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

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