[Bug c/66341] New: Some casts wrongly produce a lvalue

[Bug c/66341] New: Some casts wrongly produce a lvalue

[kp.lehrmann+gcc at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66341

            Bug ID: 66341
           Summary: Some casts wrongly produce a lvalue
           Product: gcc
           Version: 5.1.0
            Status: UNCONFIRMED
          Severity: minor
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: kp.lehrmann+gcc at gmail dot com
  Target Milestone: ---

Created attachment 35653
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=35653&action=edit
gcc compiles ok instead of producing a "error: lvalue required as left operand
of assignment"

Hello,

gcc (any version that I tried) allows some casts to produce a lvalue, whereas
"error: lvalue required as left operand of assignment" would be expected.

Basically, cast of the following form wrongly compile:

    struct B{ int *c;};
    struct A{ struct B b;};
    struct A  a;

    int d = 5;
    (int*)((struct A *)(&a)->b.c) = &d;

Note that if the first cast (int*) is replaced by a cast to any type but the
type of the member in struct B, the expected error message is produced.

For instance, 
    (char*)((struct A *)(&a)->b.c) = &d;
produce the expected error.

Best regards

[Bug c/66341] Some casts wrongly produce a lvalue

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66341

Martin Sebor <msebor at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2015-05-30
                 CC|                            |msebor at gcc dot gnu.org
     Ever confirmed|0                           |1

--- Comment #1 from Martin Sebor <msebor at gcc dot gnu.org> ---
Confirmed with both gcc and g++ 5.1.0.  Below is a slightly smaller test case
along with Clang output.

$ cat t.c && gcc -Wall -c t.c && clang t.c
struct A { int *i; };

void foo (struct A *a)
{
    (int*)(struct A*)a->i = a->i;
}

t.c:5:27: error: expression is not assignable
    (int*)(struct A*)a->i = a->i;
    ~~~~~~~~~~~~~~~~~~~~~ ^
1 error generated.

[Bug c/66341] Some casts wrongly produce a lvalue

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66341

Marek Polacek <mpolacek at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED
                 CC|                            |mpolacek at gcc dot gnu.org
           Assignee|unassigned at gcc dot gnu.org      |mpolacek at gcc dot gnu.org

[Bug c/66341] Some casts wrongly produce a lvalue

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66341

Marek Polacek <mpolacek at gcc dot gnu.org> changed:

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

--- Comment #3 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
Fixed.

[Bug c/66341] Some casts wrongly produce a lvalue

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66341

--- Comment #2 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
Author: mpolacek
Date: Thu Jun  4 08:17:45 2015
New Revision: 224115

URL: https://gcc.gnu.org/viewcvs?rev=224115&root=gcc&view=rev
Log:
        PR c/66341
        * c-typeck.c (build_c_cast): Wrap VALUE into NON_LVALUE_EXPR if
        it is a lvalue.

        * gcc.dg/lvalue-8.c: New test.

Added:
    trunk/gcc/testsuite/gcc.dg/lvalue-8.c
Modified:
    trunk/gcc/c/ChangeLog
    trunk/gcc/c/c-typeck.c
    trunk/gcc/testsuite/ChangeLog

[Bug c/66341] Some casts wrongly produce a lvalue

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66341

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |6.0