On Wed, Oct 9, 2013 at 6:23 PM, Richard Henderson <r...@redhat.com> wrote:
> This doesn't seem right at all.
>
> The bug is that I gets set to UINT64_MAX, right? Where's the
> incorrect conversion from int to __int128_t? Surely you can
Please see Comment #5 of PR58542:
--cut here--
The problem actually starts in expand_atomic_compare_and_swap, in:
(gdb) list
7339 create_convert_operand_to (&ops[3], expected, mode, true);
7340 create_convert_operand_to (&ops[4], desired, mode, true);
7341 create_integer_operand (&ops[5], is_weak);
7342 create_integer_operand (&ops[6], succ_model);
7343 create_integer_operand (&ops[7], fail_model);
7344 expand_insn (icode, 8, ops);
ops[4] is converted in unsigned mode, so from "desired" operand:
(gdb) p debug_rtx (desired)
(const_int -1 [0xffffffffffffffff])
we got:
(gdb) p ops[4]
$45 = {type = EXPAND_CONVERT_TO, unsigned_p = 1, unused = 0, mode =
TImode, value = 0x7fffeffc21e0}
(gdb) p debug_rtx (ops[4].value)
(const_double -1 [0xffffffffffffffff] 0 [0] 0 [0] 0 [0])
So, it is actually expansion of atomic_compare_and_swap, which doesn't
account for signedness of "desired" operand.
Manually changing the argument from "true" to "false" for ops[4]
generates correct code.
--cut here--
> produce a reduced test case that doesn't involve all of <atomic>
> to show that.
I did try, but without necessary c++ expertise, I was not able to
create equivalent c testcase.
Uros.
