[Emacs-diffs] trunk r117289: Change object marking routines to minimize stack usage.

[Dmitry Antipov]

------------------------------------------------------------
revno: 117289
revision-id: address@hidden
parent: address@hidden
committer: Dmitry Antipov <address@hidden>
branch nick: trunk
timestamp: Sun 2014-06-08 19:06:03 +0400
message:
  Change object marking routines to minimize stack usage.
  This change moves a few cold paths from mark_object to NO_INLINE
  functions and adjusts symbol marking loop.  According to GCC 4.8.2
  -Wstack-usage, this reduces mark_object's stack usage from 80 to
  48 bytes on a 64-bit system.  For a long byte-force-recompile runs,
  stack usage at the mark phase is reduced up to 28%.  Surprisingly,
  it also gains up to 3% in speed (with default '-O2 -g3' flags).
  * alloc.c (mark_compiled, mark_localized_symbol): New functions,
  refactored out from ...
  (mark_object): ... adjusted user.  Also mark symbols in a tight
  inner loop.
  (mark_face_cache): Add NO_INLINE.
modified:
  src/ChangeLog                  changelog-20091113204419-o5vbwnq5f7feedwu-1438
  src/alloc.c                    alloc.c-20091113204419-o5vbwnq5f7feedwu-252

=== modified file 'src/ChangeLog'
--- a/src/ChangeLog     2014-06-08 00:35:27 +0000
+++ b/src/ChangeLog     2014-06-08 15:06:03 +0000
@@ -1,3 +1,18 @@
+2014-06-08  Dmitry Antipov  <address@hidden>
+
+       Change object marking routines to minimize stack usage.
+       This change moves a few cold paths from mark_object to NO_INLINE
+       functions and adjusts symbol marking loop.  According to GCC 4.8.2
+       -Wstack-usage, this reduces mark_object's stack usage from 80 to
+       48 bytes on a 64-bit system.  For a long byte-force-recompile runs,
+       stack usage at the mark phase is reduced up to 28%.  Surprisingly,
+       it also gains up to 3% in speed (with default '-O2 -g3' flags).
+       * alloc.c (mark_compiled, mark_localized_symbol): New functions,
+       refactored out from ...
+       (mark_object): ... adjusted user.  Also mark symbols in a tight
+       inner loop.
+       (mark_face_cache): Add NO_INLINE.
+
 2014-06-08  Eli Zaretskii  <address@hidden>
 
        * sysdep.c (reset_sys_modes): Use cursorX, not curX, as the latter

=== modified file 'src/alloc.c'
--- a/src/alloc.c       2014-06-02 00:18:22 +0000
+++ b/src/alloc.c       2014-06-08 15:06:03 +0000
@@ -5974,6 +5974,19 @@
     }
 }
 
+NO_INLINE /* To reduce stack depth in mark_object.  */
+static Lisp_Object
+mark_compiled (struct Lisp_Vector *ptr)
+{
+  int i, size = ptr->header.size & PSEUDOVECTOR_SIZE_MASK;
+  
+  VECTOR_MARK (ptr);
+  for (i = 0; i < size; i++)
+    if (i != COMPILED_CONSTANTS)
+      mark_object (ptr->contents[i]);
+  return size > COMPILED_CONSTANTS ? ptr->contents[COMPILED_CONSTANTS] : Qnil;
+}
+
 /* Mark the chain of overlays starting at PTR.  */
 
 static void
@@ -6014,6 +6027,7 @@
 
 /* Mark Lisp faces in the face cache C.  */
 
+NO_INLINE /* To reduce stack depth in mark_object.  */
 static void
 mark_face_cache (struct face_cache *c)
 {
@@ -6036,6 +6050,24 @@
     }
 }
 
+NO_INLINE /* To reduce stack depth in mark_object.  */
+static void
+mark_localized_symbol (struct Lisp_Symbol *ptr)
+{
+  struct Lisp_Buffer_Local_Value *blv = SYMBOL_BLV (ptr);
+  Lisp_Object where = blv->where;
+  /* If the value is set up for a killed buffer or deleted
+     frame, restore it's global binding.  If the value is
+     forwarded to a C variable, either it's not a Lisp_Object
+     var, or it's staticpro'd already.  */
+  if ((BUFFERP (where) && !BUFFER_LIVE_P (XBUFFER (where)))
+      || (FRAMEP (where) && !FRAME_LIVE_P (XFRAME (where))))
+    swap_in_global_binding (ptr);
+  mark_object (blv->where);
+  mark_object (blv->valcell);
+  mark_object (blv->defcell);
+}
+
 /* Remove killed buffers or items whose car is a killed buffer from
    LIST, and mark other items.  Return changed LIST, which is marked.  */
 
@@ -6180,22 +6212,13 @@
            break;
 
          case PVEC_COMPILED:
-           { /* We could treat this just like a vector, but it is better
-                to save the COMPILED_CONSTANTS element for last and avoid
-                recursion there.  */
-             int size = ptr->header.size & PSEUDOVECTOR_SIZE_MASK;
-             int i;
-
-             VECTOR_MARK (ptr);
-             for (i = 0; i < size; i++)
-               if (i != COMPILED_CONSTANTS)
-                 mark_object (ptr->contents[i]);
-             if (size > COMPILED_CONSTANTS)
-               {
-                 obj = ptr->contents[COMPILED_CONSTANTS];
-                 goto loop;
-               }
-           }
+           /* Although we could treat this just like a vector, mark_compiled
+              returns the COMPILED_CONSTANTS element, which is marked at the
+              next iteration of goto-loop here.  This is done to avoid a few
+              recursive calls to mark_object.  */
+           obj = mark_compiled (ptr);
+           if (!NILP (obj))
+             goto loop;
            break;
 
          case PVEC_FRAME:
@@ -6283,8 +6306,7 @@
     case Lisp_Symbol:
       {
        register struct Lisp_Symbol *ptr = XSYMBOL (obj);
-       struct Lisp_Symbol *ptrx;
-
+      nextsym:
        if (ptr->gcmarkbit)
          break;
        CHECK_ALLOCATED_AND_LIVE (live_symbol_p);
@@ -6304,21 +6326,8 @@
              break;
            }
          case SYMBOL_LOCALIZED:
-           {
-             struct Lisp_Buffer_Local_Value *blv = SYMBOL_BLV (ptr);
-             Lisp_Object where = blv->where;
-             /* If the value is set up for a killed buffer or deleted
-                frame, restore it's global binding.  If the value is
-                forwarded to a C variable, either it's not a Lisp_Object
-                var, or it's staticpro'd already.  */
-             if ((BUFFERP (where) && !BUFFER_LIVE_P (XBUFFER (where)))
-                 || (FRAMEP (where) && !FRAME_LIVE_P (XFRAME (where))))
-               swap_in_global_binding (ptr);
-             mark_object (blv->where);
-             mark_object (blv->valcell);
-             mark_object (blv->defcell);
-             break;
-           }
+           mark_localized_symbol (ptr);
+           break;
          case SYMBOL_FORWARDED:
            /* If the value is forwarded to a buffer or keyboard field,
               these are marked when we see the corresponding object.
@@ -6330,14 +6339,10 @@
        if (!PURE_POINTER_P (XSTRING (ptr->name)))
          MARK_STRING (XSTRING (ptr->name));
        MARK_INTERVAL_TREE (string_intervals (ptr->name));
-
+       /* Inner loop to mark next symbol in this bucket, if any.  */
        ptr = ptr->next;
        if (ptr)
-         {
-           ptrx = ptr;         /* Use of ptrx avoids compiler bug on Sun.  */
-           XSETSYMBOL (obj, ptrx);
-           goto loop;
-         }
+         goto nextsym;
       }
       break;