Cheaper fluid-ref cache

* libguile/cache-internal.h (struct scm_cache_entry): Add needs_flush
  member.
  (scm_cache_evict_1): Clear needs_flush on newly evicted entry.
  (scm_cache_insert): Propagate needs_flush to new entry.
* libguile/fluids.c (restore_dynamic_state): Mark all restored entries
  as needing a flush.
  (save_dynamic_state): Only cons on "needs_flush" entries to the
  resulting dynamic state.  The result is the same as before but
  avoiding the refq on the weak table.
  (fluid_set_x): Propagate needs_flush down to the cache.
  (fluid_ref): When adding entry to cache, use needs_flush==0.
  (scm_fluid_set_x, scm_fluid_unset_x, scm_swap_fluid, swap_fluid): Use
  needs_flush==1.

2 files changed, 22 insertions, 14 deletions

diff --git a/libguile/cache-internal.h b/libguile/cache-internal.h
index fc1e3c139..88bb24af0 100644
--- a/libguile/cache-internal.h
+++ b/libguile/cache-internal.h
@@ -37,6 +37,7 @@ struct scm_cache_entry
 {
   scm_t_bits key;
   scm_t_bits value;
+  int needs_flush;
 };
 
 #define SCM_CACHE_SIZE 8
@@ -73,6 +74,7 @@ scm_cache_evict_1 (struct scm_cache *cache, struct scm_cache_entry *evicted)
            sizeof (cache->entries[0]) * idx);
   cache->entries[0].key = 0;
   cache->entries[0].value = 0;
+  cache->entries[0].needs_flush = 0;
 }
 
 static inline struct scm_cache_entry*
@@ -89,7 +91,7 @@ scm_cache_lookup (struct scm_cache *cache, SCM k)
 
 static inline void
 scm_cache_insert (struct scm_cache *cache, SCM k, SCM v,
-                  struct scm_cache_entry *evicted)
+                  struct scm_cache_entry *evicted, int needs_flush)
 {
   struct scm_cache_entry *entry;
 
@@ -99,6 +101,7 @@ scm_cache_insert (struct scm_cache *cache, SCM k, SCM v,
   if (entry->key == SCM_UNPACK (k))
     {
       entry->value = SCM_UNPACK (v);
+      entry->needs_flush = needs_flush;
       return;
     }
   memmove (cache->entries,
@@ -106,6 +109,7 @@ scm_cache_insert (struct scm_cache *cache, SCM k, SCM v,
            (entry - cache->entries) * sizeof (*entry));
   entry->key = SCM_UNPACK (k);
   entry->value = SCM_UNPACK (v);
+  entry->needs_flush = needs_flush;
 }
 
 #endif /* SCM_CACHE_INTERNAL_H */
diff --git a/libguile/fluids.c b/libguile/fluids.c
index 7daad7781..5b42ccb6d 100644
--- a/libguile/fluids.c
+++ b/libguile/fluids.c
@@ -114,10 +114,11 @@ restore_dynamic_state (SCM saved, scm_t_dynamic_state *state)
         {
           entry->key = SCM_UNPACK (SCM_CAAR (saved));
           entry->value = SCM_UNPACK (SCM_CDAR (saved));
+          entry->needs_flush = 1;
           saved = scm_cdr (saved);
         }
       else
-        entry->key = entry->value = 0;
+        entry->key = entry->value = entry->needs_flush = 0;
     }
   state->values = saved;
   state->has_aliased_values = 1;
@@ -133,9 +134,7 @@ save_dynamic_state (scm_t_dynamic_state *state)
       struct scm_cache_entry *entry = &state->cache.entries[slot];
       SCM key = SCM_PACK (entry->key);
       SCM value = SCM_PACK (entry->value);
-      if (entry->key &&
-          !scm_is_eq (scm_weak_table_refq (state->values, key, SCM_UNDEFINED),
-                      value))
+      if (entry->key && entry->needs_flush)
         {
           if (state->has_aliased_values)
             saved = scm_acons (key, value, saved);
@@ -249,7 +248,8 @@ scm_is_fluid (SCM obj)
 }
 
 static void
-fluid_set_x (scm_t_dynamic_state *dynamic_state, SCM fluid, SCM value)
+fluid_set_x (scm_t_dynamic_state *dynamic_state, SCM fluid, SCM value,
+             int needs_flush)
 {
   struct scm_cache_entry *entry;
   struct scm_cache_entry evicted = { 0, 0 };
@@ -257,13 +257,17 @@ fluid_set_x (scm_t_dynamic_state *dynamic_state, SCM fluid, SCM value)
   entry = scm_cache_lookup (&dynamic_state->cache, fluid);
   if (scm_is_eq (SCM_PACK (entry->key), fluid))
     {
-      entry->value = SCM_UNPACK (value);
+      if (SCM_UNPACK (value) != entry->value)
+        {
+          entry->needs_flush = 1;
+          entry->value = SCM_UNPACK (value);
+        }
       return;
     }
 
-  scm_cache_insert (&dynamic_state->cache, fluid, value, &evicted);
+  scm_cache_insert (&dynamic_state->cache, fluid, value, &evicted, 1);
 
-  if (evicted.key != 0)
+  if (evicted.key != 0 && evicted.needs_flush)
     {
       fluid = SCM_PACK (evicted.key);
       value = SCM_PACK (evicted.value);
@@ -300,7 +304,7 @@ fluid_ref (scm_t_dynamic_state *dynamic_state, SCM fluid)
         val = SCM_I_FLUID_DEFAULT (fluid);
 
       /* Cache this lookup.  */
-      fluid_set_x (dynamic_state, fluid, val);
+      fluid_set_x (dynamic_state, fluid, val, 0);
     }
 
   return val;
@@ -355,7 +359,7 @@ SCM_DEFINE (scm_fluid_set_x, "fluid-set!", 2, 0, 0,
 #define FUNC_NAME s_scm_fluid_set_x
 {
   SCM_VALIDATE_FLUID (1, fluid);
-  fluid_set_x (SCM_I_CURRENT_THREAD->dynamic_state, fluid, value);
+  fluid_set_x (SCM_I_CURRENT_THREAD->dynamic_state, fluid, value, 1);
   return SCM_UNSPECIFIED;
 }
 #undef FUNC_NAME
@@ -369,7 +373,7 @@ SCM_DEFINE (scm_fluid_unset_x, "fluid-unset!", 1, 0, 0,
      suite demands it, but I would prefer not to.  */
   SCM_VALIDATE_FLUID (1, fluid);
   SCM_SET_CELL_OBJECT_1 (fluid, SCM_UNDEFINED);
-  fluid_set_x (SCM_I_CURRENT_THREAD->dynamic_state, fluid, SCM_UNDEFINED);
+  fluid_set_x (SCM_I_CURRENT_THREAD->dynamic_state, fluid, SCM_UNDEFINED, 1);
   return SCM_UNSPECIFIED;
 }
 #undef FUNC_NAME
@@ -397,7 +401,7 @@ void
 scm_swap_fluid (SCM fluid, SCM value_box, scm_t_dynamic_state *dynstate)
 {
   SCM val = fluid_ref (dynstate, fluid);
-  fluid_set_x (dynstate, fluid, SCM_VARIABLE_REF (value_box));
+  fluid_set_x (dynstate, fluid, SCM_VARIABLE_REF (value_box), 1);
   SCM_VARIABLE_SET (value_box, val);
 }
   
@@ -474,7 +478,7 @@ swap_fluid (SCM data)
   scm_t_dynamic_state *dynstate = SCM_I_CURRENT_THREAD->dynamic_state;
   SCM f = SCM_CAR (data);
   SCM t = fluid_ref (dynstate, f);
-  fluid_set_x (dynstate, f, SCM_CDR (data));
+  fluid_set_x (dynstate, f, SCM_CDR (data), 1);
   SCM_SETCDR (data, t);
 }