On Thu, Oct 12, 2017 at 4:40 AM, Martin Liška <mli...@suse.cz> wrote:
> On 10/11/2017 04:59 PM, Jason Merrill wrote:
>> On Thu, Oct 5, 2017 at 12:53 PM, Martin Liška <mli...@suse.cz> wrote:
>>> On 10/05/2017 05:07 PM, Jason Merrill wrote:
>>>> On Thu, Oct 5, 2017 at 6:31 AM, Martin Liška <mli...@suse.cz> wrote:
>>>>> As discussed 2 days ago on IRC with Jakub and Jonathan, C++ standard says
>>>>> that having a non-return
>>>>> function with missing return statement is undefined behavior. We've got
>>>>> -fsanitize=return check for
>>>>> that and we can in such case instrument __builtin_unreachable(). This
>>>>> patch does that.
>>>>
>>>>
>>>> Great.
>>>>
>>>>> And there's still some fallout:
>>>>>
>>>>> FAIL: g++.dg/cpp0x/constexpr-diag3.C -std=c++11 (test for errors, line
>>>>> 7)
>>>>> FAIL: g++.dg/cpp0x/constexpr-neg3.C -std=c++11 (test for errors, line
>>>>> 12)
>>>>> FAIL: g++.dg/cpp1y/constexpr-return2.C -std=c++14 (test for errors,
>>>>> line 7)
>>>>> FAIL: g++.dg/cpp1y/constexpr-return2.C -std=c++14 (test for excess
>>>>> errors)
>>>>> FAIL: g++.dg/cpp1y/pr63996.C -std=c++14 (test for errors, line 9)
>>>>> FAIL: g++.dg/cpp1y/pr63996.C -std=c++14 (test for excess errors)
>>>>>
>>>>> 1) there are causing:
>>>>>
>>>>> ./xg++ -B.
>>>>> /home/marxin/Programming/gcc/gcc/testsuite/g++.dg/cpp1y/pr63996.C
>>>>> /home/marxin/Programming/gcc/gcc/testsuite/g++.dg/cpp1y/pr63996.C:9:23:
>>>>> in constexpr expansion of ‘foo(1)’
>>>>> /home/marxin/Programming/gcc/gcc/testsuite/g++.dg/cpp1y/pr63996.C:4:1:
>>>>> error: ‘__builtin_unreachable()’ is not a constant expression
>>>>> foo (int i)
>>>>> ^~~
>>>>>
>>>>> Where we probably should not emit the built-in call. Am I right?
>>>>
>>>>
>>>> Or constexpr.c could give a more friendly diagnostic for
>>>> __builtin_unreachable. It's correct to give a diagnostic here for
>>>> this testcase.
>>>
>>>
>>> Hi.
>>>
>>> That's good idea, any suggestion different from:
>>>
>>> ./xg++ -B.
>>> /home/marxin/Programming/gcc2/gcc/testsuite/g++.dg/cpp1y/pr63996.C
>>> /home/marxin/Programming/gcc2/gcc/testsuite/g++.dg/cpp1y/pr63996.C:9:23:
>>> in constexpr expansion of ‘foo(1)’
>>> <built-in>: error: constexpr can't contain call of a non-return function
>>> ‘__builtin_unreachable’
>>>
>>> which is probably misleading as it points to a function call that is
>>> actually missing in source code.
>>> Should we distinguish between implicit and explicit __builtin_unreachable?
>>
>> Probably without your change the constexpr code already diagnoses the
>> missing return as "constexpr call flows off the end of the function";
>> that same message seems appropriate.
>
> Hello.
>
> Ok, I've done that. Sending patch candidate.
>
>>
>>> So turning on the warning by default for c++, we get about 500 failing
>>> test-cases. Uf :/
>>
>> Yes, we've been sloppy about this in the testsuite. :(
>
> I'll fix it. For being sure, I'm sending first part where I demonstrate how I
> plan to change
> tests, with following preference:
>
> 1) change function to void type if possible
> 2) return a default value for functions not returning a value (for complex
> return value of a type A:
> I do { static A a; return a; } is it appropriate?
How about "return A();" ?
Jason
