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.
>
> > {
> > tree x = get_nth_callarg (t, 0);
> > if (is_this_parameter (x))
> > @@ -9182,16 +9187,11 @@ potential_constant_expression_1 (tree t, bool
> > want_rval, bool strict, bool now,
> > 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..a2f9801e11f
> > --- /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();
> > + }
> > +
> > +private:
> > + bool g() const;
> > +};
> > +
> > +template struct A<int>;
>
>
