On Thu, 9 Mar 2023, Jason Merrill wrote: > On 3/9/23 14:32, Patrick Palka wrote: > > On Mon, 6 Mar 2023, Marek Polacek via Gcc-patches wrote: > > > > > When processing a noexcept, constructors aren't elided: build_over_call > > > has > > > /* It's unsafe to elide the constructor when handling > > > a noexcept-expression, it may evaluate to the wrong > > > value (c++/53025). */ > > > && (force_elide || cp_noexcept_operand == 0)) > > > so the assert I added recently needs to be relaxed a little bit. > > > > > > Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk? > > > > > > PR c++/109030 > > > > > > gcc/cp/ChangeLog: > > > > > > * constexpr.cc (cxx_eval_call_expression): Relax assert. > > > > > > gcc/testsuite/ChangeLog: > > > > > > * g++.dg/cpp0x/noexcept77.C: New test. > > > --- > > > gcc/cp/constexpr.cc | 6 +++++- > > > gcc/testsuite/g++.dg/cpp0x/noexcept77.C | 9 +++++++++ > > > 2 files changed, 14 insertions(+), 1 deletion(-) > > > create mode 100644 gcc/testsuite/g++.dg/cpp0x/noexcept77.C > > > > > > diff --git a/gcc/cp/constexpr.cc b/gcc/cp/constexpr.cc > > > index 364695b762c..5384d0e8e46 100644 > > > --- a/gcc/cp/constexpr.cc > > > +++ b/gcc/cp/constexpr.cc > > > @@ -2869,7 +2869,11 @@ cxx_eval_call_expression (const constexpr_ctx *ctx, > > > tree t, > > > /* We used to shortcut trivial constructor/op= here, but nowadays > > > we can only get a trivial function here with > > > -fno-elide-constructors. */ > > > - gcc_checking_assert (!trivial_fn_p (fun) || !flag_elide_constructors); > > > + gcc_checking_assert (!trivial_fn_p (fun) > > > + || !flag_elide_constructors > > > + /* We don't elide constructors when processing > > > + a noexcept-expression. */ > > > + || cp_noexcept_operand); > > > > It seems weird that we're performing constant evaluation within an > > unevaluated operand. Would it make sense to also fix this a second way > > by avoiding constant evaluation from maybe_constant_init when > > cp_unevaluated_operand && !manifestly_const_eval, like in > > maybe_constant_value? > > Sounds good.
Hmm, while working on this I noticed we currently don't reject a version of g++.dg/cpp2a/constexpr-inst1.C that list initializes an aggregate instead of int (ever since r12-4425-g1595fe44e11a96): struct A { int m; }; template<typename T> constexpr int f() { return T::value; } template<bool B, typename T> void h(decltype(A{B ? f<T>() : 0})); // was int{...} template<bool B, typename T> void h(...); void x() { h<false, int>(0); // OK? } ISTM we should instantiate f<int> here for the same reason we do in the original version of the testcase, and for that to happen we need to pass manifestly_const_eval=true in massage_init_elt. Does that seem reasonable?