On Fri, 31 Mar 2023, Patrick Palka wrote:
> On Thu, 30 Mar 2023, Jason Merrill wrote:
>
> > On 3/30/23 14:53, Patrick Palka wrote:
> > > On Wed, 29 Mar 2023, Jason Merrill wrote:
> > >
> > > > On 3/27/23 09:30, Patrick Palka wrote:
> > > > > On Thu, 23 Mar 2023, Patrick Palka wrote:
> > > > >
> > > > > > r13-995-g733a792a2b2e16 worked around the problem of FUNCTION_DECL
> > > > > > template arguments not always getting marked as odr-used by
> > > > > > redundantly
> > > > > > calling mark_used on the substituted ADDR_EXPR callee of a
> > > > > > CALL_EXPR.
> > > > > > This is just a narrow workaround however, since using a
> > > > > > FUNCTION_DECL
> > > > > > as
> > > > > > a template argument alone should constitutes an odr-use; we
> > > > > > shouldn't
> > > > > > need to subsequently e.g. call the function or take its address.
> > > >
> > > > Agreed. But why didn't we already wrap it in an ADDR_EXPR? Even for
> > > > reference tparms convert_nontype_argument should do that.
> > >
> > > Indeed we do, the commit message was just rather sloppy/inaccurate...
> > > I'll try to correct it.
> > >
> > > >
> > > > > > This patch fixes this in a more general way at template
> > > > > > specialization
> > > > > > time by walking the template arguments of the specialization and
> > > > > > calling
> > > > > > mark_used on all entities used within. As before, the call to
> > > > > > mark_used
> > > > > > as it worst a no-op, but it compensates for the situation where we
> > > > > > end
> > > > > > up
> > > > > > forming a specialization from a template context in which mark_used
> > > > > > is
> > > > > > inhibited. Another approach would be to call mark_used whenever we
> > > > > > substitute a TEMPLATE_PARM_INDEX, but that would result in many more
> > > > > > redundant calls to mark_used compared to this approach.
> > > > > >
> > > > > > Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK
> > > > > > for
> > > > > > trunk?
> > > > > >
> > > > > > PR c++/53164
> > > > > > PR c++/105848
> > > > > >
> > > > > > gcc/cp/ChangeLog:
> > > > > >
> > > > > > * pt.cc (instantiate_class_template): Call
> > > > > > mark_template_arguments_used.
> > > > > > (tsubst_copy_and_build) <case CALL_EXPR>: Revert r13-995
> > > > > > change.
> > > > > > (mark_template_arguments_used): Define.
> > > > > > (instantiate_template): Call mark_template_arguments_used.
> > > > > >
> > > > > > gcc/testsuite/ChangeLog:
> > > > > >
> > > > > > * g++.dg/template/fn-ptr3a.C: New test.
> > > > > > * g++.dg/template/fn-ptr4.C: New test.
> > > > > > ---
> > > > > > gcc/cp/pt.cc | 51
> > > > > > ++++++++++++++++--------
> > > > > > gcc/testsuite/g++.dg/template/fn-ptr3a.C | 25 ++++++++++++
> > > > > > gcc/testsuite/g++.dg/template/fn-ptr4.C | 14 +++++++
> > > > > > 3 files changed, 74 insertions(+), 16 deletions(-)
> > > > > > create mode 100644 gcc/testsuite/g++.dg/template/fn-ptr3a.C
> > > > > > create mode 100644 gcc/testsuite/g++.dg/template/fn-ptr4.C
> > > > > >
> > > > > > diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
> > > > > > index 7e4a8de0c8b..9b3cc33331c 100644
> > > > > > --- a/gcc/cp/pt.cc
> > > > > > +++ b/gcc/cp/pt.cc
> > > > > > @@ -220,6 +220,7 @@ static tree make_argument_pack (tree);
> > > > > > static tree enclosing_instantiation_of (tree tctx);
> > > > > > static void instantiate_body (tree pattern, tree args, tree d,
> > > > > > bool
> > > > > > nested);
> > > > > > static tree maybe_dependent_member_ref (tree, tree,
> > > > > > tsubst_flags_t,
> > > > > > tree);
> > > > > > +static void mark_template_arguments_used (tree);
> > > > > > /* Make the current scope suitable for access checking when we
> > > > > > are
> > > > > > processing T. T can be FUNCTION_DECL for instantiated
> > > > > > function
> > > > > > @@ -12142,6 +12143,9 @@ instantiate_class_template (tree type)
> > > > > > cp_unevaluated_operand = 0;
> > > > > > c_inhibit_evaluation_warnings = 0;
> > > > > > }
> > > > > > +
> > > > > > + mark_template_arguments_used (INNERMOST_TEMPLATE_ARGS (args));
> > > > > > +
> > > > > > /* Use #pragma pack from the template context. */
> > > > > > saved_maximum_field_alignment = maximum_field_alignment;
> > > > > > maximum_field_alignment = TYPE_PRECISION (pattern);
> > > > > > @@ -21173,22 +21177,10 @@ tsubst_copy_and_build (tree t,
> > > > > > }
> > > > > > /* Remember that there was a reference to this entity.
> > > > > > */
> > > > > > - if (function != NULL_TREE)
> > > > > > - {
> > > > > > - tree inner = function;
> > > > > > - if (TREE_CODE (inner) == ADDR_EXPR
> > > > > > - && TREE_CODE (TREE_OPERAND (inner, 0)) ==
> > > > > > FUNCTION_DECL)
> > > > > > - /* We should already have called mark_used when taking
> > > > > > the
> > > > > > - address of this function, but do so again anyway to
> > > > > > make
> > > > > > - sure it's odr-used: at worst this is a no-op, but if
> > > > > > we
> > > > > > - obtained this FUNCTION_DECL as part of ahead-of-time
> > > > > > overload
> > > > > > - resolution then that call to mark_used wouldn't have
> > > > > > marked
> > > > > > it
> > > > > > - odr-used yet (53164). */
> > > > > > - inner = TREE_OPERAND (inner, 0);
> > > > > > - if (DECL_P (inner)
> > > > > > - && !mark_used (inner, complain) && !(complain &
> > > > > > tf_error))
> > > > > > - RETURN (error_mark_node);
> > > > > > - }
> > > > > > + if (function != NULL_TREE
> > > > > > + && DECL_P (function)
> > > > > > + && !mark_used (function, complain) && !(complain &
> > > > > > tf_error))
> > > > > > + RETURN (error_mark_node);
> > > > > > if (!maybe_fold_fn_template_args (function, complain))
> > > > > > return error_mark_node;
> > > > > > @@ -21883,6 +21875,31 @@ check_instantiated_args (tree tmpl, tree
> > > > > > args,
> > > > > > tsubst_flags_t complain)
> > > > > > return result;
> > > > > > }
> > > > > > +/* Call mark_used on each entity within the template arguments
> > > > > > ARGS of
> > > > > > some
> > > > > > + template specialization, to ensure that each such entity is
> > > > > > considered
> > > > > > + odr-used regardless of whether the specialization was first
> > > > > > formed
> > > > > > in
> > > > > > a
> > > > > > + template context.
> > > > > > +
> > > > > > + This function assumes push_to_top_level has been called
> > > > > > beforehand,
> > > > > > and
> > > > > > + that processing_template_decl has been set iff the template
> > > > > > arguments
> > > > > > + are dependent. */
> > > > > > +
> > > > > > +static void
> > > > > > +mark_template_arguments_used (tree args)
> > > > > > +{
> > > > > > + gcc_checking_assert (TMPL_ARGS_DEPTH (args) == 1);
> > > > > > +
> > > > > > + if (processing_template_decl)
> > > > > > + return;
> > > > > > +
> > > > > > + auto mark_used_r = [](tree *tp, int *, void *) {
> > > > > > + if (DECL_P (*tp))
> > > > > > + mark_used (*tp, tf_none);
> > > > > > + return NULL_TREE;
> > > > > > + };
> > > > > > + cp_walk_tree_without_duplicates (&args, mark_used_r, nullptr);
> > > > >
> > > > > Here's v2 which optimizes this function by not walking if
> > > > > !PRIMARY_TEMPLATE_P (since in that case the innermost arguments have
> > > > > already been walked when instantiating the context), and walking only
> > > > > non-type arguments:
> > > > >
> > > > > -- >8
> > > > >
> > > > > Subject: [PATCH] c++: improve "NTTP argument considered unused" fix
> > > > > [PR53164,
> > > > > PR105848]
> > > > >
> > > > > PR c++/53164
> > > > > PR c++/105848
> > > > >
> > > > > gcc/cp/ChangeLog:
> > > > >
> > > > > * pt.cc (instantiate_class_template): Call
> > > > > mark_template_arguments_used.
> > > > > (tsubst_copy_and_build) <case CALL_EXPR>: Revert r13-995 change.
> > > > > (mark_template_arguments_used): Define.
> > > > > (instantiate_template): Call mark_template_arguments_used.
> > > > >
> > > > > gcc/testsuite/ChangeLog:
> > > > >
> > > > > * g++.dg/template/fn-ptr3a.C: New test.
> > > > > * g++.dg/template/fn-ptr4.C: New test.
> > > > > ---
> > > > > gcc/cp/pt.cc | 57
> > > > > +++++++++++++++++-------
> > > > > gcc/testsuite/g++.dg/template/fn-ptr3a.C | 25 +++++++++++
> > > > > gcc/testsuite/g++.dg/template/fn-ptr4.C | 14 ++++++
> > > > > 3 files changed, 80 insertions(+), 16 deletions(-)
> > > > > create mode 100644 gcc/testsuite/g++.dg/template/fn-ptr3a.C
> > > > > create mode 100644 gcc/testsuite/g++.dg/template/fn-ptr4.C
> > > > >
> > > > > diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
> > > > > index 3bb98ebeac1..a87366bb616 100644
> > > > > --- a/gcc/cp/pt.cc
> > > > > +++ b/gcc/cp/pt.cc
> > > > > @@ -220,6 +220,7 @@ static tree make_argument_pack (tree);
> > > > > static tree enclosing_instantiation_of (tree tctx);
> > > > > static void instantiate_body (tree pattern, tree args, tree d, bool
> > > > > nested);
> > > > > static tree maybe_dependent_member_ref (tree, tree, tsubst_flags_t,
> > > > > tree);
> > > > > +static void mark_template_arguments_used (tree, tree);
> > > > > /* Make the current scope suitable for access checking when we
> > > > > are
> > > > > processing T. T can be FUNCTION_DECL for instantiated function
> > > > > @@ -12152,6 +12153,9 @@ instantiate_class_template (tree type)
> > > > > cp_unevaluated_operand = 0;
> > > > > c_inhibit_evaluation_warnings = 0;
> > > > > }
> > > > > +
> > > > > + mark_template_arguments_used (templ, CLASSTYPE_TI_ARGS (type));
> > > > > +
> > > > > /* Use #pragma pack from the template context. */
> > > > > saved_maximum_field_alignment = maximum_field_alignment;
> > > > > maximum_field_alignment = TYPE_PRECISION (pattern);
> > > > > @@ -21192,22 +21196,10 @@ tsubst_copy_and_build (tree t,
> > > > > }
> > > > > /* Remember that there was a reference to this entity. */
> > > > > - if (function != NULL_TREE)
> > > > > - {
> > > > > - tree inner = function;
> > > > > - if (TREE_CODE (inner) == ADDR_EXPR
> > > > > - && TREE_CODE (TREE_OPERAND (inner, 0)) == FUNCTION_DECL)
> > > > > - /* We should already have called mark_used when taking the
> > > > > - address of this function, but do so again anyway to
> > > > > make
> > > > > - sure it's odr-used: at worst this is a no-op, but if we
> > > > > - obtained this FUNCTION_DECL as part of ahead-of-time
> > > > > overload
> > > > > - resolution then that call to mark_used wouldn't have
> > > > > marked
> > > > > it
> > > > > - odr-used yet (53164). */
> > > > > - inner = TREE_OPERAND (inner, 0);
> > > > > - if (DECL_P (inner)
> > > > > - && !mark_used (inner, complain) && !(complain &
> > > > > tf_error))
> > > > > - RETURN (error_mark_node);
> > > > > - }
> > > > > + if (function != NULL_TREE
> > > > > + && DECL_P (function)
> > > > > + && !mark_used (function, complain) && !(complain &
> > > > > tf_error))
> > > > > + RETURN (error_mark_node);
> > > > > if (!maybe_fold_fn_template_args (function, complain))
> > > > > return error_mark_node;
> > > > > @@ -21902,6 +21894,37 @@ check_instantiated_args (tree tmpl, tree
> > > > > args,
> > > > > tsubst_flags_t complain)
> > > > > return result;
> > > > > }
> > > > > +/* Call mark_used on each entity within the non-type template
> > > > > arguments
> > > > > in
> > > > > + ARGS for a specialization of TMPL, to ensure that each such entity
> > > > > is
> > > > > + considered odr-used regardless of whether the specialization was
> > > > > first
> > > > > + formed in a template context.
> > > > > +
> > > > > + This function assumes push_to_top_level has been called
> > > > > beforehand,
> > > > > and
> > > > > + that processing_template_decl is set iff the template arguments
> > > > > are
> > > > > + dependent. */
> > > > > +
> > > > > +static void
> > > > > +mark_template_arguments_used (tree tmpl, tree args)
> > > > > +{
> > > > > + /* It suffices to do this only when fully specializing a primary
> > > > > template. */
> > > > > + if (processing_template_decl || !PRIMARY_TEMPLATE_P (tmpl))
> > > > > + return;
> > > > > +
> > > > > + /* We already marked outer arguments when specializing the context.
> > > > > */
> > > > > + args = INNERMOST_TEMPLATE_ARGS (args);
> > > > > +
> > > > > + for (tree arg : tree_vec_range (args))
> > > > > + if (!TYPE_P (arg))
> > > > > + {
> > > > > + auto mark_used_r = [](tree *tp, int *, void *) {
> > > > > + if (DECL_P (*tp))
> > > > > + mark_used (*tp, tf_none);
> > > > > + return NULL_TREE;
> > > > > + };
> > > > > + cp_walk_tree_without_duplicates (&args, mark_used_r, nullptr);
> > > >
> > > > Do we really need to walk into the args?
> > >
> > > Hmm, I think we might need to some sort for walking for class NTTP
> > > arguments since they could be nested CONSTRUCTORs. But for non-class
> > > arguments we know that an entity will only appear as a pointer- or
> > > reference-to-function/variable, so we could pattern match for such a
> > > structure directly. And doing so should be preferable because
> > > cp_walk_tree is relatively expensive and this is a relatively hot code
> > > path. So maybe the following would be preferable?
> > >
> > > -- >8 --
> > >
> > > Subject: [PATCH] c++: improve "NTTP argument considered unused" fix
> > > [PR53164,
> > > PR105848]
> > >
> > > r13-995-g733a792a2b2e16 worked around the problem of (pointer to)
> > > function NTTP arguments not always getting marked as odr-used by
> > > redundantly calling mark_used on the substituted ADDR_EXPR callee of a
> > > CALL_EXPR. That is just a narrow workaround however, since it assumes
> > > the function is later called. But the use as a template argument alone
> > > should constitute an odr-use of the function (since template arguments
> > > are an evaluated context, and we need its address); we shouldn't need to
> > > subsequently call or otherwise use the NTTP argument.
> > >
> > > This patch fixes this in a more general way at template specialization
> > > time by walking the template arguments of the specialization and calling
> > > mark_used on all entities used within. As before, the call to mark_used
> > > as it worst a no-op, but it compensates for the situation where we end
> > > up forming a specialization in a template context in which mark_used is
> > > inhibited.
> > >
> > > Another approach would be to call mark_used whenever we substitute a
> > > TEMPLATE_PARM_INDEX, but that would result in many more redundant calls
> > > to mark_used compared to this approach. And as the second testcase
> > > below illustrates, we also need to walk C++20 class NTTP arguments which
> > > can in theory be large and thus expensive to walk repeatedly. The
> > > change to invalid_tparm_referent_p is needed to avoid bogusly rejecting
> > > the testcase's class NTTP arguments containing function pointers.
> > >
> > > (The third testcase is unrelated to this fix, but it helped rule out an
> > > earlier approach I was considering and it seems we don't have existing
> > > test coverage for this situation.)
> > >
> > > PR c++/53164
> > > PR c++/105848
> > >
> > > gcc/cp/ChangeLog:
> > >
> > > * pt.cc (invalid_tparm_referent_p): Accept ADDR_EXPR of
> > > FUNCTION_DECL.
> > > (instantiate_class_template): Call mark_template_arguments_used.
> > > (tsubst_copy_and_build) <case CALL_EXPR>: Revert r13-995 change.
> > > (mark_template_arguments_used): Define.
> > > (instantiate_template): Call mark_template_arguments_used.
> > >
> > > gcc/testsuite/ChangeLog:
> > >
> > > * g++.dg/template/fn-ptr3a.C: New test.
> > > * g++.dg/template/fn-ptr3b.C: New test.
> > > * g++.dg/template/fn-ptr4.C: New test.
> > > ---
> > > gcc/cp/pt.cc | 78 ++++++++++++++++++------
> > > gcc/testsuite/g++.dg/template/fn-ptr3a.C | 25 ++++++++
> > > gcc/testsuite/g++.dg/template/fn-ptr3b.C | 28 +++++++++
> > > gcc/testsuite/g++.dg/template/fn-ptr4.C | 14 +++++
> > > 4 files changed, 127 insertions(+), 18 deletions(-)
> > > create mode 100644 gcc/testsuite/g++.dg/template/fn-ptr3a.C
> > > create mode 100644 gcc/testsuite/g++.dg/template/fn-ptr3b.C
> > > create mode 100644 gcc/testsuite/g++.dg/template/fn-ptr4.C
> > >
> > > diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
> > > index e514a277872..01ab220320c 100644
> > > --- a/gcc/cp/pt.cc
> > > +++ b/gcc/cp/pt.cc
> > > @@ -220,6 +220,7 @@ static tree make_argument_pack (tree);
> > > static tree enclosing_instantiation_of (tree tctx);
> > > static void instantiate_body (tree pattern, tree args, tree d, bool
> > > nested);
> > > static tree maybe_dependent_member_ref (tree, tree, tsubst_flags_t,
> > > tree);
> > > +static void mark_template_arguments_used (tree, tree);
> > > /* Make the current scope suitable for access checking when we are
> > > processing T. T can be FUNCTION_DECL for instantiated function
> > > @@ -7142,12 +7143,13 @@ invalid_tparm_referent_p (tree type, tree expr,
> > > tsubst_flags_t complain)
> > > decl = TREE_OPERAND (decl, 0);
> > > }
> > > - if (!VAR_P (decl))
> > > + if (!VAR_OR_FUNCTION_DECL_P (decl))
> > > {
> > > if (complain & tf_error)
> > > error_at (cp_expr_loc_or_input_loc (expr),
> > > "%qE is not a valid template argument of type
> > > %qT "
> > > - "because %qE is not a variable", expr, type, decl);
> > > + "because %qE is not a variable or function",
> > > + expr, type, decl);
> > > return true;
> > > }
> > > else if (cxx_dialect < cxx11 && !DECL_EXTERNAL_LINKAGE_P (decl))
> > > @@ -12152,6 +12154,9 @@ instantiate_class_template (tree type)
> > > cp_unevaluated_operand = 0;
> > > c_inhibit_evaluation_warnings = 0;
> > > }
> > > +
> > > + mark_template_arguments_used (templ, CLASSTYPE_TI_ARGS (type));
> > > +
> > > /* Use #pragma pack from the template context. */
> > > saved_maximum_field_alignment = maximum_field_alignment;
> > > maximum_field_alignment = TYPE_PRECISION (pattern);
> > > @@ -21192,22 +21197,10 @@ tsubst_copy_and_build (tree t,
> > > }
> > > /* Remember that there was a reference to this entity. */
> > > - if (function != NULL_TREE)
> > > - {
> > > - tree inner = function;
> > > - if (TREE_CODE (inner) == ADDR_EXPR
> > > - && TREE_CODE (TREE_OPERAND (inner, 0)) == FUNCTION_DECL)
> > > - /* We should already have called mark_used when taking the
> > > - address of this function, but do so again anyway to make
> > > - sure it's odr-used: at worst this is a no-op, but if we
> > > - obtained this FUNCTION_DECL as part of ahead-of-time overload
> > > - resolution then that call to mark_used wouldn't have marked
> > > it
> > > - odr-used yet (53164). */
> > > - inner = TREE_OPERAND (inner, 0);
> > > - if (DECL_P (inner)
> > > - && !mark_used (inner, complain) && !(complain & tf_error))
> > > - RETURN (error_mark_node);
> > > - }
> > > + if (function != NULL_TREE
> > > + && DECL_P (function)
> > > + && !mark_used (function, complain) && !(complain & tf_error))
> > > + RETURN (error_mark_node);
> > > if (!maybe_fold_fn_template_args (function, complain))
> > > return error_mark_node;
> > > @@ -21902,6 +21895,53 @@ check_instantiated_args (tree tmpl, tree args,
> > > tsubst_flags_t complain)
> > > return result;
> > > }
> > > +/* Call mark_used on each entity within the non-type template arguments
> > > in
> > > + ARGS for a specialization of TMPL, to ensure that each such entity is
> > > + considered odr-used regardless of whether the specialization was first
> > > + formed in a template context.
> > > +
> > > + This function assumes push_to_top_level has been called beforehand,
> > > and
> > > + that processing_template_decl is set iff the template arguments are
> > > + dependent. */
> > > +
> > > +static void
> > > +mark_template_arguments_used (tree tmpl, tree args)
> > > +{
> > > + /* It suffices to do this only when fully specializing a primary
> > > template. */
> > > + if (processing_template_decl || !PRIMARY_TEMPLATE_P (tmpl))
> > > + return;
> > > +
> > > + /* We already marked outer arguments when specializing the context. */
> > > + args = INNERMOST_TEMPLATE_ARGS (args);
> > > +
> > > + for (tree arg : tree_vec_range (args))
> > > + {
> > > + /* A (pointer/reference to) function or variable NTTP argument. */
> > > + if (TREE_CODE (arg) == ADDR_EXPR
> > > + || TREE_CODE (arg) == INDIRECT_REF)
> > > + {
> > > + while (TREE_CODE (arg) == ADDR_EXPR
> > > + || REFERENCE_REF_P (arg)
> > > + || CONVERT_EXPR_P (arg))
> > > + arg = TREE_OPERAND (arg, 0);
> > > + if (DECL_P (arg))
> > > + mark_used (arg, tf_none);
> >
> > Passing tf_none and also ignoring the return value needs a comment
> > justifying
> > why you assume it can't fail.
>
> *nod* Since these calls to mark_used ought to be at worst redundant, it
> should be safe to even assert
>
> bool ok = mark_used (arg, tf_none);
> gcc_checking_assert (ok || seen_error ());
>
> >
> > > + }
> > > + /* A class NTTP argument. */
> > > + else if (VAR_P (arg)
> > > + && DECL_NTTP_OBJECT_P (arg))
> >
> > Maybe avoid doing this multiple times for the same NTTP object by gating it
> > on
> > DECL_ODR_USED (arg)?
>
> Looks like these VAR_DECLs don't have DECL_LANG_SPECIFIC, so we can't
> inspect DECL_ODR_USED for them..
>
> It occurred to me that instantiate_class_template is perhaps the wrong
> place to do this marking; it'd be more appropriate to do it in
> lookup_template_class when forming the type specialization rather than
> when instantiating its definition. So in order to handle all template
> kinds consistently, I think we should do the marking in either
> instantiate_class_template and instantiate_body (i.e. at instantiation
> time), or in lookup_template_class and instantiate_template (i.e. at
> specialization time), but currently the patch does it in
> instantiate_class_template and instantiate_template which sounds
> consistent but it's sadly not.
>
> However, lookup_template_class doesn't seem to call push_to_top_level at
> all, so if we want to call mark_used uninhibited on the template
> arguments from there I think we need to add a flag to mark_used that
> simply disables its
>
> if (processing_template_decl || in_template_function ())
> return true;
>
> early exit. IIUC the purpose of this early exit is to avoid
> instantiating a template due to a use from an uninstantiated template,
> under the assumption that we'll call mark_used again at instantiation
> time for that use, but in this case it seems we need to allow such
> ahead-of-time instantiation since we don't reprocess the template
> arguments of a non-dependent specialization again at instantiation time.
>
> This is quite the can of worms :/
This is what I have so far, it's imperfect but perhaps good enough?
bootstrapped and regtested on x86_64-pc-linux-gnu:
-- >8 --
Subject: [PATCH] c++: improve "NTTP argument considered unused" fix [PR53164,
PR105848]
PR c++/53164
PR c++/105848
gcc/cp/ChangeLog:
* pt.cc (invalid_tparm_referent_p): Accept ADDR_EXPR of
FUNCTION_DECL.
(instantiate_class_template): Call mark_template_arguments_used.
(tsubst_copy_and_build) <case CALL_EXPR>: Revert r13-995 change.
(mark_template_arguments_used): Define.
(instantiate_template): Call mark_template_arguments_used.
gcc/testsuite/ChangeLog:
* g++.dg/template/fn-ptr3a.C: New test.
* g++.dg/template/fn-ptr3b.C: New test.
* g++.dg/template/fn-ptr4.C: New test.
---
gcc/cp/pt.cc | 88 +++++++++++++++++++-----
gcc/testsuite/g++.dg/template/fn-ptr3a.C | 25 +++++++
gcc/testsuite/g++.dg/template/fn-ptr3b.C | 28 ++++++++
gcc/testsuite/g++.dg/template/fn-ptr4.C | 14 ++++
4 files changed, 137 insertions(+), 18 deletions(-)
create mode 100644 gcc/testsuite/g++.dg/template/fn-ptr3a.C
create mode 100644 gcc/testsuite/g++.dg/template/fn-ptr3b.C
create mode 100644 gcc/testsuite/g++.dg/template/fn-ptr4.C
diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index dd7f0db9658..83902b0be8d 100644
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -220,6 +220,7 @@ static tree make_argument_pack (tree);
static tree enclosing_instantiation_of (tree tctx);
static void instantiate_body (tree pattern, tree args, tree d, bool nested);
static tree maybe_dependent_member_ref (tree, tree, tsubst_flags_t, tree);
+static void mark_template_arguments_used (tree, tree);
/* Make the current scope suitable for access checking when we are
processing T. T can be FUNCTION_DECL for instantiated function
@@ -7142,12 +7143,13 @@ invalid_tparm_referent_p (tree type, tree expr,
tsubst_flags_t complain)
decl = TREE_OPERAND (decl, 0);
}
- if (!VAR_P (decl))
+ if (!VAR_OR_FUNCTION_DECL_P (decl))
{
if (complain & tf_error)
error_at (cp_expr_loc_or_input_loc (expr),
"%qE is not a valid template argument of type %qT "
- "because %qE is not a variable", expr, type, decl);
+ "because %qE is not a variable or function",
+ expr, type, decl);
return true;
}
else if (cxx_dialect < cxx11 && !DECL_EXTERNAL_LINKAGE_P (decl))
@@ -12152,6 +12154,9 @@ instantiate_class_template (tree type)
cp_unevaluated_operand = 0;
c_inhibit_evaluation_warnings = 0;
}
+
+ mark_template_arguments_used (templ, CLASSTYPE_TI_ARGS (type));
+
/* Use #pragma pack from the template context. */
saved_maximum_field_alignment = maximum_field_alignment;
maximum_field_alignment = TYPE_PRECISION (pattern);
@@ -21192,22 +21197,10 @@ tsubst_copy_and_build (tree t,
}
/* Remember that there was a reference to this entity. */
- if (function != NULL_TREE)
- {
- tree inner = function;
- if (TREE_CODE (inner) == ADDR_EXPR
- && TREE_CODE (TREE_OPERAND (inner, 0)) == FUNCTION_DECL)
- /* We should already have called mark_used when taking the
- address of this function, but do so again anyway to make
- sure it's odr-used: at worst this is a no-op, but if we
- obtained this FUNCTION_DECL as part of ahead-of-time overload
- resolution then that call to mark_used wouldn't have marked it
- odr-used yet (53164). */
- inner = TREE_OPERAND (inner, 0);
- if (DECL_P (inner)
- && !mark_used (inner, complain) && !(complain & tf_error))
- RETURN (error_mark_node);
- }
+ if (function != NULL_TREE
+ && DECL_P (function)
+ && !mark_used (function, complain) && !(complain & tf_error))
+ RETURN (error_mark_node);
if (!maybe_fold_fn_template_args (function, complain))
return error_mark_node;
@@ -21902,6 +21895,63 @@ check_instantiated_args (tree tmpl, tree args,
tsubst_flags_t complain)
return result;
}
+/* Call mark_used on each entity within the non-type template arguments in
+ ARGS for a specialization of TMPL, to ensure that each such entity is
+ considered odr-used (and therefore marked for instantiation) regardless of
+ whether the specialization was first formed in a template context (which
+ inhibits mark_used).
+
+ This function assumes push_to_top_level has been called beforehand, and
+ that processing_template_decl is set iff the template arguments are
+ dependent. */
+
+static void
+mark_template_arguments_used (tree tmpl, tree args)
+{
+ /* It suffices to do this only when fully specializing a primary template.
*/
+ if (processing_template_decl || !PRIMARY_TEMPLATE_P (tmpl))
+ return;
+
+ /* We already marked outer arguments when specializing the context. */
+ args = INNERMOST_TEMPLATE_ARGS (args);
+
+ for (tree arg : tree_vec_range (args))
+ {
+ /* A (pointer/reference to) function or variable NTTP argument. */
+ if (TREE_CODE (arg) == ADDR_EXPR
+ || TREE_CODE (arg) == INDIRECT_REF)
+ {
+ while (TREE_CODE (arg) == ADDR_EXPR
+ || REFERENCE_REF_P (arg)
+ || CONVERT_EXPR_P (arg))
+ arg = TREE_OPERAND (arg, 0);
+ if (VAR_OR_FUNCTION_DECL_P (arg))
+ {
+ /* Pass tf_none to avoid duplicate diagnostics: the call
+ ought to succeed without error, or a previous call
+ must have already issued an error. */
+ bool ok = mark_used (arg, tf_none);
+ gcc_checking_assert (ok || seen_error ());
+ }
+ }
+ /* A class NTTP argument. */
+ else if (VAR_P (arg)
+ && DECL_NTTP_OBJECT_P (arg))
+ {
+ auto mark_used_r = [](tree *tp, int *, void *) {
+ if (VAR_OR_FUNCTION_DECL_P (*tp))
+ {
+ bool ok = mark_used (*tp, tf_none);
+ gcc_checking_assert (ok || seen_error ());
+ }
+ return NULL_TREE;
+ };
+ cp_walk_tree_without_duplicates (&DECL_INITIAL (arg),
+ mark_used_r, nullptr);
+ }
+ }
+}
+
/* We're out of SFINAE context now, so generate diagnostics for the access
errors we saw earlier when instantiating D from TMPL and ARGS. */
@@ -22031,6 +22081,8 @@ instantiate_template (tree tmpl, tree orig_args,
tsubst_flags_t complain)
push_nested_class (ctx);
}
+ mark_template_arguments_used (gen_tmpl, targ_ptr);
+
tree pattern = DECL_TEMPLATE_RESULT (gen_tmpl);
fndecl = NULL_TREE;
diff --git a/gcc/testsuite/g++.dg/template/fn-ptr3a.C
b/gcc/testsuite/g++.dg/template/fn-ptr3a.C
new file mode 100644
index 00000000000..7456be5d51f
--- /dev/null
+++ b/gcc/testsuite/g++.dg/template/fn-ptr3a.C
@@ -0,0 +1,25 @@
+// PR c++/53164
+// PR c++/105848
+// A stricter version of fn-ptr3.C that verifies using f as a template
+// argument alone constitutes an odr-use.
+
+template<class T>
+void f(T) { T::fail; } // { dg-error "fail" }
+
+template<void (*P)(int)>
+struct A {
+ static void wrap();
+};
+
+template<void (&P)(char)>
+void wrap();
+
+template<int>
+void g() {
+ A<f>::wrap(); // { dg-message "required from here" }
+ wrap<f>(); // { dg-message "required from here" }
+}
+
+int main() {
+ g<0>();
+}
diff --git a/gcc/testsuite/g++.dg/template/fn-ptr3b.C
b/gcc/testsuite/g++.dg/template/fn-ptr3b.C
new file mode 100644
index 00000000000..90d988ce896
--- /dev/null
+++ b/gcc/testsuite/g++.dg/template/fn-ptr3b.C
@@ -0,0 +1,28 @@
+// PR c++/53164
+// PR c++/105848
+// A C++20 version of fn-ptr3a.C using class NTTPs.
+// { dg-do compile { target c++20 } }
+
+template<class T>
+void f(T) { T::fail; } // { dg-error "fail" }
+
+struct B_int { void (*P)(int); };
+struct B_char { void (*P)(char); };
+
+template<B_int B>
+struct A {
+ static void wrap();
+};
+
+template<B_char B>
+void wrap();
+
+template<int>
+void g() {
+ A<B_int{f}>::wrap(); // { dg-message "required from here" }
+ wrap<B_char{f}>(); // { dg-message "required from here" }
+}
+
+int main() {
+ g<0>();
+}
diff --git a/gcc/testsuite/g++.dg/template/fn-ptr4.C
b/gcc/testsuite/g++.dg/template/fn-ptr4.C
new file mode 100644
index 00000000000..36551ec5d7f
--- /dev/null
+++ b/gcc/testsuite/g++.dg/template/fn-ptr4.C
@@ -0,0 +1,14 @@
+// { dg-do compile }
+
+template<void (*P)()>
+void wrap() {
+ P(); // OK, despite A::g not being accessible from here.
+}
+
+struct A {
+ static void f() {
+ wrap<A::g>();
+ }
+private:
+ static void g();
+};
--
2.40.0.153.g6369acd968
