[Bug tree-optimization/37869] New: PTA results wrong for "non-pointer" variables

[rguenth at gcc dot gnu dot org]

For the testcase

typedef struct cpp_token { int type; } cpp_token;
typedef struct _cpp_buff { struct _cpp_buff *next; } _cpp_buff;
extern cpp_token *cpp_get_token ();
extern _cpp_buff *cpp_get_buff ();
static void collect_args (_cpp_buff **pragma_buff)
{
  cpp_token *token = _cpp_get_token ();
  do {
      if (*pragma_buff == ((void *)0))
        {
          _cpp_buff *next = *pragma_buff;
          *pragma_buff = _cpp_get_buff ();
          (*pragma_buff)->next = next;
        }
      token = cpp_get_token ();
  } while (token->type != 0);
}
void enter_macro_context ()
{
  _cpp_buff *pragma_buff = ((void *)0);
  collect_args (&pragma_buff);
}

PTA figures that one of the SSA_NAMEs of pragma_buff is a "non-pointer"
variable which makes it ignore its constraints.  We end up with an empty
PTA solution even though we do dereference this pointer:

pragma_buff_4 = &ANYTHING
pragma_buff_11 = pragma_buff_4
pragma_buff_5 = pragma_buff_11
*pragma_buff_5 = pragma_buff_2

Equivalence classes for Direct node node id 16:pragma_buff_5 are pointer: 0,
location:0

pragma_buff_5 is a non-pointer variable, eliminating edges.

pragma_buff_5 is a non-pointer variable,ignoring constraint:pragma_buff_5 =
pragma_buff_11
pragma_buff_5 is a non-pointer variable,ignoring constraint:*pragma_buff_5 =
pragma_buff_2

pragma_buff_5 = { }

<bb 4>:
  pragma_buff_2 = pragma_buff_8;
  D.1263_3 = _cpp_get_buff ();
  pragma_buff_4 = (struct _cpp_buff *) D.1263_3;
  pragma_buff_11 = pragma_buff_4;
  pragma_buff_5 = pragma_buff_11;
  pragma_buff_5->next = pragma_buff_2;


We are "safe" from this error only because an empty points-to solution is
treated the same as a points-to-anything solution by the operand scanner.


-- 
           Summary: PTA results wrong for "non-pointer" variables
           Product: gcc
           Version: 4.4.0
            Status: UNCONFIRMED
          Keywords: wrong-code, alias
          Severity: normal
          Priority: P3
         Component: tree-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: rguenth at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37869