On Thu, 3 Feb 2022, Jason Merrill wrote:
> On 2/3/22 16:06, Patrick Palka wrote:
> > On Thu, 3 Feb 2022, Jason Merrill wrote:
> >
> > > On 2/3/22 14:58, Patrick Palka wrote:
> > > > When synthesizing a defaulted comparison op from
> > > > maybe_instantiate_noexcept, we seem to be forgetting to instantiate the
> > > > noexcept-spec afterwards.
> > >
> > > Hmm, there shouldn't be any need to instantiate the noexcept-spec
> > > afterwards,
> > > it should have been set by ~comp_info.
> >
> > It appears the comp_info class sets the noexcept-spec only if the
> > comparison function hasn't been declared with an explicit noexcept-spec.
> > Otherwise the class doesn't touch the noexcept-spec, and it remains a
> > DEFERRED_NOEXCEPT with non-NULL DEFERRED_NOEXCEPT_PATTERN.
>
> Ah, I see. So perhaps we should entirely skip the current DECL_MAYBE_DELETED
> handling in maybe_instantiate_noexcept if we have DEFERRED_NOEXCEPT with
> non-null DEFERRED_NOEXCEPT_PATTERN (which seems to want another macro)?
Hmm, I tried something to that effect but it looks like mark_used relies
solely on the DECL_MAYBE_DELETED handling in maybe_instantiate_noexcept
to determine deletedness of a defaulted comparison operator (via trying
to synthesize it). So by sometimes sidestepping this handling, we end
up failing to diagnose the use of the deleted defaulted <=> in e.g.:
#include <compare>
struct A { };
template<bool B>
struct X {
auto operator<=>(const X&) const noexcept(B) = default;
A a;
};
X<true> x_t;
auto c = x_t <=> x_t; // should be error: use of deleted <=> b/c A lacks <=>
In light of this, I suppose mark_used should directly perform
DECL_MAYBE_DELETED synthesization of its own?
And it looks like DECL_MAYBE_DELETED is always false after doing
maybe_synthesize_method, so I think maybe_instantiate_noexcept should
return !DECL_DELETED_FN instead of !DECL_MAYBE_DELETED after synthesization.
How does this look? Lightly tested so far, bootstrap and regtesting in
progress.
-- >8 --
PR c++/96242
gcc/cp/ChangeLog:
* decl2.cc (mark_used): Directly synthesize a DECL_MAYBE_DELETED
fn by calling maybe_synthesize_method instead of relying on
maybe_instantiate_noexcept.
* pt.cc (maybe_instantiate_noexcept): Restrict DECL_MAYBE_DELETED
synthesization to only fns with an implicit noexcept-spec, and
return !DECL_DELETED_FN instead of !DECL_MAYBE_DELETED afteward.
gcc/testsuite/ChangeLog:
* g++.dg/cpp2a/spaceship-synth15.C: New test.
---
gcc/cp/decl2.cc | 17 ++++++++++----
gcc/cp/pt.cc | 11 +++++-----
.../g++.dg/cpp2a/spaceship-synth15.C | 22 +++++++++++++++++++
3 files changed, 41 insertions(+), 9 deletions(-)
create mode 100644 gcc/testsuite/g++.dg/cpp2a/spaceship-synth15.C
diff --git a/gcc/cp/decl2.cc b/gcc/cp/decl2.cc
index a2aa5f1de4e..4d3798d02fe 100644
--- a/gcc/cp/decl2.cc
+++ b/gcc/cp/decl2.cc
@@ -5772,10 +5772,19 @@ mark_used (tree decl, tsubst_flags_t complain)
if (TREE_CODE (decl) == CONST_DECL)
used_types_insert (DECL_CONTEXT (decl));
- if (TREE_CODE (decl) == FUNCTION_DECL
- && !DECL_DELETED_FN (decl)
- && !maybe_instantiate_noexcept (decl, complain))
- return false;
+ if (TREE_CODE (decl) == FUNCTION_DECL)
+ {
+ if (DECL_MAYBE_DELETED (decl))
+ {
+ ++function_depth;
+ maybe_synthesize_method (decl);
+ --function_depth;
+ }
+
+ if (!DECL_DELETED_FN (decl)
+ && !maybe_instantiate_noexcept (decl, complain))
+ return false;
+ }
if (TREE_CODE (decl) == FUNCTION_DECL
&& DECL_DELETED_FN (decl))
diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index d219bba6ac1..584c752529b 100644
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -25982,7 +25982,11 @@ maybe_instantiate_noexcept (tree fn, tsubst_flags_t
complain)
&& (!flag_noexcept_type || type_dependent_expression_p (fn)))
return true;
- if (DECL_MAYBE_DELETED (fn))
+ tree fntype = TREE_TYPE (fn);
+ tree spec = TYPE_RAISES_EXCEPTIONS (fntype);
+
+ if (DECL_MAYBE_DELETED (fn)
+ && (!spec || UNEVALUATED_NOEXCEPT_SPEC_P (spec)))
{
if (fn == current_function_decl)
/* We're in start_preparsed_function, keep going. */
@@ -25991,12 +25995,9 @@ maybe_instantiate_noexcept (tree fn, tsubst_flags_t
complain)
++function_depth;
maybe_synthesize_method (fn);
--function_depth;
- return !DECL_MAYBE_DELETED (fn);
+ return !DECL_DELETED_FN (fn);
}
- tree fntype = TREE_TYPE (fn);
- tree spec = TYPE_RAISES_EXCEPTIONS (fntype);
-
if (!spec || !TREE_PURPOSE (spec))
return true;
diff --git a/gcc/testsuite/g++.dg/cpp2a/spaceship-synth15.C
b/gcc/testsuite/g++.dg/cpp2a/spaceship-synth15.C
new file mode 100644
index 00000000000..00ea6c10474
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/spaceship-synth15.C
@@ -0,0 +1,22 @@
+// PR c++/96242
+// { dg-do compile { target c++20 } }
+
+#include <compare>
+
+template<bool B>
+struct X {
+ auto operator<=>(const X&) const noexcept(B) = default;
+ bool operator==(const X&) const noexcept(!B) = default;
+};
+
+X<true> x_t;
+static_assert(noexcept(x_t <=> x_t));
+static_assert(noexcept(x_t < x_t));
+static_assert(!noexcept(x_t == x_t));
+static_assert(!noexcept(x_t != x_t));
+
+X<false> x_f;
+static_assert(!noexcept(x_f <=> x_f));
+static_assert(!noexcept(x_f < x_f));
+static_assert(noexcept(x_f == x_f));
+static_assert(noexcept(x_f != x_f));
--
2.35.0
