On 03/16/2016 08:38 AM, H.J. Lu wrote:
> FAIL: g++.dg/abi/pr60336-1.C   scan-assembler jmp[\t ]+[^$]*?_Z3xxx9true_type
> FAIL: g++.dg/abi/pr60336-5.C   scan-assembler jmp[\t ]+[^$]*?_Z3xxx9true_type
> FAIL: g++.dg/abi/pr60336-6.C   scan-assembler jmp[\t ]+[^$]*?_Z3xxx9true_type
> FAIL: g++.dg/abi/pr60336-7.C   scan-assembler jmp[\t ]+[^$]*?_Z3xxx9true_type
> FAIL: g++.dg/abi/pr60336-9.C   scan-assembler jmp[\t ]+[^$]*?_Z3xxx9true_type
> FAIL: g++.dg/abi/pr68355.C   scan-assembler jmp[\t
> ]+[^$]*?_Z3xxx17integral_constantIbLb1EE

These pass for me on x86_64, but I do see calls with -m32.

> They are expected since get_ref_base_and_extent needs to be
> changed to set bitsize to 0 for empty types so that when
> ref_maybe_used_by_call_p_1 calls get_ref_base_and_extent to
> get 0 as the maximum size on empty type.  Otherwise, find_tail_calls
> won't perform tail call optimization for functions with empty type
> parameters.

That isn't why the optimization isn't happening in pr68355 with -m32; 
the .optimized dump has

   xxx (D.2289); [tail call]

Rather, the failure seems to happen in load_register_parameter, at

>               /* Check for overlap with already clobbered argument area,
>                  providing that this has non-zero size.  */
>               if (is_sibcall
>                   && (size == 0
>                       || mem_overlaps_already_clobbered_arg_p
>                                            (XEXP (args[i].value, 0), size)))
>                 *sibcall_failure = 1;

The code seems to contradict the comment, and seems to have been broken 
by r162402.  Applying this additional patch fixes those tests.