On Wed, Jul 15, 2026 at 10:49:23PM -0400, Jason Merrill wrote:
maybe_instantiate_noexcept is guarded by
/* Don't instantiate a noexcept-specification from template context. */
if (processing_template_decl
&& (!flag_noexcept_type || type_dependent_expression_p (fn)))
return true;
So, shall that be
if (processing_template_decl
&& (!flag_noexcept_type
|| dependent_type_p (TREE_TYPE (fn))
|| type_dependent_expression_p (fn)))
return true;
or shall I use that check in maybe_diagnose_deallocation_noexcept_false?
operator delete has to return void, so maybe I don't need to be afraid
about undeduced_auto_decl.
I think the problem is more that calling maybe_instantiate_noexcept is wrong
here; this was not added to the list in
https://eel.is/c++draft/except#spec-13
Anyway, isn't grokfndecl too early? I mean for cases like
struct E {
static void operator delete (void *) noexcept (C) {}
static constexpr bool C = false;
};
which I should add to the testsuite. When grokfndecl is called,
TYPE_RAISES_EXCEPTION (TREE_TYPE (fn)) is
<tree_list 0x7fffe99a4f28
purpose <deferred_parse 0x7fffe99bbe70>>
and so nothing is reported.
This is only changed in fixup_deferred_exception_variants.
Or should cp_parser_class_specifier call
maybe_diagnose_deallocation_noexcept_false again if it parses it?
Yes, and in maybe_instantiate_noexcept, rather than tsubst_function_decl.
Ok, I've done it that way.
Note the disadvantage is that we don't diagnose when somebody just
instantiates template containing a deallocation method with dependent
noexcept and doesn't actually odr-use (etc., the
https://eel.is/c++draft/except#spec-13 list) the deallocation function,
but if that is ok, then this patch does that.
The testsuite now includes one case for the deferred parsing of exception
specifier (to test cp_parser_class_specifier), and cases where the
deallocation function with dependent noexcept isn't and is odr-used, and
case where a template has deallocation method with non-dependent noexcept.
2026-07-16 Jakub Jelinek <[email protected]>
PR c++/125833
* cp-tree.h: Implement C++29 P3424R2 - Deallocation Functions with
Throwing Exception Specification Are Ill-formed.
(maybe_diagnose_deallocation_noexcept_false): Declare.
* decl.cc (maybe_diagnose_deallocation_noexcept_false): New function.
(grokfndecl): Call it.
* pt.cc (maybe_instantiate_noexcept): Likewise.
* parser.cc (cp_parser_class_specifier): Likewise.
* g++.dg/cpp0x/dealloc2.C: Expect extra diagnostics in C++29.
* g++.dg/cpp29/dealloc1.C: New test.
--- gcc/cp/cp-tree.h.jj 2026-07-15 10:26:19.552203498 +0200
+++ gcc/cp/cp-tree.h 2026-07-16 14:11:24.301372159 +0200
@@ -7651,6 +7651,7 @@ extern tree start_decl (const
cp_decl
extern void start_decl_1 (tree, bool);
extern bool check_array_initializer (tree, tree, tree);
extern void omp_declare_variant_finalize (tree, tree);
+extern void maybe_diagnose_deallocation_noexcept_false (tree);
struct cp_decomp { tree decl; unsigned int count; };
extern void cp_finish_decl (tree, tree, bool, tree, int,
cp_decomp * = nullptr);
extern tree lookup_decomp_type (tree);
--- gcc/cp/decl.cc.jj 2026-07-15 10:26:19.554203473 +0200
+++ gcc/cp/decl.cc 2026-07-16 14:11:57.989947721 +0200
@@ -9430,6 +9430,25 @@ omp_declare_variant_finalize (tree decl,
}
}
+/* [basic.stc.dynamic.deallocation]/3 - A deallocation function shall not
+ have a potentially throwing exception specification. */
+
+void
+maybe_diagnose_deallocation_noexcept_false (tree decl)
+{
+ if (cxx_dialect >= cxx29
+ && DECL_NAME (decl)
+ && IDENTIFIER_NEWDEL_OP_P (DECL_NAME (decl))
+ && !IDENTIFIER_NEW_OP_P (DECL_NAME (decl)))
+ {
+ tree spec = TYPE_RAISES_EXCEPTIONS (TREE_TYPE (decl));
+ if (spec && spec == noexcept_false_spec)
+ error_at (DECL_SOURCE_LOCATION (decl),
+ "deallocation function %qD declared possibly throwing",
+ decl);
+ }
+}
+
static void cp_maybe_mangle_decomp (tree, cp_decomp *);
/* Finish processing of a declaration;
@@ -12621,6 +12640,10 @@ grokfndecl (tree ctype,
}
}
+ /* [basic.stc.dynamic.deallocation]/3 - A deallocation function shall not
+ have a potentially throwing exception specification. */
+ maybe_diagnose_deallocation_noexcept_false (decl);
+
/* Caller will do the rest of this. */
if (check < 0)
{
--- gcc/cp/pt.cc.jj 2026-07-15 10:26:19.556203447 +0200
+++ gcc/cp/pt.cc 2026-07-16 15:41:18.507170923 +0200
@@ -28802,6 +28802,10 @@ maybe_instantiate_noexcept (tree fn, tsu
if (orig_fn)
TREE_TYPE (orig_fn) = TREE_TYPE (fn);
+ /* [basic.stc.dynamic.deallocation]/3 - A deallocation function shall not
+ have a potentially throwing exception specification. */
+ maybe_diagnose_deallocation_noexcept_false (fn);
+
return true;
}
--- gcc/cp/parser.cc.jj 2026-07-15 17:41:44.777718295 +0200
+++ gcc/cp/parser.cc 2026-07-16 14:36:23.588496699 +0200
@@ -30135,6 +30135,10 @@ cp_parser_class_specifier (cp_parser* pa
/* Remove any template parameters from the symbol table. */
maybe_end_member_template_processing ();
+
+ /* [basic.stc.dynamic.deallocation]/3 - A deallocation function
+ shall not have a potentially throwing exception specification. */
+ maybe_diagnose_deallocation_noexcept_false (decl);
}
vec_safe_truncate (unparsed_noexcepts, 0);
--- gcc/testsuite/g++.dg/cpp0x/dealloc2.C.jj 2026-07-15 10:26:19.556203447 +0200
+++ gcc/testsuite/g++.dg/cpp0x/dealloc2.C 2026-07-16 14:11:24.308433550
+0200
@@ -3,6 +3,7 @@
struct A {};
void operator delete (void *, A);
void operator delete (void *, A) noexcept (false); // { dg-error "declaration
of 'void operator delete\\\(void\\\*, A\\\) noexcept \\\(false\\\)' has a different
exception specifier" }
+// { dg-error "deallocation function 'void operator delete\\\(void\\\*, A\\\)' declared
possibly throwing" "" { target c++29 } .-1 }
struct B {};
-void operator delete (void *, B) noexcept (false);
+void operator delete (void *, B) noexcept (false); // { dg-error "deallocation function
'void operator delete\\\(void\\\*, B\\\)' declared possibly throwing" "" { target
c++29 } }
void operator delete (void *, B); // { dg-error "declaration
of 'void operator delete\\\(void\\\*, B\\\) noexcept' has a different exception
specifier" }
--- gcc/testsuite/g++.dg/cpp29/dealloc1.C.jj 2026-07-16 14:11:24.308624193
+0200
+++ gcc/testsuite/g++.dg/cpp29/dealloc1.C 2026-07-16 15:26:04.013705590
+0200
@@ -0,0 +1,45 @@
+// P3424R2 - Deallocation Functions with Throwing Exception Specification Are
Ill-formed
+// { dg-do compile { target c++11 } }
+
+struct A {};
+struct B {};
+void operator delete (void *, A) noexcept (false); // { dg-error "deallocation function
'void operator delete\\\(void\\\*, A\\\)' declared possibly throwing" "" { target
c++29 } }
+void operator delete (void *, B) noexcept (false) {} // { dg-error "deallocation function
'void operator delete\\\(void\\\*, B\\\)' declared possibly throwing" "" { target
c++29 } }
+void operator delete[] (void *, A) noexcept (false); // { dg-error "deallocation function
'void operator delete \\\[\\\]\\\(void\\\*, A\\\)' declared possibly throwing" "" {
target c++29 } }
+void operator delete[] (void *, B) noexcept (false) {} // { dg-error "deallocation function
'void operator delete \\\[\\\]\\\(void\\\*, B\\\)' declared possibly throwing" "" {
target c++29 } }
+template <bool T, bool U>
+struct C {
+ static void operator delete (void *) noexcept (T); // { dg-error "deallocation function 'static
void C<T, U>::operator delete\\\(void\\\*\\\) \\\[with bool T = false; bool U = true\\\]' declared
possibly throwing" "" { target c++29 } }
+ static void operator delete[] (void *) noexcept (T); // { dg-error "deallocation function 'static
void C<T, U>::operator delete \\\[\\\]\\\(void\\\*\\\) \\\[with bool T = false; bool U = true\\\]'
declared possibly throwing" "" { target c++29 } }
+};
+template <bool T, bool U>
+struct D {
+ static void operator delete (void *) noexcept (T) {} // { dg-error "deallocation function 'static
void D<T, U>::operator delete\\\(void\\\*\\\) \\\[with bool T = false; bool U = true\\\]' declared
possibly throwing" "" { target c++29 } }
+ static void operator delete[] (void *) noexcept (T) {}// { dg-error "deallocation function
'static void D<T, U>::operator delete \\\[\\\]\\\(void\\\*\\\) \\\[with bool T = false; bool U =
true\\\]' declared possibly throwing" "" { target c++29 } }
+};
+C <false, false> a;
+C <true, false> b;
+D <false, false> c;
+D <true, false> d;
+auto e = &C <false, true>::operator delete;
+auto f = &C <true, true>::operator delete;
+auto g = &D <false, true>::operator delete;
+auto h = &D <true, true>::operator delete;
+auto i = &C <false, true>::operator delete[];
+auto j = &C <true, true>::operator delete[];
+auto k = &D <false, true>::operator delete[];
+auto l = &D <true, true>::operator delete[];
+struct E {
+ static void operator delete (void *) noexcept (C) {} // { dg-error "deallocation function
'static void E::operator delete\\\(void\\\*\\\)' declared possibly throwing" "" {
target c++29 } }
+ static constexpr bool C = false;
+};
+template <int N>
+struct F {
+ static void operator delete (void *) noexcept (false); // { dg-error "deallocation function
'static void F<N>::operator delete\\\(void\\\*\\\)' declared possibly throwing" "" {
target c++29 } }
+ static void operator delete[] (void *) noexcept (false); // { dg-error "deallocation function
'static void F<N>::operator delete \\\[\\\]\\\(void\\\*\\\)' declared possibly throwing"
"" { target c++29 } }
+};
+template <int N>
+struct G {
+ static void operator delete (void *) noexcept (false) {} // { dg-error "deallocation function
'static void G<N>::operator delete\\\(void\\\*\\\)' declared possibly throwing" "" {
target c++29 } }
+ static void operator delete[] (void *) noexcept (false) {} // { dg-error "deallocation function
'static void G<N>::operator delete \\\[\\\]\\\(void\\\*\\\)' declared possibly throwing"
"" { target c++29 } }
+};
Jakub
