[Bug c/18740] New: Execution-time sizeof drops side effects

[Bug c/18740] New: Execution-time sizeof drops side effects

[terra at gnome dot org]

The program below, which is a slight variation of a program from C99
section 6.5.3.4, contains an execution-time sizeof operator and its
argument should thus be evaluated.  Nevertheless, "i" in not incremented.

I would expect "i=1" to be printed.  I get "i=0".

(Sun's C compiler seems to do the same thing.)



#include <stdio.h>

size_t fsize3 (int n)
{
  int i = 0;
  char b[1][n+3];       // Variable length array.
  size_t s = sizeof (b[i++]);    // Execution time sizeof.
  printf ("i=%d\n", i);
  return s;
}

int main()
{
  size_t size;
  size = fsize3(10);
  return 0;
}

-- 
           Summary: Execution-time sizeof drops side effects
           Product: gcc
           Version: 3.4.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: terra at gnome dot org
                CC: gcc-bugs at gcc dot gnu dot org
 GCC build triplet: sparc-sun-solaris2.8
  GCC host triplet: sparc-sun-solaris2.8
GCC target triplet: sparc-sun-solaris2.8


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18740

[Bug c/18740] Execution-time sizeof drops side effects

[pinskia at gcc dot gnu dot org]

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |wrong-code


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18740

[Bug c/18740] Execution-time sizeof drops side effects

[bangerth at dealii dot org]

------- Additional Comments From bangerth at dealii dot org  2004-11-30 22:24 -------
That's not a bug. The standard says this: 
 
  5.3.3  Sizeof                                            [expr.sizeof] 
 
1 The  sizeof  operator  yields  the  number  of  bytes  in  the  object 
  representation of its operand.  The operand is either  an  expression, 
  which  is  not  evaluated,  or  a  parenthesized  type-id. 
 
W. 

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|                            |INVALID


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18740

[Bug c/18740] Execution-time sizeof drops side effects

[bangerth at dealii dot org]

------- Additional Comments From bangerth at dealii dot org  2004-11-30 22:48 -------
Actually, this requires more thought. I quoted from the C++ standard, but 
the bug is for C, and the problem lies here: the code is 
----------------- 
size_t fsize3 (int n) 
{ 
  int i = 0; 
  char b[1][n+3];       // Variable length array. 
  size_t s = sizeof (b[i++]); 
----------------- 
Indeed, b[0] is a VLA (or is it? maybe it's the GNU extension that looks 
so similar), and for that case, Morton pointed me correctly at 6.5.3.4/2 of 
the C99 standard, which has a special provision for this: 
  If the type of the operand is a variable length array type, the 
  operand is evaluated; otherwise the operand is not evaluated... 
 
Sorry for the confusion, 
 W. 
 
 
 
 

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|RESOLVED                    |UNCONFIRMED
         Resolution|INVALID                     |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18740

[Bug c/18740] Execution-time sizeof drops side effects

[jsm28 at gcc dot gnu dot org]

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jsm28 at gcc dot gnu dot org
OtherBugsDependingO|                            |16989
              nThis|                            |
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|                            |1
   Last reconfirmed|0000-00-00 00:00:00         |2004-12-01 01:44:07
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18740

[Bug c/18740] Execution-time sizeof drops side effects

[ebotcazou at gcc dot gnu dot org]

------- Additional Comments From ebotcazou at gcc dot gnu dot org  2004-12-21 11:15 -------
Reproducible on x86 and x86-64.


-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
  GCC build triplet|sparc-sun-solaris2.8        |*-*-*
   GCC host triplet|sparc-sun-solaris2.8        |*-*-*
 GCC target triplet|sparc-sun-solaris2.8        |*-*-*


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18740

[Bug c/18740] Execution-time sizeof drops side effects

[rth at gcc dot gnu dot org]

------- Additional Comments From rth at gcc dot gnu dot org  2004-12-21 13:39 -------
Not a bug.  Sizeof *never* has side effects.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |INVALID


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18740

[Bug c/18740] Execution-time sizeof drops side effects

[rth at gcc dot gnu dot org]

------- Additional Comments From rth at gcc dot gnu dot org  2004-12-21 13:43 -------
I'm wrong.  What a stupid thing to do to the C language.
Someone should be smacked.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|RESOLVED                    |REOPENED
         Resolution|INVALID                     |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18740

[Bug c/18740] Execution-time sizeof drops side effects

[pinskia at gcc dot gnu dot org]

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|REOPENED                    |NEW


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18740

[Bug c/18740] Execution-time sizeof drops side effects

[jsm28 at gcc dot gnu dot org]

------- Comment #8 from jsm28 at gcc dot gnu dot org  2006-06-04 17:01 -------
Fixed for 4.2.


-- 

jsm28 at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |FIXED
   Target Milestone|---                         |4.2.0


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18740

[Bug c/18740] Execution-time sizeof drops side effects

[mrs at gcc dot gnu dot org]

------- Comment #7 from mrs at gcc dot gnu dot org  2006-05-18 18:22 -------
Subject: Bug 18740

Author: mrs
Date: Thu May 18 18:22:12 2006
New Revision: 113888

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=113888
Log:
        Fix up vla, vm and [*] sematics.

        PR c/18740
        PR c/7948
        PR c/25802
        * c-tree.h (struct c_arg_info): Add had_vla_unspec.
        (c_vla_unspec_p): Add.
        (c_vla_type_p): Add.
        * c-decl.c (struct c_scope): Add had_vla_unspec.
        (build_array_declarator): Add support for [*].
        (grokdeclarator): Likewise.
        (grokparms): Likewise.
        (get_parm_info): Likewise.
        * c-objc-common.c (c_vla_unspec_p): Likewise.
        * c-objc-common.h (LANG_HOOKS_TREE_INLINING_VAR_MOD_TYPE_P): Likewise.
        * c-parser.c (c_parser_typeof_specifier): Evaluate arguments to
        typeof when argument is a variably modified type not inside sizeof or
alignof.
        (c_parser_direct_declarator_inner): Propagate errors.
        (c_parser_sizeof_expression): Add support for [*].
        * c-typeck.c (c_vla_type_p): Add.
        (composite_type): Add support for vla compositing.
        (comptypes_internal): Add support for vla compatibility.
        (c_expr_sizeof_expr): Evaluate vla arguments.
        * tree.c (variably_modified_type_p): Update comment for [*].

testsuite:
        * gcc.dg/c90-arraydecl-1.c: Update for vla, vm [*] fixups.
        * gcc.dg/vla-4.c: Add.
        * gcc.dg/vla-5.c: Add.
        * gcc.dg/vla-6.c: Add.

Added:
    trunk/gcc/testsuite/gcc.dg/vla-4.c
    trunk/gcc/testsuite/gcc.dg/vla-5.c
    trunk/gcc/testsuite/gcc.dg/vla-6.c
Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/c-decl.c
    trunk/gcc/c-objc-common.c
    trunk/gcc/c-objc-common.h
    trunk/gcc/c-parser.c
    trunk/gcc/c-tree.h
    trunk/gcc/c-typeck.c
    trunk/gcc/testsuite/ChangeLog
    trunk/gcc/testsuite/gcc.dg/c90-arraydecl-1.c
    trunk/gcc/tree.c


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18740

[Bug c/18740] Execution-time sizeof drops side effects

[mrs at apple dot com]

------- Comment #6 from mrs at apple dot com  2006-05-09 00:47 -------
I have a fix for this.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18740