Avoid allocating Lisp_Save_Value for excursions

* src/editfns.c (save_excursion_save): New arg PDL,
specifying where to save the state.  All uses changed.
(save_excursion_restore): Args are now the marker and info
rather than a pointer to a Lisp_Save_Value containing them.
All uses changed.
* src/eval.c (default_toplevel_binding, Fbacktrace__locals):
Treat excursions like other miscellaneous pdl types.
(record_unwind_protect_excursion): Save data directly
into the pdl rather than creating an object on the heap.
This avoids the need to allocate and free an object.
(do_one_unbind, backtrace_eval_unrewind):
Unwind excursions directly.
(mark_specpdl): Mark excursions directly.
* src/lisp.h (SPECPDL_UNWIND_EXCURSION): New constant.
(union specbinding): New member unwind_excursion.

1 files changed, 27 insertions, 11 deletions

diff --git a/src/eval.c b/src/eval.c
index 5c7cb3196a6..dded16bed55 100644
--- a/src/eval.c
+++ b/src/eval.c
@@ -675,6 +675,7 @@ default_toplevel_binding (Lisp_Object symbol)
         case SPECPDL_UNWIND:
         case SPECPDL_UNWIND_PTR:
         case SPECPDL_UNWIND_INT:
+        case SPECPDL_UNWIND_EXCURSION:
         case SPECPDL_UNWIND_VOID:
         case SPECPDL_BACKTRACE:
         case SPECPDL_LET_LOCAL:
@@ -3427,7 +3428,9 @@ record_unwind_protect_int (void (*function) (int), int arg)
 void
 record_unwind_protect_excursion (void)
 {
-  record_unwind_protect (save_excursion_restore, save_excursion_save ());
+  specpdl_ptr->unwind_excursion.kind = SPECPDL_UNWIND_EXCURSION;
+  save_excursion_save (specpdl_ptr);
+  grow_specpdl ();
 }
 
 void
@@ -3475,6 +3478,10 @@ do_one_unbind (union specbinding *this_binding, bool unwinding,
     case SPECPDL_UNWIND_VOID:
       this_binding->unwind_void.func ();
       break;
+    case SPECPDL_UNWIND_EXCURSION:
+      save_excursion_restore (this_binding->unwind_excursion.marker,
+                              this_binding->unwind_excursion.window);
+      break;
     case SPECPDL_BACKTRACE:
       break;
     case SPECPDL_LET:
@@ -3749,18 +3756,21 @@ backtrace_eval_unrewind (int distance)
              unwind_protect, but the problem is that we don't know how to
              rewind them afterwards.  */
         case SPECPDL_UNWIND:
-          {
-            Lisp_Object oldarg = tmp->unwind.arg;
-            if (tmp->unwind.func == set_buffer_if_live)
+          if (tmp->unwind.func == set_buffer_if_live)
+            {
+              Lisp_Object oldarg = tmp->unwind.arg;
               tmp->unwind.arg = Fcurrent_buffer ();
-            else if (tmp->unwind.func == save_excursion_restore)
-              tmp->unwind.arg = save_excursion_save ();
-            else
-              break;
-            tmp->unwind.func (oldarg);
-            break;
+              set_buffer_if_live (oldarg);
+            }
+          break;
+        case SPECPDL_UNWIND_EXCURSION:
+          {
+            Lisp_Object marker = tmp->unwind_excursion.marker;
+            Lisp_Object window = tmp->unwind_excursion.window;
+            save_excursion_save (tmp);
+            save_excursion_restore (marker, window);
           }
-
+          break;
         case SPECPDL_UNWIND_PTR:
         case SPECPDL_UNWIND_INT:
         case SPECPDL_UNWIND_VOID:
@@ -3895,6 +3905,7 @@ NFRAMES and BASE specify the activation frame to use, as in `backtrace-frame'.
           case SPECPDL_UNWIND:
           case SPECPDL_UNWIND_PTR:
           case SPECPDL_UNWIND_INT:
+          case SPECPDL_UNWIND_EXCURSION:
           case SPECPDL_UNWIND_VOID:
           case SPECPDL_BACKTRACE:
             break;
@@ -3924,6 +3935,11 @@ mark_specpdl (union specbinding *first, union specbinding *ptr)
           mark_object (specpdl_arg (pdl));
           break;
 
+        case SPECPDL_UNWIND_EXCURSION:
+          mark_object (pdl->unwind_excursion.marker);
+          mark_object (pdl->unwind_excursion.window);
+          break;
+
         case SPECPDL_BACKTRACE:
           {
             ptrdiff_t nargs = backtrace_nargs (pdl);