Make bp_location derive from refcounted_object

This changes bp_location to derive from refcounted_object, introduces
a ref_ptr specialization for this type, and then changes
bpstats::bp_location_at to use that specialization.  This removes some
manual reference counting and simplifies the code.

gdb/ChangeLog
2020-12-11  Tom Tromey  <tom@tromey.com>

	* inline-frame.c (stopped_by_user_bp_inline_frame): Update.
	* ada-lang.c (check_status_exception): Update.
	* breakpoint.c (free_bp_location): Remove.
	(decref_bp_location): Use bp_location_ref_policy.
	(bpstats::bpstats): Don't call incref_bp_location.
	(bpstats::~bpstats): Remove.
	(bpstats::bpstats): Update.
	(bpstat_check_watchpoint, bpstat_check_breakpoint_conditions)
	(bp_location::bp_location): Update.
	(incref_bp_location): Remove.
	(bkpt_print_it): Update.
	* breakpoint.h (class bp_location): Derive from
	refcounted_object.
	(struct bpstats): Remove destructor.
	<bp_location_at>: Now a bp_location_ref_ptr.
	<refc>: Remove.
	(bp_location_ref_ptr): New typedef.
	(struct bp_location_ref_policy): New.

5 files changed, 53 insertions, 45 deletions

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 691e583..61997f6 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,5 +1,26 @@
 2020-12-11  Tom Tromey  <tom@tromey.com>
 
+	* inline-frame.c (stopped_by_user_bp_inline_frame): Update.
+	* ada-lang.c (check_status_exception): Update.
+	* breakpoint.c (free_bp_location): Remove.
+	(decref_bp_location): Use bp_location_ref_policy.
+	(bpstats::bpstats): Don't call incref_bp_location.
+	(bpstats::~bpstats): Remove.
+	(bpstats::bpstats): Update.
+	(bpstat_check_watchpoint, bpstat_check_breakpoint_conditions)
+	(bp_location::bp_location): Update.
+	(incref_bp_location): Remove.
+	(bkpt_print_it): Update.
+	* breakpoint.h (class bp_location): Derive from
+	refcounted_object.
+	(struct bpstats): Remove destructor.
+	<bp_location_at>: Now a bp_location_ref_ptr.
+	<refc>: Remove.
+	(bp_location_ref_ptr): New typedef.
+	(struct bp_location_ref_policy): New.
+
+2020-12-11  Tom Tromey  <tom@tromey.com>
+
 	* thread.c (class scoped_inc_dec_ref): Remove.
 	(tp_array_compar_ascending, tp_array_compar_descending): Change
 	parameter types.
diff --git a/gdb/ada-lang.c b/gdb/ada-lang.c
index 39546de..b41d2bf 100644
--- a/gdb/ada-lang.c
+++ b/gdb/ada-lang.c
@@ -12255,7 +12255,7 @@ should_stop_exception (const struct bp_location *bl)
 static void
 check_status_exception (bpstat bs)
 {
-  bs->stop = should_stop_exception (bs->bp_location_at);
+  bs->stop = should_stop_exception (bs->bp_location_at.get ());
 }
 
 /* Implement the PRINT_IT method in the breakpoint_ops structure
diff --git a/gdb/breakpoint.c b/gdb/breakpoint.c
index baf80b6..933fe90 100644
--- a/gdb/breakpoint.c
+++ b/gdb/breakpoint.c
@@ -172,8 +172,6 @@ static int hw_watchpoint_used_count_others (struct breakpoint *except,
 static void enable_breakpoint_disp (struct breakpoint *, enum bpdisp,
 				    int count);
 
-static void free_bp_location (struct bp_location *loc);
-static void incref_bp_location (struct bp_location *loc);
 static void decref_bp_location (struct bp_location **loc);
 
 static struct bp_location *allocate_bp_location (struct breakpoint *bpt);
@@ -4242,15 +4240,6 @@ is_catchpoint (struct breakpoint *b)
   return (b->type == bp_catchpoint);
 }
 
-/* Frees any storage that is part of a bpstat.  Does not walk the
-   'next' chain.  */
-
-bpstats::~bpstats ()
-{
-  if (bp_location_at != NULL)
-    decref_bp_location (&bp_location_at);
-}
-
 /* Clear a bpstat so that it says we are not at any breakpoint.
    Also free any storage that is part of a bpstat.  */
 
@@ -4283,7 +4272,6 @@ bpstats::bpstats (const bpstats &other)
 {
   if (other.old_val != NULL)
     old_val = release_value (value_copy (other.old_val.get ()));
-  incref_bp_location (bp_location_at);
 }
 
 /* Return a copy of a bpstat.  Like "bs1 = bs2" but all storage that
@@ -4768,21 +4756,19 @@ breakpoint_cond_eval (expression *exp)
 
 bpstats::bpstats (struct bp_location *bl, bpstat **bs_link_pointer)
   : next (NULL),
-    bp_location_at (bl),
+    bp_location_at (bp_location_ref_ptr::new_reference (bl)),
     breakpoint_at (bl->owner),
     commands (NULL),
     print (0),
     stop (0),
     print_it (print_it_normal)
 {
-  incref_bp_location (bl);
   **bs_link_pointer = this;
   *bs_link_pointer = &next;
 }
 
 bpstats::bpstats ()
   : next (NULL),
-    bp_location_at (NULL),
     breakpoint_at (NULL),
     commands (NULL),
     print (0),
@@ -5060,7 +5046,7 @@ bpstat_check_watchpoint (bpstat bs)
   struct watchpoint *b;
 
   /* BS is built for existing struct breakpoint.  */
-  bl = bs->bp_location_at;
+  bl = bs->bp_location_at.get ();
   gdb_assert (bl != NULL);
   b = (struct watchpoint *) bs->breakpoint_at;
   gdb_assert (b != NULL);
@@ -5236,7 +5222,7 @@ bpstat_check_breakpoint_conditions (bpstat bs, thread_info *thread)
   gdb_assert (bs->stop);
 
   /* BS is built for existing struct breakpoint.  */
-  bl = bs->bp_location_at;
+  bl = bs->bp_location_at.get ();
   gdb_assert (bl != NULL);
   b = bs->breakpoint_at;
   gdb_assert (b != NULL);
@@ -7101,7 +7087,7 @@ bp_location::bp_location (breakpoint *owner, bp_loc_type type)
       || this->loc_type == bp_loc_hardware_breakpoint)
     mark_breakpoint_location_modified (this);
 
-  this->refc = 1;
+  incref ();
 }
 
 bp_location::bp_location (breakpoint *owner)
@@ -7118,30 +7104,13 @@ allocate_bp_location (struct breakpoint *bpt)
   return bpt->ops->allocate_location (bpt);
 }
 
-static void
-free_bp_location (struct bp_location *loc)
-{
-  delete loc;
-}
-
-/* Increment reference count.  */
-
-static void
-incref_bp_location (struct bp_location *bl)
-{
-  ++bl->refc;
-}
-
 /* Decrement reference count.  If the reference count reaches 0,
    destroy the bp_location.  Sets *BLP to NULL.  */
 
 static void
 decref_bp_location (struct bp_location **blp)
 {
-  gdb_assert ((*blp)->refc > 0);
-
-  if (--(*blp)->refc == 0)
-    free_bp_location (*blp);
+  bp_location_ref_policy::decref (*blp);
   *blp = NULL;
 }
 
@@ -12680,7 +12649,7 @@ bkpt_print_it (bpstat bs)
 
   gdb_assert (bs->bp_location_at != NULL);
 
-  bl = bs->bp_location_at;
+  bl = bs->bp_location_at.get ();
   b = bs->breakpoint_at;
 
   bp_temp = b->disposition == disp_del;
diff --git a/gdb/breakpoint.h b/gdb/breakpoint.h
index 4a65dd2..2859552 100644
--- a/gdb/breakpoint.h
+++ b/gdb/breakpoint.h
@@ -29,6 +29,7 @@
 #include <vector>
 #include "gdbsupport/array-view.h"
 #include "gdbsupport/function-view.h"
+#include "gdbsupport/refcounted-object.h"
 #include "cli/cli-script.h"
 
 struct block;
@@ -311,7 +312,7 @@ enum bp_loc_type
   bp_loc_other			/* Miscellaneous...  */
 };
 
-class bp_location
+class bp_location : public refcounted_object
 {
 public:
   bp_location () = default;
@@ -329,9 +330,6 @@ public:
      the same parent breakpoint.  */
   bp_location *next = NULL;
 
-  /* The reference count.  */
-  int refc = 0;
-
   /* Type of this breakpoint location.  */
   bp_loc_type loc_type {};
 
@@ -510,6 +508,27 @@ public:
   const struct objfile *objfile = NULL;
 };
 
+/* A policy class for bp_location reference counting.  */
+struct bp_location_ref_policy
+{
+  static void incref (bp_location *loc)
+  {
+    loc->incref ();
+  }
+
+  static void decref (bp_location *loc)
+  {
+    gdb_assert (loc->refcount () > 0);
+    loc->decref ();
+    if (loc->refcount () == 0)
+      delete loc;
+  }
+};
+
+/* A gdb::ref_ptr that has been specialized for bp_location.  */
+typedef gdb::ref_ptr<bp_location, bp_location_ref_policy>
+     bp_location_ref_ptr;
+
 /* The possible return values for print_bpstat, print_it_normal,
    print_it_done, print_it_noop.  */
 enum print_stop_action
@@ -1130,7 +1149,6 @@ struct bpstats
   {
     bpstats ();
     bpstats (struct bp_location *bl, bpstat **bs_link_pointer);
-    ~bpstats ();
 
     bpstats (const bpstats &);
     bpstats &operator= (const bpstats &) = delete;
@@ -1155,7 +1173,7 @@ struct bpstats
        What this means is that we should not (in most cases) follow
        the `bpstat->bp_location->owner' link, but instead use the
        `breakpoint_at' field below.  */
-    struct bp_location *bp_location_at;
+    bp_location_ref_ptr bp_location_at;
 
     /* Breakpoint that caused the stop.  This is nullified if the
        breakpoint ends up being deleted.  See comments on
diff --git a/gdb/inline-frame.c b/gdb/inline-frame.c
index 92a7d56..439f363 100644
--- a/gdb/inline-frame.c
+++ b/gdb/inline-frame.c
@@ -313,7 +313,7 @@ stopped_by_user_bp_inline_frame (const block *frame_block, bpstat stop_chain)
       if (bpt != NULL
 	  && (user_breakpoint_p (bpt) || bpt->type == bp_until))
 	{
-	  bp_location *loc = s->bp_location_at;
+	  bp_location *loc = s->bp_location_at.get ();
 	  enum bp_loc_type t = loc->loc_type;
 
 	  if (t == bp_loc_software_breakpoint