procyberian/gcc
1
0
Fork 0
Code Issues Pull requests Projects Releases Packages Wiki Activity Actions

c++: unsynthesized defaulted constexpr fn [PR110122]

Browse source 
In this other testcase from PR110122, during regeneration of the generic
lambda with V=Bar{}, substitution followed by coerce_template_parms for
A<V>'s template argument naturally yields a copy of V in terms of Bar's
(implicitly) defaulted copy constructor.

This however happens inside a template context so although we introduced
a use of the copy constructor, mark_used didn't actually synthesize it,
which causes subsequent constant evaluation of the template argument to
fail with:

  nontype-class59.C: In instantiation of ‘void f() [with Bar V = Bar{Foo()}]’:
  nontype-class59.C:22:11:   required from here
  nontype-class59.C:18:18: error: ‘constexpr Bar::Bar(const Bar&)’ used before its definition

We already make sure to instantiate templated constexpr functions needed
for constant evaluation (as per P0859R0).  So this patch fixes this by
making us synthesize defaulted constexpr functions needed for constant
evaluation as well.

	PR c++/110122

gcc/cp/ChangeLog:

	* constexpr.cc (cxx_eval_call_expression): Synthesize defaulted
	functions needed for constant evaluation.
	(instantiate_cx_fn_r): Likewise.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp2a/nontype-class59.C: New test.
This commit is contained in:
Patrick Palka 2023-06-11 11:27:10 -04:00
parent 682d401a6b
commit 59946a4c0c
2 changed files with 33 additions and 4 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

14
gcc/cp/constexpr.cc
View file

@ -2897,7 +2897,7 @@ cxx_eval_call_expression (const constexpr_ctx *ctx, tree t,
/* We can't defer instantiating the function any longer. */
if (!DECL_INITIAL (fun)
&& DECL_TEMPLOID_INSTANTIATION (fun)
&& (DECL_TEMPLOID_INSTANTIATION (fun) || DECL_DEFAULTED_FN (fun))
&& !uid_sensitive_constexpr_evaluation_p ())
{
location_t save_loc = input_location;
@ -2905,7 +2905,10 @@ cxx_eval_call_expression (const constexpr_ctx *ctx, tree t,
++function_depth;
if (ctx->manifestly_const_eval == mce_true)
FNDECL_MANIFESTLY_CONST_EVALUATED (fun) = true;
instantiate_decl (fun, /*defer_ok*/false, /*expl_inst*/false);
if (DECL_TEMPLOID_INSTANTIATION (fun))
instantiate_decl (fun, /*defer_ok*/false, /*expl_inst*/false);
else
synthesize_method (fun);
--function_depth;
input_location = save_loc;
}
@ -8110,11 +8113,14 @@ instantiate_cx_fn_r (tree *tp, int *walk_subtrees, void */*data*/)
&& DECL_DECLARED_CONSTEXPR_P (*tp)
&& !DECL_INITIAL (*tp)
&& !trivial_fn_p (*tp)
&& DECL_TEMPLOID_INSTANTIATION (*tp)
&& (DECL_TEMPLOID_INSTANTIATION (*tp) || DECL_DEFAULTED_FN (*tp))
&& !uid_sensitive_constexpr_evaluation_p ())
{
++function_depth;
instantiate_decl (*tp, /*defer_ok*/false, /*expl_inst*/false);
if (DECL_TEMPLOID_INSTANTIATION (*tp))
instantiate_decl (*tp, /*defer_ok*/false, /*expl_inst*/false);
else
synthesize_method (*tp);
--function_depth;
}
else if (TREE_CODE (*tp) == CALL_EXPR

23
gcc/testsuite/g++.dg/cpp2a/nontype-class59.C Normal file
View file

@ -0,0 +1,23 @@
// PR c++/110122
// { dg-do compile { target c++20 } }
struct Foo {
Foo() = default;
constexpr Foo(const Foo&) { }
};
struct Bar {
Foo _;
};
template<Bar V>
struct A { };
template<Bar V>
void f() {
[](auto){ A<V> d; }(0); // { dg-bogus "used before its definition" }
};
int main() {
f<Bar{}>();
}