Further adjustments to mark_object and friends.

Now the mark_object's stack is just 32 bytes on a 64-bit
system, which means extra 20% off the stack usage.
* alloc.c (mark_save_value): As before, refactored out from ...
(mark_object): ... adjusted user.  Also add comment.

1 files changed, 32 insertions, 22 deletions

diff --git a/src/alloc.c b/src/alloc.c
index 98a35853e02..a7446e6b708 100644
--- a/src/alloc.c
+++ b/src/alloc.c
@@ -6068,6 +6068,30 @@ mark_localized_symbol (struct Lisp_Symbol *ptr)
   mark_object (blv->defcell);
 }
 
+NO_INLINE /* To reduce stack depth in mark_object.  */
+static void
+mark_save_value (struct Lisp_Save_Value *ptr)
+{
+  /* If `save_type' is zero, `data[0].pointer' is the address
+     of a memory area containing `data[1].integer' potential
+     Lisp_Objects.  */
+  if (GC_MARK_STACK && ptr->save_type == SAVE_TYPE_MEMORY)
+    {
+      Lisp_Object *p = ptr->data[0].pointer;
+      ptrdiff_t nelt;
+      for (nelt = ptr->data[1].integer; nelt > 0; nelt--, p++)
+        mark_maybe_object (*p);
+    }
+  else
+    {
+      /* Find Lisp_Objects in `data[N]' slots and mark them.  */
+      int i;
+      for (i = 0; i < SAVE_VALUE_SLOTS; i++)
+        if (save_type (ptr, i) == SAVE_OBJECT)
+          mark_object (ptr->data[i].object);
+    }
+}
+
 /* Remove killed buffers or items whose car is a killed buffer from
    LIST, and mark other items.  Return changed LIST, which is marked.  */
 
@@ -6095,7 +6119,13 @@ mark_discard_killed_buffers (Lisp_Object list)
   return list;
 }
 
-/* Determine type of generic Lisp_Object and mark it accordingly.  */
+/* Determine type of generic Lisp_Object and mark it accordingly.
+
+   This function implements a straightforward depth-first marking
+   algorithm and so the recursion depth may be very high (a few
+   tens of thousands is not uncommon).  To minimize stack usage,
+   a few cold paths are moved out to NO_INLINE functions above.
+   In general, inlining them doesn't help you to gain more speed.  */
 
 void
 mark_object (Lisp_Object arg)
@@ -6363,27 +6393,7 @@ mark_object (Lisp_Object arg)
 
         case Lisp_Misc_Save_Value:
           XMISCANY (obj)->gcmarkbit = 1;
-          {
-            struct Lisp_Save_Value *ptr = XSAVE_VALUE (obj);
-            /* If `save_type' is zero, `data[0].pointer' is the address
-               of a memory area containing `data[1].integer' potential
-               Lisp_Objects.  */
-            if (GC_MARK_STACK && ptr->save_type == SAVE_TYPE_MEMORY)
-              {
-                Lisp_Object *p = ptr->data[0].pointer;
-                ptrdiff_t nelt;
-                for (nelt = ptr->data[1].integer; nelt > 0; nelt--, p++)
-                  mark_maybe_object (*p);
-              }
-            else
-              {
-                /* Find Lisp_Objects in `data[N]' slots and mark them.  */
-                int i;
-                for (i = 0; i < SAVE_VALUE_SLOTS; i++)
-                  if (save_type (ptr, i) == SAVE_OBJECT)
-                    mark_object (ptr->data[i].object);
-              }
-          }
+          mark_save_value (XSAVE_VALUE (obj));
           break;
 
         case Lisp_Misc_Overlay: