Bug c/13519] typeof(nonconst+const) is const

[dhazeghi at yahoo dot com]

------- Additional Comments From dhazeghi at yahoo dot com  2004-01-18 08:18 -------
Confirmed with 3.4 branch/mainline.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|                            |1
           Keywords|                            |diagnostic
   Last reconfirmed|0000-00-00 00:00:00         |2004-01-18 08:18:12
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=13519

[Bug c/13519] typeof(nonconst+const) is const

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2004-05-27 18:44 -------
More to the point, now that the warnings are turned into errors in 3.4.0 and the mainline.  I think the 
problem is that the C front-end is taking the left side of the tree for the type.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|2004-01-18 08:18:12         |2004-05-27 18:44:12
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=13519

[Bug c/13519] typeof(nonconst+const) is const

[cvs-commit at gcc dot gnu dot org]

------- Additional Comments From cvs-commit at gcc dot gnu dot org  2004-06-06 15:22 -------
Subject: Bug 13519

CVSROOT:	/cvs/gcc
Module name:	gcc
Changes by:	jsm28@gcc.gnu.org	2004-06-06 15:21:59

Modified files:
	gcc            : ChangeLog c-decl.c c-tree.h c-typeck.c 
	gcc/testsuite  : ChangeLog 
Added files:
	gcc/testsuite/gcc.c-torture/execute: enum-3.c 
	gcc/testsuite/gcc.dg: pr13519-1.c 

Log message:
	PR c/13519
	* c-typeck.c (composite_type, common_pointer_type): New functions.
	(common_type): Split parts into composite_type and
	common_pointer_type.  Ensure that arithmetic operations return
	unqualified types without attributes.  Don't make composite type
	of signed enum and compatible integer be unsigned.
	(build_conditional_expr, build_binary_op): Use
	common_pointer_type.
	* c-decl.c (merge_decls): Use composite_type.
	* c-tree.h (composite_type): Declare.
	
	testsuite:
	* gcc.c-torture/enum-3.c, gcc.dg/pr13519-1.c: New tests.

Patches:
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/ChangeLog.diff?cvsroot=gcc&r1=2.3853&r2=2.3854
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/c-decl.c.diff?cvsroot=gcc&r1=1.504&r2=1.505
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/c-tree.h.diff?cvsroot=gcc&r1=1.147&r2=1.148
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/c-typeck.c.diff?cvsroot=gcc&r1=1.308&r2=1.309
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/testsuite/ChangeLog.diff?cvsroot=gcc&r1=1.3812&r2=1.3813
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/testsuite/gcc.c-torture/execute/enum-3.c.diff?cvsroot=gcc&r1=NONE&r2=1.1
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/testsuite/gcc.dg/pr13519-1.c.diff?cvsroot=gcc&r1=NONE&r2=1.1



-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=13519

[Bug c/13519] typeof(nonconst+const) is const

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2004-06-06 15:51 -------
Fixed in 3.5.0

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |FIXED
   Target Milestone|---                         |3.5.0


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=13519