[Bug c/52283] New: "error: case label does not reduce to an integer constant" for constant folded cast expr

["chrbr at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52283

             Bug #: 52283
           Summary: "error: case label does not reduce to an integer
                    constant" for constant folded cast expr
    Classification: Unclassified
           Product: gcc
           Version: 4.6.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: chrbr@gcc.gnu.org


extern int u;

void b (int c)
{
  switch (c)
    {
    case (int) ( 2  | ( (4 < 8 ) ? 8 : u ) ) :
      break;
    }
}

fails with 
i.c:8:5: error: case label does not reduce to an integer constant

since GCC 4.6.2.

While is is legitimately a user error with respect to the standard, this brings
legacy issue for code that used to build with GCC 4.5. Note that GCC is usually
permissive with reduced integer constant use in case label, see PR39613. 

This change seems to have appeared with the removal of the lines in
c-common.c:check_case_value

  /* ??? Can we ever get nops here for a valid case value?  We
     shouldn't for C.  */
  STRIP_TYPE_NOPS (value);

so the check for INTEGER_CST now fails and fallthu into the error.