On 3/5/19 3:40 PM, Jakub Jelinek wrote:
> On Tue, Mar 05, 2019 at 05:33:45PM -0500, Jason Merrill wrote:
>> The x86_64 psABI says that an empty class isn't passed or returned in memory
>> or registers, so we shouldn't set %eax in this function. This seems like a
>> missed case from the GCC 8 TYPE_EMPTY_P changes.
>>
>> Shall I apply this for GCC 9, or hold it for stage 1?
>>
>> * function.c (expand_function_end): Don't copy a TYPE_EMPTY_P
>> result.
>
> I'd go for it now. See below for a testsuite nit:
Agreed.
>
>> --- /dev/null
>> +++ b/gcc/testsuite/g++.dg/opt/empty3.C
>> @@ -0,0 +1,8 @@
>> +// PR c++/88529
>> +// { dg-do compile { target c++11 } }
>> +// { dg-final { scan-assembler-not mov { target x86_64-*-* } } }
>
> But this probably needs to be { target { { i?86-*-* x86_64-*-* } && { ! {
> ia32 } } } }
> or similar instead, so that it is done for x86_64 -m64 and -mx32, but not
> -m32.
>
>> +// The x86_64 psABI says that f() doesn't put the return value anywhere.
>> +
>> +class A{};
>> +
>> +A f() { return {}; }
>
> Jakub
>
