On Thu, Dec 18, 2025 at 11:03:12AM +0700, Jason Merrill wrote:
> On 12/16/25 6:34 PM, Nathaniel Shead wrote:
> > Here's attempt two at this patch, with a testcase for the linker issue
> > I'd inadvertantly caused with my previous attempt.
> >
> > Bootstrapped and regtested on x86_64-pc-linux-gnu, OK for trunk?
> >
> > -- >8 --
> >
> > Modules allow temploid friends to no longer be implicitly inline, as
> > functions defined in a class body will not be implicitly inline if
> > attached to a named module.
> >
> > This requires us to clean up linkage handling a little bit, mostly by
> > replacing usages of 'DECL_TEMPLATE_INSTANTIATION' with
> > 'DECL_TEMPLOID_INSTANTIATION' when determining if an entity has vague
> > linkage.
> >
> > This caused the friend88.C testcase to miscompile however, as 'foo' was
> > incorrectly having 'DECL_FRIEND_PSEUDO_TEMPLATE_INSTANTIATION' getting
> > set because it was keeping its tinfo.
> >
> > This is because 'non_templated_friend_p' was returning 'false', since
> > the function didn't have a primary template. But that's expected I
> > think here, so fixed by also returning true for friend declarations
> > pushed into namespace scope, which still allows dependent nested friends
> > to be considered templated.
>
> Will that wrongly return true for a friend namespace-scope template? The
> test should check that case.
It does not; in cases like
template <typename T> friend void namespace_scope();
this is a primary template and so primary is non-null anyway, and
'primary != tmpl' returns false. I'm not sure how to test this though,
as the test I've been using here only works because the affected
functions should not be comdat, but for a function template it should be
comdat anyway. And this would not be a pseudo template instantiation
regardless, as it's actually a template.
> It seems like a bug that TPARMS_PRIMARY_TEMPLATE would ever be null.
Assuming this is about 'template <class T> friend A<T>::f()', this
appears to be deliberate from this hunk in push_template_decl added
in r0-76180-gc9cbfca6 (PR c++/27714):
bool is_primary = false;
if (is_friend && ctx
&& uses_template_parms_level (ctx, current_template_depth))
/* A friend template that specifies a class context, i.e.
template <typename T> friend void A<T>::f();
is not primary. */
;
And indeed removing this causes redeclaration errors. I'm not sure how
(or indeed, if it would be sensible) to change this.
> > PR c++/122819
> >
> > gcc/cp/ChangeLog:
> >
> > * decl.cc (start_preparsed_function): Use
> > DECL_TEMPLOID_INSTANTIATION instead of
> > DECL_TEMPLATE_INSTANTIATION to check vague linkage.
> > * decl2.cc (vague_linkage_p): Likewise.
> > (c_parse_final_cleanups): Simplify condition.
> > * pt.cc (non_templated_friend_p): Namespace-scope friend
> > function declarations without a primary template are still
> > non-templated.
> > * semantics.cc (expand_or_defer_fn_1): Also check for temploid
> > friend functions.
> >
> > gcc/testsuite/ChangeLog:
> >
> > * g++.dg/modules/tpl-friend-22.C: New test.
> > * g++.dg/template/friend88: New test.
> >
> > Signed-off-by: Nathaniel Shead <[email protected]>
> > ---
> > gcc/cp/decl.cc | 6 ++--
> > gcc/cp/decl2.cc | 5 ++-
> > gcc/cp/pt.cc | 2 +-
> > gcc/cp/semantics.cc | 4 ++-
> > gcc/testsuite/g++.dg/modules/tpl-friend-22.C | 24 +++++++++++++++
> > gcc/testsuite/g++.dg/template/friend88.C | 32 ++++++++++++++++++++
> > 6 files changed, 65 insertions(+), 8 deletions(-)
> > create mode 100644 gcc/testsuite/g++.dg/modules/tpl-friend-22.C
> > create mode 100644 gcc/testsuite/g++.dg/template/friend88.C
> >
> > diff --git a/gcc/cp/decl.cc b/gcc/cp/decl.cc
> > index 74c862ec1c7..31081b390fa 100644
> > --- a/gcc/cp/decl.cc
> > +++ b/gcc/cp/decl.cc
> > @@ -19750,7 +19750,7 @@ start_preparsed_function (tree decl1, tree attrs,
> > int flags)
> > }
> > }
> > - bool honor_interface = (!DECL_TEMPLATE_INSTANTIATION (decl1)
> > + bool honor_interface = (!DECL_TEMPLOID_INSTANTIATION (decl1)
> > /* Implicitly-defined methods (like the
> > destructor for a class in which no destructor
> > is explicitly declared) must not be defined
> > @@ -19781,7 +19781,7 @@ start_preparsed_function (tree decl1, tree attrs,
> > int flags)
> > else if (!finfo->interface_unknown && honor_interface)
> > {
> > if (DECL_DECLARED_INLINE_P (decl1)
> > - || DECL_TEMPLATE_INSTANTIATION (decl1))
> > + || DECL_TEMPLOID_INSTANTIATION (decl1))
> > {
> > DECL_EXTERNAL (decl1)
> > = (finfo->interface_only
> > @@ -19823,7 +19823,7 @@ start_preparsed_function (tree decl1, tree attrs,
> > int flags)
> > DECL_EXTERNAL (decl1) = 0;
> > if ((DECL_DECLARED_INLINE_P (decl1)
> > - || DECL_TEMPLATE_INSTANTIATION (decl1))
> > + || DECL_TEMPLOID_INSTANTIATION (decl1))
> > && ! DECL_INTERFACE_KNOWN (decl1))
> > DECL_DEFER_OUTPUT (decl1) = 1;
> > else
> > diff --git a/gcc/cp/decl2.cc b/gcc/cp/decl2.cc
> > index 8ec9740c8a9..01bf26b1e4f 100644
> > --- a/gcc/cp/decl2.cc
> > +++ b/gcc/cp/decl2.cc
> > @@ -2510,7 +2510,7 @@ vague_linkage_p (tree decl)
> > || (TREE_CODE (decl) == FUNCTION_DECL
> > && DECL_DECLARED_INLINE_P (decl))
> > || (DECL_LANG_SPECIFIC (decl)
> > - && DECL_TEMPLATE_INSTANTIATION (decl))
> > + && DECL_TEMPLOID_INSTANTIATION (decl))
> > || (VAR_P (decl) && DECL_INLINE_VAR_P (decl)))
> > return true;
> > else if (DECL_FUNCTION_SCOPE_P (decl))
> > @@ -5850,8 +5850,7 @@ c_parse_final_cleanups (void)
> > && !(header_module_p ()
> > && (DECL_DEFAULTED_FN (decl) || decl_tls_wrapper_p (decl)))
> > /* Don't complain if the template was defined. */
> > - && !((DECL_TEMPLATE_INSTANTIATION (decl)
> > - || DECL_FRIEND_PSEUDO_TEMPLATE_INSTANTIATION (decl))
> > + && !(DECL_TEMPLOID_INSTANTIATION (decl)
> > && DECL_INITIAL (DECL_TEMPLATE_RESULT
> > (template_for_substitution (decl))))
> > && warning_at (DECL_SOURCE_LOCATION (decl), 0,
> > diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
> > index 341e5ab8808..b37de8723ce 100644
> > --- a/gcc/cp/pt.cc
> > +++ b/gcc/cp/pt.cc
> > @@ -11652,7 +11652,7 @@ non_templated_friend_p (tree t)
> > template <class T> friend A<T>::f(); */
> > tree tmpl = TI_TEMPLATE (ti);
> > tree primary = DECL_PRIMARY_TEMPLATE (tmpl);
> > - return (primary && primary != tmpl);
> > + return ((primary || DECL_NAMESPACE_SCOPE_P (t)) && primary != tmpl);
> > }
> > else
> > return false;
> > diff --git a/gcc/cp/semantics.cc b/gcc/cp/semantics.cc
> > index e420fd4ebaf..02a1e6aee0e 100644
> > --- a/gcc/cp/semantics.cc
> > +++ b/gcc/cp/semantics.cc
> > @@ -5537,7 +5537,9 @@ expand_or_defer_fn_1 (tree fn)
> > of the compilation. Until that point, we do not want the back
> > end to output them -- but we do want it to see the bodies of
> > these functions so that it can inline them as appropriate. */
> > - if (DECL_DECLARED_INLINE_P (fn) || DECL_IMPLICIT_INSTANTIATION (fn))
> > + if (DECL_DECLARED_INLINE_P (fn)
> > + || DECL_IMPLICIT_INSTANTIATION (fn)
> > + || DECL_FRIEND_PSEUDO_TEMPLATE_INSTANTIATION (fn))
> > {
> > if (DECL_INTERFACE_KNOWN (fn))
> > /* We've already made a decision as to how this function will
> > diff --git a/gcc/testsuite/g++.dg/modules/tpl-friend-22.C
> > b/gcc/testsuite/g++.dg/modules/tpl-friend-22.C
> > new file mode 100644
> > index 00000000000..a77d1cbecad
> > --- /dev/null
> > +++ b/gcc/testsuite/g++.dg/modules/tpl-friend-22.C
> > @@ -0,0 +1,24 @@
> > +// PR c++/122819
> > +// { dg-do compile { target *-*-*gnu* } }
> > +// { dg-additional-options "-fmodules" }
> > +
> > +export module M;
> > +
> > +template <typename T> struct S;
> > +void foo(S<float>);
> > +
> > +template <typename T> struct S {
> > + friend void foo(S) {}
> > +};
> > +
> > +void foo(S<double>);
> > +
> > +void use() {
> > + foo(S<int>{});
> > + foo(S<float>{});
> > + foo(S<double>{});
> > +}
> > +
> > +// { dg-final { scan-assembler "_ZW1M3fooS_1SIiE,comdat" } }
> > +// { dg-final { scan-assembler "_ZW1M3fooS_1SIfE,comdat" } }
> > +// { dg-final { scan-assembler "_ZW1M3fooS_1SIdE,comdat" } }
> > diff --git a/gcc/testsuite/g++.dg/template/friend88.C
> > b/gcc/testsuite/g++.dg/template/friend88.C
> > new file mode 100644
> > index 00000000000..73d3d525900
> > --- /dev/null
> > +++ b/gcc/testsuite/g++.dg/template/friend88.C
> > @@ -0,0 +1,32 @@
> > +// PR c++/122819
> > +// { dg-do compile { target c++11 } }
> > +
> > +template <typename T> struct basic_streambuf;
> > +using streambuf = basic_streambuf<char>;
> > +
> > +struct S {
> > + void foo();
> > + template <typename T> void bar();
> > +};
> > +
> > +template <typename T> struct X {
> > + void foo();
> > +};
> > +
> > +template <typename T> struct basic_streambuf {
> > + void qux();
> > +
> > + friend void foo();
> > + friend void S::foo();
> > + template <typename U> friend void S::bar();
> > + template <typename U> friend void X<U>::foo();
> > + template <typename U> friend void basic_streambuf<U>::qux();
> > +};
> > +extern template struct basic_streambuf<char>;
> > +
> > +void foo() {}
> > +void S::foo() {}
> > +
> > +// { dg-final { scan-assembler {_Z3foov:} } }
> > +// { dg-final { scan-assembler {_ZN1S3fooEv:} } }
> > +// { dg-final { scan-assembler-not {comdat} } }
>
