[RFA,(tree)] c++: lambda in template default argument [PR103186]

The problem with this testcase was that since my patch for PR97900 we
weren't preserving DECL_UID identity for parameters of instantiations of
templated functions, so using those parameters as the keys for the
defarg_inst map broke.  I think this was always fragile given the
possibility of redeclarations, so instead of reverting that change let's
switch to keying off the function.

Memory use compiling stdc++.h is not noticeably different.

Tested x86_64-pc-linux-gnu.  Is the tree.{h,cc} change, just moving the class
definition from one to the other, OK for trunk?

	PR c++/103186

gcc/ChangeLog:

	* tree.h (struct tree_vec_map_cache_hasher): Move from...
	* tree.cc (struct tree_vec_map_cache_hasher): ...here.

gcc/cp/ChangeLog:

	* pt.cc (defarg_inst): Use tree_vec_map_cache_hasher.
	(defarg_inst_for): New.
	(tsubst_default_argument): Adjust.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp0x/lambda/lambda-defarg10.C: New test.
---
 gcc/tree.h                                    | 17 ++++++++
 gcc/cp/pt.cc                                  | 43 +++++++++++++++----
 .../g++.dg/cpp0x/lambda/lambda-defarg10.C     | 21 +++++++++
 gcc/tree.cc                                   | 17 --------
 4 files changed, 72 insertions(+), 26 deletions(-)
 create mode 100644 gcc/testsuite/g++.dg/cpp0x/lambda/lambda-defarg10.C


base-commit: 9bf217920457f2e2d46b601f24721780a20a031b
prerequisite-patch-id: c7ab4056fcbd782232c8dc091597602ecd4a7a48

Ping.

On 1/26/22 18:16, Jason Merrill wrote:
> The problem with this testcase was that since my patch for PR97900 we
> weren't preserving DECL_UID identity for parameters of instantiations of
> templated functions, so using those parameters as the keys for the
> defarg_inst map broke.  I think this was always fragile given the
> possibility of redeclarations, so instead of reverting that change let's
> switch to keying off the function.
> 
> Memory use compiling stdc++.h is not noticeably different.
> 
> Tested x86_64-pc-linux-gnu.  Is the tree.{h,cc} change, just moving the class
> definition from one to the other, OK for trunk?
> 
> 	PR c++/103186
> 
> gcc/ChangeLog:
> 
> 	* tree.h (struct tree_vec_map_cache_hasher): Move from...
> 	* tree.cc (struct tree_vec_map_cache_hasher): ...here.
> 
> gcc/cp/ChangeLog:
> 
> 	* pt.cc (defarg_inst): Use tree_vec_map_cache_hasher.
> 	(defarg_inst_for): New.
> 	(tsubst_default_argument): Adjust.
> 
> gcc/testsuite/ChangeLog:
> 
> 	* g++.dg/cpp0x/lambda/lambda-defarg10.C: New test.
> ---
>   gcc/tree.h                                    | 17 ++++++++
>   gcc/cp/pt.cc                                  | 43 +++++++++++++++----
>   .../g++.dg/cpp0x/lambda/lambda-defarg10.C     | 21 +++++++++
>   gcc/tree.cc                                   | 17 --------
>   4 files changed, 72 insertions(+), 26 deletions(-)
>   create mode 100644 gcc/testsuite/g++.dg/cpp0x/lambda/lambda-defarg10.C
> 
> diff --git a/gcc/tree.h b/gcc/tree.h
> index 30bc53c2996..c5617fbcc61 100644
> --- a/gcc/tree.h
> +++ b/gcc/tree.h
> @@ -5559,6 +5559,23 @@ struct tree_decl_map_cache_hasher : ggc_cache_ptr_hash<tree_decl_map>
>   #define tree_vec_map_hash tree_decl_map_hash
>   #define tree_vec_map_marked_p tree_map_base_marked_p
>   
> +struct tree_vec_map_cache_hasher : ggc_cache_ptr_hash<tree_vec_map>
> +{
> +  static hashval_t hash (tree_vec_map *m) { return DECL_UID (m->base.from); }
> +
> +  static bool
> +  equal (tree_vec_map *a, tree_vec_map *b)
> +  {
> +    return a->base.from == b->base.from;
> +  }
> +
> +  static int
> +  keep_cache_entry (tree_vec_map *&m)
> +  {
> +    return ggc_marked_p (m->base.from);
> +  }
> +};
> +
>   /* Hasher for tree decls.  Pointer equality is enough here, but the DECL_UID
>      is a better hash than the pointer value and gives a predictable traversal
>      order.  Additionally it can be used across PCH save/restore.  */
> diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
> index 6fbda676527..db99b988fc3 100644
> --- a/gcc/cp/pt.cc
> +++ b/gcc/cp/pt.cc
> @@ -13666,7 +13666,36 @@ tsubst_aggr_type (tree t,
>       }
>   }
>   
> -static GTY((cache)) decl_tree_cache_map *defarg_inst;
> +/* Map from a FUNCTION_DECL to a vec of default argument instantiations.  */
> +
> +static GTY((cache)) hash_table<tree_vec_map_cache_hasher> *defarg_inst;
> +
> +/* Return a reference to the slot for the defarg inst of PARM.  */
> +
> +tree &
> +defarg_inst_for (tree parm)
> +{
> +  if (!defarg_inst)
> +    defarg_inst = hash_table<tree_vec_map_cache_hasher>::create_ggc (13);
> +  tree fn = DECL_CONTEXT (parm);
> +  tree_vec_map in = { fn, nullptr };
> +  tree_vec_map **slot
> +    = defarg_inst->find_slot_with_hash (&in, DECL_UID (fn), INSERT);
> +  if (!*slot)
> +    {
> +      *slot = ggc_alloc<tree_vec_map> ();
> +      **slot = in;
> +    }
> +
> +  /* Index in reverse order to avoid allocating space for initial parameters
> +     that don't have default arguments.  */
> +  unsigned ridx = list_length (parm);
> +
> +  vec<tree,va_gc> *&defs = (*slot)->to;
> +  if (vec_safe_length (defs) < ridx)
> +    vec_safe_grow_cleared (defs, ridx);
> +  return (*defs)[ridx - 1];
> +}
>   
>   /* Substitute into the default argument ARG (a default argument for
>      FN), which has the indicated TYPE.  */
> @@ -13696,9 +13725,9 @@ tsubst_default_argument (tree fn, int parmnum, tree type, tree arg,
>   
>     gcc_assert (same_type_ignoring_top_level_qualifiers_p (type, parmtype));
>   
> -  tree *slot;
> -  if (defarg_inst && (slot = defarg_inst->get (parm)))
> -    return *slot;
> +  tree &inst = defarg_inst_for (parm);
> +  if (inst)
> +    return inst;
>   
>     /* This default argument came from a template.  Instantiate the
>        default argument here, not in tsubst.  In the case of
> @@ -13743,11 +13772,7 @@ tsubst_default_argument (tree fn, int parmnum, tree type, tree arg,
>     pop_from_top_level ();
>   
>     if (arg != error_mark_node && !cp_unevaluated_operand)
> -    {
> -      if (!defarg_inst)
> -	defarg_inst = decl_tree_cache_map::create_ggc (37);
> -      defarg_inst->put (parm, arg);
> -    }
> +    inst = arg;
>   
>     return arg;
>   }
> diff --git a/gcc/testsuite/g++.dg/cpp0x/lambda/lambda-defarg10.C b/gcc/testsuite/g++.dg/cpp0x/lambda/lambda-defarg10.C
> new file mode 100644
> index 00000000000..e08eb4f5e56
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/cpp0x/lambda/lambda-defarg10.C
> @@ -0,0 +1,21 @@
> +// PR c++/103186
> +// { dg-do compile { target c++11 } }
> +
> +struct f
> +{
> +  template<class T1>
> +   f(const T1&){}
> +};
> +
> +
> +template<typename T> class A {
> +public:
> +    void foo(A<T> a, const f& fn = [](){}) { }
> +    void bar(A<T> a) { foo(a); }
> +};
> +int main() {
> +    A<int> a;
> +    a.foo(a);
> +    a.bar(a);
> +    return 0;
> +}
> diff --git a/gcc/tree.cc b/gcc/tree.cc
> index c4b36619e6a..6bd3b14c93c 100644
> --- a/gcc/tree.cc
> +++ b/gcc/tree.cc
> @@ -242,23 +242,6 @@ static GTY ((cache))
>   static GTY ((cache))
>        hash_table<tree_decl_map_cache_hasher> *value_expr_for_decl;
>   
> -struct tree_vec_map_cache_hasher : ggc_cache_ptr_hash<tree_vec_map>
> -{
> -  static hashval_t hash (tree_vec_map *m) { return DECL_UID (m->base.from); }
> -
> -  static bool
> -  equal (tree_vec_map *a, tree_vec_map *b)
> -  {
> -    return a->base.from == b->base.from;
> -  }
> -
> -  static int
> -  keep_cache_entry (tree_vec_map *&m)
> -  {
> -    return ggc_marked_p (m->base.from);
> -  }
> -};
> -
>   static GTY ((cache))
>        hash_table<tree_vec_map_cache_hasher> *debug_args_for_decl;
>   
> 
> base-commit: 9bf217920457f2e2d46b601f24721780a20a031b
> prerequisite-patch-id: c7ab4056fcbd782232c8dc091597602ecd4a7a48

On Wed, Jan 26, 2022 at 06:16:34PM -0500, Jason Merrill via Gcc-patches wrote:
> The problem with this testcase was that since my patch for PR97900 we
> weren't preserving DECL_UID identity for parameters of instantiations of
> templated functions, so using those parameters as the keys for the
> defarg_inst map broke.  I think this was always fragile given the
> possibility of redeclarations, so instead of reverting that change let's
> switch to keying off the function.
> 
> Memory use compiling stdc++.h is not noticeably different.
> 
> Tested x86_64-pc-linux-gnu.  Is the tree.{h,cc} change, just moving the class
> definition from one to the other, OK for trunk?

Ok.

> 	PR c++/103186
> 
> gcc/ChangeLog:
> 
> 	* tree.h (struct tree_vec_map_cache_hasher): Move from...
> 	* tree.cc (struct tree_vec_map_cache_hasher): ...here.
> 
> gcc/cp/ChangeLog:
> 
> 	* pt.cc (defarg_inst): Use tree_vec_map_cache_hasher.
> 	(defarg_inst_for): New.
> 	(tsubst_default_argument): Adjust.
> 
> gcc/testsuite/ChangeLog:
> 
> 	* g++.dg/cpp0x/lambda/lambda-defarg10.C: New test.

	Jakub

On Mon, Jan 31, 2022 at 10:34 PM Jason Merrill via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
> Ping.

OK.

Richard.

> On 1/26/22 18:16, Jason Merrill wrote:
> > The problem with this testcase was that since my patch for PR97900 we
> > weren't preserving DECL_UID identity for parameters of instantiations of
> > templated functions, so using those parameters as the keys for the
> > defarg_inst map broke.  I think this was always fragile given the
> > possibility of redeclarations, so instead of reverting that change let's
> > switch to keying off the function.
> >
> > Memory use compiling stdc++.h is not noticeably different.
> >
> > Tested x86_64-pc-linux-gnu.  Is the tree.{h,cc} change, just moving the class
> > definition from one to the other, OK for trunk?
> >
> >       PR c++/103186
> >
> > gcc/ChangeLog:
> >
> >       * tree.h (struct tree_vec_map_cache_hasher): Move from...
> >       * tree.cc (struct tree_vec_map_cache_hasher): ...here.
> >
> > gcc/cp/ChangeLog:
> >
> >       * pt.cc (defarg_inst): Use tree_vec_map_cache_hasher.
> >       (defarg_inst_for): New.
> >       (tsubst_default_argument): Adjust.
> >
> > gcc/testsuite/ChangeLog:
> >
> >       * g++.dg/cpp0x/lambda/lambda-defarg10.C: New test.
> > ---
> >   gcc/tree.h                                    | 17 ++++++++
> >   gcc/cp/pt.cc                                  | 43 +++++++++++++++----
> >   .../g++.dg/cpp0x/lambda/lambda-defarg10.C     | 21 +++++++++
> >   gcc/tree.cc                                   | 17 --------
> >   4 files changed, 72 insertions(+), 26 deletions(-)
> >   create mode 100644 gcc/testsuite/g++.dg/cpp0x/lambda/lambda-defarg10.C
> >
> > diff --git a/gcc/tree.h b/gcc/tree.h
> > index 30bc53c2996..c5617fbcc61 100644
> > --- a/gcc/tree.h
> > +++ b/gcc/tree.h
> > @@ -5559,6 +5559,23 @@ struct tree_decl_map_cache_hasher : ggc_cache_ptr_hash<tree_decl_map>
> >   #define tree_vec_map_hash tree_decl_map_hash
> >   #define tree_vec_map_marked_p tree_map_base_marked_p
> >
> > +struct tree_vec_map_cache_hasher : ggc_cache_ptr_hash<tree_vec_map>
> > +{
> > +  static hashval_t hash (tree_vec_map *m) { return DECL_UID (m->base.from); }
> > +
> > +  static bool
> > +  equal (tree_vec_map *a, tree_vec_map *b)
> > +  {
> > +    return a->base.from == b->base.from;
> > +  }
> > +
> > +  static int
> > +  keep_cache_entry (tree_vec_map *&m)
> > +  {
> > +    return ggc_marked_p (m->base.from);
> > +  }
> > +};
> > +
> >   /* Hasher for tree decls.  Pointer equality is enough here, but the DECL_UID
> >      is a better hash than the pointer value and gives a predictable traversal
> >      order.  Additionally it can be used across PCH save/restore.  */
> > diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
> > index 6fbda676527..db99b988fc3 100644
> > --- a/gcc/cp/pt.cc
> > +++ b/gcc/cp/pt.cc
> > @@ -13666,7 +13666,36 @@ tsubst_aggr_type (tree t,
> >       }
> >   }
> >
> > -static GTY((cache)) decl_tree_cache_map *defarg_inst;
> > +/* Map from a FUNCTION_DECL to a vec of default argument instantiations.  */
> > +
> > +static GTY((cache)) hash_table<tree_vec_map_cache_hasher> *defarg_inst;
> > +
> > +/* Return a reference to the slot for the defarg inst of PARM.  */
> > +
> > +tree &
> > +defarg_inst_for (tree parm)
> > +{
> > +  if (!defarg_inst)
> > +    defarg_inst = hash_table<tree_vec_map_cache_hasher>::create_ggc (13);
> > +  tree fn = DECL_CONTEXT (parm);
> > +  tree_vec_map in = { fn, nullptr };
> > +  tree_vec_map **slot
> > +    = defarg_inst->find_slot_with_hash (&in, DECL_UID (fn), INSERT);
> > +  if (!*slot)
> > +    {
> > +      *slot = ggc_alloc<tree_vec_map> ();
> > +      **slot = in;
> > +    }
> > +
> > +  /* Index in reverse order to avoid allocating space for initial parameters
> > +     that don't have default arguments.  */
> > +  unsigned ridx = list_length (parm);
> > +
> > +  vec<tree,va_gc> *&defs = (*slot)->to;
> > +  if (vec_safe_length (defs) < ridx)
> > +    vec_safe_grow_cleared (defs, ridx);
> > +  return (*defs)[ridx - 1];
> > +}
> >
> >   /* Substitute into the default argument ARG (a default argument for
> >      FN), which has the indicated TYPE.  */
> > @@ -13696,9 +13725,9 @@ tsubst_default_argument (tree fn, int parmnum, tree type, tree arg,
> >
> >     gcc_assert (same_type_ignoring_top_level_qualifiers_p (type, parmtype));
> >
> > -  tree *slot;
> > -  if (defarg_inst && (slot = defarg_inst->get (parm)))
> > -    return *slot;
> > +  tree &inst = defarg_inst_for (parm);
> > +  if (inst)
> > +    return inst;
> >
> >     /* This default argument came from a template.  Instantiate the
> >        default argument here, not in tsubst.  In the case of
> > @@ -13743,11 +13772,7 @@ tsubst_default_argument (tree fn, int parmnum, tree type, tree arg,
> >     pop_from_top_level ();
> >
> >     if (arg != error_mark_node && !cp_unevaluated_operand)
> > -    {
> > -      if (!defarg_inst)
> > -     defarg_inst = decl_tree_cache_map::create_ggc (37);
> > -      defarg_inst->put (parm, arg);
> > -    }
> > +    inst = arg;
> >
> >     return arg;
> >   }
> > diff --git a/gcc/testsuite/g++.dg/cpp0x/lambda/lambda-defarg10.C b/gcc/testsuite/g++.dg/cpp0x/lambda/lambda-defarg10.C
> > new file mode 100644
> > index 00000000000..e08eb4f5e56
> > --- /dev/null
> > +++ b/gcc/testsuite/g++.dg/cpp0x/lambda/lambda-defarg10.C
> > @@ -0,0 +1,21 @@
> > +// PR c++/103186
> > +// { dg-do compile { target c++11 } }
> > +
> > +struct f
> > +{
> > +  template<class T1>
> > +   f(const T1&){}
> > +};
> > +
> > +
> > +template<typename T> class A {
> > +public:
> > +    void foo(A<T> a, const f& fn = [](){}) { }
> > +    void bar(A<T> a) { foo(a); }
> > +};
> > +int main() {
> > +    A<int> a;
> > +    a.foo(a);
> > +    a.bar(a);
> > +    return 0;
> > +}
> > diff --git a/gcc/tree.cc b/gcc/tree.cc
> > index c4b36619e6a..6bd3b14c93c 100644
> > --- a/gcc/tree.cc
> > +++ b/gcc/tree.cc
> > @@ -242,23 +242,6 @@ static GTY ((cache))
> >   static GTY ((cache))
> >        hash_table<tree_decl_map_cache_hasher> *value_expr_for_decl;
> >
> > -struct tree_vec_map_cache_hasher : ggc_cache_ptr_hash<tree_vec_map>
> > -{
> > -  static hashval_t hash (tree_vec_map *m) { return DECL_UID (m->base.from); }
> > -
> > -  static bool
> > -  equal (tree_vec_map *a, tree_vec_map *b)
> > -  {
> > -    return a->base.from == b->base.from;
> > -  }
> > -
> > -  static int
> > -  keep_cache_entry (tree_vec_map *&m)
> > -  {
> > -    return ggc_marked_p (m->base.from);
> > -  }
> > -};
> > -
> >   static GTY ((cache))
> >        hash_table<tree_vec_map_cache_hasher> *debug_args_for_decl;
> >
> >
> > base-commit: 9bf217920457f2e2d46b601f24721780a20a031b
> > prerequisite-patch-id: c7ab4056fcbd782232c8dc091597602ecd4a7a48
>