Re: PING^1: [PATCH] Add TYPE_EMPTY_RECORD for C++ empty class

[Jakub Jelinek]

On Tue, Jan 26, 2016 at 01:21:52PM -0800, H.J. Lu wrote:
> Like this:
> 
> /* Returns true if TYPE is POD for the purpose of layout and an empty
>    class or an class with empty classes.  */
> 
> static bool
> is_empty_record (tree type)
> {
>   if (type == error_mark_node)
>     return false;
> 
>   if (!CLASS_TYPE_P (type))
>     return false;
> 
>   if (CLASSTYPE_NON_LAYOUT_POD_P (type))
>     return false;
> 
>   gcc_assert (COMPLETE_TYPE_P (type));
> 
>   if (CLASSTYPE_EMPTY_P (type))
>     return true;
> 
>   tree field;
> 
>   for (field = TYPE_FIELDS (type); field; field = DECL_CHAIN (field))
>     if (TREE_CODE (field) == FIELD_DECL
>         && !DECL_ARTIFICIAL (field)
>         && !is_empty_record (TREE_TYPE (field)))
>       return false;
> 
>   return true;
> }

So you say that K1 in e.g.:

struct A1 {}; struct A2 {};
struct B1 { A1 a; A2 b; }; struct B2 { A1 a; A2 b; };
struct C1 { B1 a; B2 b; }; struct C2 { B1 a; B2 b; };
struct D1 { C1 a; C2 b; }; struct D2 { C1 a; C2 b; };
struct E1 { D1 a; D2 b; }; struct E2 { D1 a; D2 b; };
struct F1 { E1 a; E2 b; }; struct F2 { E1 a; E2 b; };
struct G1 { F1 a; F2 b; }; struct G2 { F1 a; F2 b; };
struct H1 { G1 a; G2 b; }; struct H2 { G1 a; G2 b; };
struct I1 { H1 a; H2 b; }; struct I2 { H1 a; H2 b; };
struct J1 { I1 a; I2 b; }; struct J2 { I1 a; I2 b; };
struct K1 { J1 a; J2 b; };
int v;
__attribute__((noinline, noclone))
K1 foo (int a, K1 x, int b)
{
  v = a + b;
  return x;
}
K1 k, m;
void
bar (void)
{
  m = foo (1, k, 2);
}

is empty class?  What does clang do with this?

        Jakub