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. > 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. :( Jason
