Patch for speeding up the debugging evaluator by a factor of 600

[Matthias Koeppe <mkoeppe@mail.math.uni-magdeburg.de>]

I am using Guile 1.6.4 with GOOPS and about 4000 primitive procedures.
In this setting, when I try to TRACE a function, the debugging
evaluator becomes unusably slow.  I illustrate this on a call to
APROPOS:

        guile> (time (apropos "doesntexist"))
        ;; Evaluation took:
        ;;   0.05 seconds of real time
        ;;   0.04 seconds of user time
        ;;   0 seconds of system time
        guile> (trace load)
        $3 = (load-module)
        guile> (time (apropos "doesntexist"))
        ;; Evaluation took:
        ;;   32.02 seconds of real time
        ;;   32.02 seconds of user time
        ;;   0 seconds of system time

I found out that a one-line change by Mikael Djurfeldt in CVS HEAD
makes a major speed-up:

2003-03-06  Mikael Djurfeldt  <djurfeldt@nada.kth.se>

	* procprop.c (scm_stand_in_scm_proc): Use scm_assq instead of
	scm_assoc.

--- procprop.c.~1.37.2.2.~	2002-03-21 17:53:18.000000000 +0100
+++ procprop.c	2004-07-08 19:43:16.746126000 +0200
@@ -160,7 +160,7 @@
 scm_stand_in_scm_proc(SCM proc)
 {
   SCM answer;
-  answer = scm_assoc (proc, scm_stand_in_procs);
+  answer = scm_assq (proc, scm_stand_in_procs);
   if (SCM_FALSEP (answer))
     {
       answer = scm_closure (scm_list_2 (SCM_EOL, SCM_BOOL_F), SCM_EOL);

With this change applied to branch_release_1_6, I get:

        guile> (trace load)
        $3 = (load-module)
        guile> (time (apropos "doesntexist"))
        ;; Evaluation took:
        ;;   1.17 seconds of real time
        ;;   1.17 seconds of user time
        ;;   0 seconds of system time

A 30-fold speedup, but still much slower than the untraced version.
The scm_assq is still the bottleneck (90% of the run time).  The real
fix is to use a hash table rather than an alist.  Here is a patch
(against the stable branch) that does this:

Index: libguile/gc.c
===================================================================
RCS file: /cvsroot/guile/guile/guile-core/libguile/gc.c,v
retrieving revision 1.208.2.11
diff -u -p -r1.208.2.11 gc.c
--- libguile/gc.c	1 Oct 2003 19:51:43 -0000	1.208.2.11
+++ libguile/gc.c	8 Jul 2004 19:28:45 -0000
@@ -2827,7 +2827,7 @@ scm_init_storage ()
 #endif
 #endif

-  scm_stand_in_procs = SCM_EOL;
+  scm_stand_in_procs = scm_c_make_hash_table (257);
   scm_permobjs = SCM_EOL;
   scm_protects = scm_c_make_hash_table (31);
   scm_gc_registered_roots = scm_c_make_hash_table (31);
Index: libguile/procprop.c
===================================================================
RCS file: /cvsroot/guile/guile/guile-core/libguile/procprop.c,v
retrieving revision 1.37.2.2
diff -u -p -r1.37.2.2 procprop.c
--- libguile/procprop.c	14 Mar 2002 05:26:15 -0000	1.37.2.2
+++ libguile/procprop.c	8 Jul 2004 19:28:45 -0000
@@ -52,6 +52,7 @@
 #include "libguile/smob.h"
 #include "libguile/root.h"
 #include "libguile/vectors.h"
+#include "libguile/hashtab.h"

 #include "libguile/validate.h"
 #include "libguile/procprop.h"
@@ -159,15 +160,16 @@ scm_i_procedure_arity (SCM proc)
 static SCM
 scm_stand_in_scm_proc(SCM proc)
 {
-  SCM answer;
-  answer = scm_assoc (proc, scm_stand_in_procs);
-  if (SCM_FALSEP (answer))
+  SCM handle, answer;
+  handle = scm_hashq_get_handle (scm_stand_in_procs, proc);
+  if (SCM_FALSEP (handle))
     {
       answer = scm_closure (scm_list_2 (SCM_EOL, SCM_BOOL_F), SCM_EOL);
-      scm_stand_in_procs = scm_acons (proc, answer, scm_stand_in_procs);
+      scm_hashq_set_x (scm_stand_in_procs, proc, answer);
     }
-  else
-    answer = SCM_CDR (answer);
+  else {
+    answer = SCM_CDR(handle);
+  }
   return answer;
 }

With this patch, I get about the same timings as without tracing.

        guile> (trace load)
        $3 = (load-module)
        guile> (time (apropos "doesntexist"))
        ;; Evaluation took:
        ;;   0.05 seconds of real time
        ;;   0.05 seconds of user time
        ;;   0 seconds of system time 

Could someone please put the fix in CVS (stable branch and CVS HEAD)?
Thanks.

-- 
Matthias Koeppe -- http://www.math.uni-magdeburg.de/~mkoeppe


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