added 'cachemiss' field to prototype to avoid wasting time checking

hits that fail too often

lfunc.c

@@ -1,5 +1,5 @@
 /*
-** $Id: lfunc.c,v 2.46 2017/04/06 13:08:56 roberto Exp roberto $
+** $Id: lfunc.c,v 2.47 2017/04/11 18:41:09 roberto Exp roberto $
 ** Auxiliary functions to manipulate prototypes and closures
 ** See Copyright Notice in lua.h
 */
@@ -115,6 +115,7 @@ Proto *luaF_newproto (lua_State *L) {
   f->sizep = 0;
   f->code = NULL;
   f->cache = NULL;
+  f->cachemiss = 0;
   f->sizecode = 0;
   f->lineinfo = NULL;
   f->sizelineinfo = 0;

lgc.c

@@ -1,5 +1,5 @@
 /*
-** $Id: lgc.c,v 2.225 2017/04/24 16:59:26 roberto Exp $
+** $Id: lgc.c,v 2.226 2017/04/24 17:52:18 roberto Exp roberto $
 ** Garbage Collector
 ** See Copyright Notice in lua.h
 */
@@ -485,6 +485,7 @@ static int traverseproto (global_State *g, Proto *f) {
   int i;
   if (f->cache && iswhite(f->cache))
     f->cache = NULL;  /* allow cache to be collected */
+  f->cachemiss = 0;  /* restart counting */
   markobjectN(g, f->source);
   for (i = 0; i < f->sizek; i++)  /* mark literals */
     markvalue(g, &f->k[i]);

lobject.h

@@ -1,5 +1,5 @@
 /*
-** $Id: lobject.h,v 2.118 2017/04/11 18:41:09 roberto Exp roberto $
+** $Id: lobject.h,v 2.119 2017/04/24 18:06:12 roberto Exp roberto $
 ** Type definitions for Lua objects
 ** See Copyright Notice in lua.h
 */
@@ -410,6 +410,7 @@ typedef struct Proto {
   lu_byte numparams;  /* number of fixed parameters */
   lu_byte is_vararg;
   lu_byte maxstacksize;  /* number of registers needed by this function */
+  lu_byte cachemiss;  /* count for successive misses for 'cache' field */
   int sizeupvalues;  /* size of 'upvalues' */
   int sizek;  /* size of 'k' */
   int sizecode;

lvm.c

@@ -1,5 +1,5 @@
 /*
-** $Id: lvm.c,v 2.273 2017/04/26 17:46:52 roberto Exp roberto $
+** $Id: lvm.c,v 2.274 2017/04/28 20:57:45 roberto Exp roberto $
 ** Lua virtual machine
 ** See Copyright Notice in lua.h
 */
@@ -618,6 +618,7 @@ static LClosure *getcached (Proto *p, UpVal **encup, StkId base) {
       if (c->upvals[i]->v != v)
         return NULL;  /* wrong upvalue; cannot reuse closure */
     }
+    p->cachemiss = 0;  /* got a hit */
   }
   return c;  /* return cached closure (or NULL if no cached closure) */
 }
@@ -644,8 +645,13 @@ static void pushclosure (lua_State *L, Proto *p, UpVal **encup, StkId base,
       ncl->upvals[i] = encup[uv[i].idx];
     /* new closure is white, so we do not need a barrier here */
   }
-  if (!isblack(p))  /* cache will not break GC invariant? */
-    p->cache = ncl;  /* save it on cache for reuse */
+  if (p->cachemiss >= 10)  /* too many missings? */
+    p->cache = NULL;  /* give up cache */
+  else {
+    if (!isblack(p))  /* cache will not break GC invariant? */
+      p->cache = ncl;  /* save it on cache for reuse */
+    p->cachemiss++;
+  }
 }