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, 7 insertions, 2 deletions

diff --git a/src/lisp.h b/src/lisp.h
index b7e5d9e3761..af3f587222d 100644
--- a/src/lisp.h
+++ b/src/lisp.h
@@ -3188,6 +3188,7 @@ enum specbind_tag {
   SPECPDL_UNWIND,               /* An unwind_protect function on Lisp_Object.  */
   SPECPDL_UNWIND_PTR,           /* Likewise, on void *.  */
   SPECPDL_UNWIND_INT,           /* Likewise, on int.  */
+  SPECPDL_UNWIND_EXCURSION,     /* Likewise, on an execursion.  */
   SPECPDL_UNWIND_VOID,          /* Likewise, with no arg.  */
   SPECPDL_BACKTRACE,            /* An element of the backtrace.  */
   SPECPDL_LET,                  /* A plain and simple dynamic let-binding.  */
@@ -3216,6 +3217,10 @@ union specbinding
     } unwind_int;
     struct {
       ENUM_BF (specbind_tag) kind : CHAR_BIT;
+      Lisp_Object marker, window;
+    } unwind_excursion;
+    struct {
+      ENUM_BF (specbind_tag) kind : CHAR_BIT;
       void (*func) (void);
     } unwind_void;
     struct {
@@ -4106,9 +4111,9 @@ extern void mark_threads (void);
 
 /* Defined in editfns.c.  */
 extern void insert1 (Lisp_Object);
-extern Lisp_Object save_excursion_save (void);
+extern void save_excursion_save (union specbinding *);
+extern void save_excursion_restore (Lisp_Object, Lisp_Object);
 extern Lisp_Object save_restriction_save (void);
-extern void save_excursion_restore (Lisp_Object);
 extern void save_restriction_restore (Lisp_Object);
 extern _Noreturn void time_overflow (void);
 extern Lisp_Object make_buffer_string (ptrdiff_t, ptrdiff_t, bool);