On Wed, 3 May 2023, Jason Merrill wrote: > On 5/2/23 15:53, Patrick Palka wrote: > > on Tue, 2 May 2023, Patrick Palka wrote: > > > > > On Tue, 2 May 2023, Jason Merrill wrote: > > > > > > > On 5/1/23 15:59, Patrick Palka wrote: > > > > > Here we're incorrectly deeming the templated call a.g() inside b's > > > > > initializer as potentially constant, despite g being non-constexpr, > > > > > which leads to us wastefully instantiating the initializer ahead of > > > > > time > > > > > and triggering a bug in access checking deferral (which will get fixed > > > > > in the subsequent patch). > > > > > > > > > > This patch fixes this by calling get_fns earlier during potentiality > > > > > checking so that we also handle the templated form of a member > > > > > function > > > > > call (whose overall callee is a COMPONENT_REF) when checking if the > > > > > called > > > > > function is constexpr etc. > > > > > > > > > > PR c++/109480 > > > > > > > > > > gcc/cp/ChangeLog: > > > > > > > > > > * constexpr.cc (potential_constant_expression_1) <case > > > > > CALL_EXPR>: > > > > > Reorganize to call get_fns sooner. Remove dead store to > > > > > 'fun'. > > > > > > > > > > gcc/testsuite/ChangeLog: > > > > > > > > > > * g++.dg/cpp0x/noexcept59.C: Make e() constexpr so that the > > > > > expected "without object" diagnostic isn't replaced by a > > > > > "call to non-constexpr function" diagnostic. > > > > > * g++.dg/template/non-dependent25.C: New test. > > > > > --- > > > > > gcc/cp/constexpr.cc | 16 > > > > > ++++++++-------- > > > > > gcc/testsuite/g++.dg/cpp0x/noexcept59.C | 2 +- > > > > > gcc/testsuite/g++.dg/template/non-dependent25.C | 14 ++++++++++++++ > > > > > 3 files changed, 23 insertions(+), 9 deletions(-) > > > > > create mode 100644 gcc/testsuite/g++.dg/template/non-dependent25.C > > > > > > > > > > diff --git a/gcc/cp/constexpr.cc b/gcc/cp/constexpr.cc > > > > > index d1097764b10..29d872d0a5e 100644 > > > > > --- a/gcc/cp/constexpr.cc > > > > > +++ b/gcc/cp/constexpr.cc > > > > > @@ -9132,6 +9132,10 @@ potential_constant_expression_1 (tree t, bool > > > > > want_rval, bool strict, bool now, > > > > > if (fun && is_overloaded_fn (fun)) > > > > > { > > > > > + if (!RECUR (fun, true)) > > > > > + return false; > > > > > + fun = get_fns (fun); > > > > > + > > > > > if (TREE_CODE (fun) == FUNCTION_DECL) > > > > > { > > > > > if (builtin_valid_in_constant_expr_p (fun)) > > > > > @@ -9167,7 +9171,8 @@ potential_constant_expression_1 (tree t, bool > > > > > want_rval, bool strict, bool now, > > > > > expression the address will be folded away, so look > > > > > through it now. */ > > > > > if (DECL_NONSTATIC_MEMBER_FUNCTION_P (fun) > > > > > - && !DECL_CONSTRUCTOR_P (fun)) > > > > > + && !DECL_CONSTRUCTOR_P (fun) > > > > > + && !processing_template_decl) > > > > > > > > I don't see any rationale for this hunk? > > > > > > Now that we call get_fns earlier, we can reach this code path with a > > > templated non-static memfn call, but the code that follows assumes > > > non-templated form. > > > > > > I tried teaching it to handle the templated form too, but there's > > > apparently two different templated forms for non-static memfn calls, > > > one with a COMPONENT_REF callee and one with an ordinary BASELINK > > > callee (without a implicit object argument). In the former the implict > > > object argument is inside the COMPONENT_REF (and is a reference instead > > > of a pointer), and in the latter we don't even have an implicit object > > > argument to inspect. > > > > > > FWIW I think which form we use depends on whether we know if the called > > > function is a member of the current instantiation, e.g > > > > > > struct A { void f(); }; > > > > > > template<class T> struct B; > > > > > > template<class T> > > > struct C : B<T> { > > > void g(); > > > > > > void h() { > > > A::f(); // templated form has BASELINK callee, no object arg > > > C::g(); // templated form has COMPONENT_REF callee > > > } > > > }; > > > > > > So it seemed best to punt on templated non-static memfn calls here for > > > now and treat that as a separate enhancement. > > > > And I'm not even sure if the code path in question is necessary at all > > anymore: disabling it outright doesn't cause any regressions in the > > testsuite. > > It seems effectively equivalent to the body of the loop over the args a few > > lines later: > > If removing that hunk doesn't regress anything, let's do it. Probably that > should have happened in r13-55-ge9d2adc17d0dbe
Sounds good, here's the combined patch which I'm bootstrapping for good measure. Does it look OK for trunk if bootstrap+regtest succeeds? -- >8 -- Subject: [PATCH] c++: potentiality of templated memfn call [PR109480] Here we're incorrectly deeming the templated call a.g() inside b's initializer as potentially constant, despite g being non-constexpr, which leads to us wastefully instantiating the initializer ahead of time, which incidentally tiggers a bug in access checking deferral (to be fixed by the subsequent patch). This patch fixes this by calling get_fns earlier during CALL_EXPR potentiality checking so that we're able to extract a FUNCTION_DECL out of a templated member function call (whose overall is typically a COMPONENT_REF) and to the usual checking if the called function is constexpr etc. In passing, I noticed potential_constant_expression_1's special handling of the object argument of a non-static member function call is effectively the same as the generic argument handling a few lines later. So this patch just gets rid of this special handling; otherwise we'd have to adapt it to handle templated versions of such calls. PR c++/109480 gcc/cp/ChangeLog: * constexpr.cc (potential_constant_expression_1) <case CALL_EXPR>: Reorganize to call get_fns sooner. Remove special handling of the object argument of a non-static member function call. Remove dead store to 'fun'. gcc/testsuite/ChangeLog: * g++.dg/cpp0x/noexcept59.C: Make e() constexpr so that the expected "without object" diagnostic isn't replaced by a "call to non-constexpr function" diagnostic. * g++.dg/template/non-dependent25.C: New test. --- gcc/cp/constexpr.cc | 32 ++++--------------- gcc/testsuite/g++.dg/cpp0x/noexcept59.C | 2 +- .../g++.dg/template/non-dependent25.C | 14 ++++++++ 3 files changed, 21 insertions(+), 27 deletions(-) create mode 100644 gcc/testsuite/g++.dg/template/non-dependent25.C diff --git a/gcc/cp/constexpr.cc b/gcc/cp/constexpr.cc index d1097764b10..075339f7f62 100644 --- a/gcc/cp/constexpr.cc +++ b/gcc/cp/constexpr.cc @@ -9132,6 +9132,10 @@ potential_constant_expression_1 (tree t, bool want_rval, bool strict, bool now, if (fun && is_overloaded_fn (fun)) { + if (!RECUR (fun, true)) + return false; + fun = get_fns (fun); + if (TREE_CODE (fun) == FUNCTION_DECL) { if (builtin_valid_in_constant_expr_p (fun)) @@ -9162,36 +9166,12 @@ potential_constant_expression_1 (tree t, bool want_rval, bool strict, bool now, explain_invalid_constexpr_fn (fun); return false; } - /* A call to a non-static member function takes the address - of the object as the first argument. But in a constant - expression the address will be folded away, so look - through it now. */ - if (DECL_NONSTATIC_MEMBER_FUNCTION_P (fun) - && !DECL_CONSTRUCTOR_P (fun)) - { - tree x = get_nth_callarg (t, 0); - if (is_this_parameter (x)) - return true; - /* Don't require an immediately constant value, as - constexpr substitution might not use the value. */ - bool sub_now = false; - if (!potential_constant_expression_1 (x, rval, strict, - sub_now, fundef_p, - flags, jump_target)) - return false; - i = 1; - } - } - else - { - if (!RECUR (fun, true)) - return false; - fun = get_first_fn (fun); } + + fun = OVL_FIRST (fun); /* Skip initial arguments to base constructors. */ if (DECL_BASE_CONSTRUCTOR_P (fun)) i = num_artificial_parms_for (fun); - fun = DECL_ORIGIN (fun); } else if (fun) { diff --git a/gcc/testsuite/g++.dg/cpp0x/noexcept59.C b/gcc/testsuite/g++.dg/cpp0x/noexcept59.C index c752601ba09..1dc826d3111 100644 --- a/gcc/testsuite/g++.dg/cpp0x/noexcept59.C +++ b/gcc/testsuite/g++.dg/cpp0x/noexcept59.C @@ -3,7 +3,7 @@ template <class ...Ts> class A { - void e (); + constexpr bool e () { return true; }; bool f (int() noexcept(this->e())); // { dg-error "this" } bool g (int() noexcept(e())); // { dg-error "without object" } }; diff --git a/gcc/testsuite/g++.dg/template/non-dependent25.C b/gcc/testsuite/g++.dg/template/non-dependent25.C new file mode 100644 index 00000000000..c00e44532b0 --- /dev/null +++ b/gcc/testsuite/g++.dg/template/non-dependent25.C @@ -0,0 +1,14 @@ +// PR c++/109480 + +template<class T> +struct A { + void f() { + A<int> a; + const bool b = a.g(); // { dg-bogus "private" } + } + +private: + bool g() const; +}; + +template struct A<int>; -- 2.40.1.476.g69c786637d