Re: [RFC] Bare bones of virtual call tracking

[Xinliang David Li <davidxl at google dot com>]

Some suggestions for the future:

1) add summary info in the odr dump -- i.e. for each node, dump the
number of direct bases, direct subtypes, number of all bases, all
subtypes;
2) add statistics dump -- average size of  a hierarchy subgraph

3) Dump the graph using top-order -- starting from roots of each sub-graph;
4) Add VCG dump per-hierarchy.

thanks,

David


On Thu, Aug 15, 2013 at 9:17 AM, Jan Hubicka <hubicka@ucw.cz> wrote:
>> On 08/14/2013 02:14 AM, Jan Hubicka wrote:
>> >As a temporary hack I suppose I can rely on assembler name of virtual table
>> >to be unique for each templated class?
>>
>> Actually, that seems like a fine solution for devirtualization; just
>> compare the mangled name of the vtable to establish type identity.
> OK,
> does this seem to make sense?  I checked that it gets rid of my
> false ODR violation warnings (I disabled the code for types not
> having virtual tables).
>
> So if it looks OK, I would like to go ahead with this patch.
> (I am testing it now in isolation at x86_64-linux).
>
> Honza
>
> Index: tree.c
> ===================================================================
> --- tree.c      (revision 201764)
> +++ tree.c      (working copy)
> @@ -11833,15 +11833,15 @@ types_same_for_odr (tree type1, tree typ
>    if (type1 == type2)
>      return true;
>
> -  /* If types are not structuraly same, do not bother to contnue.
> -     Match in the remainder of code would mean ODR violation.  */
> -  if (!types_compatible_p (type1, type2))
> -    return false;
> -
> +  /* Without LTO main variants of types are unique.  */
>  #ifndef ENABLE_CHECKING
>    if (!in_lto_p)
>      return false;
>  #endif
> +   /* If types are not structuraly same, do not bother to contnue.
> +      Match in the remainder of code would mean ODR violation.  */
> +   if (!types_compatible_p (type1, type2))
> +     return false;
>
>    /* Check for anonymous namespaces. Those have !TREE_PUBLIC
>       on the corresponding TYPE_STUB_DECL.  */
> @@ -11852,6 +11852,34 @@ types_same_for_odr (tree type1, tree typ
>           || !TREE_PUBLIC (TYPE_STUB_DECL (type2))))
>      return false;
>
> +  /* When assembler name of virtual table is available, it is
> +     easy to compare types for equivalence.
> +     FIXME: the code bellow consider all instantiations of the same
> +     template to have same name.  This is because we have no access
> +     to template parameters.
> +     To avoid false positives that may lead to wrong devirtualizations,
> +     compoare also representative virtual tables.
> +     We can still return false positive positives for types without
> +     virtual tables, but for the moment we do not care.  */
> +  if (TYPE_BINFO (type1) && TYPE_BINFO (type2)
> +      && BINFO_VTABLE (TYPE_BINFO (type1))
> +      && BINFO_VTABLE (TYPE_BINFO (type2)))
> +    {
> +      tree v1 = BINFO_VTABLE (TYPE_BINFO (type1));
> +      tree v2 = BINFO_VTABLE (TYPE_BINFO (type2));
> +
> +      if (TREE_CODE (v1) == POINTER_PLUS_EXPR)
> +       {
> +         if (TREE_CODE (v2) != POINTER_PLUS_EXPR
> +             || !operand_equal_p (TREE_OPERAND (v1, 1),
> +                                  TREE_OPERAND (v2, 1), 0))
> +           return false;
> +         v1 = TREE_OPERAND (TREE_OPERAND (v1, 0), 0);
> +         v2 = TREE_OPERAND (TREE_OPERAND (v2, 0), 0);
> +       }
> +      return DECL_ASSEMBLER_NAME (v1) == DECL_ASSEMBLER_NAME (v2);
> +    }
> +
>    if (!TYPE_NAME (type1))
>      return false;
>    if (!decls_same_for_odr (TYPE_NAME (type1), TYPE_NAME (type2)))