honor SPOT_BDD_TRACE

* spot/priv/bddalloc.cc: Add hooks on request.
* bin/man/spot-x.x, NEWS: Document the envvar.

NEWS

@@ -150,6 +150,10 @@ New in spot 2.3.5.dev (not yet released)
 
   - spot::sbacc() is now able to work on alternating automata.
 
+  - If the SPOT_BDD_TRACE envorinment variable is set, statistics
+    about BDD garbage collection and table resizing are shown.
+
+
   Python:
 
   - The 'spot.gen' package exports the functions from libspotgen.

bin/man/spot-x.x

@@ -39,6 +39,11 @@ This naive method tries to reduce the size of the automaton one state at a
 time. Note that it restarts all the encoding each time.
 
 [ENVIRONMENT VARIABLES]
+.TP
+\fBSPOT_BDD_TRACE\fR
+If this variable is set to any value, statistics about BDD garbage
+collection and resizing will be output on standard error.
+
 .TP
 \fBSPOT_DEFAULT_FORMAT\fR
 Set to a value of \fBdot\fR or \fBhoa\fR to override the default

spot/priv/bddalloc.cc

 // -*- coding: utf-8 -*-
-// Copyright (C) 2007, 2011, 2014, 2015 Laboratoire de Recherche et
+// Copyright (C) 2007, 2011, 2014, 2015, 2017 Laboratoire de Recherche et
 // Développement de l'Epita (LRDE).
 // Copyright (C) 2003, 2004, 2006, 2007 Laboratoire d'Informatique de
 // Paris 6 (LIP6), département Systèmes Répartis Coopératifs (SRC),
@@ -22,6 +22,8 @@
 
 #include <bddx.h>
 #include <cassert>
+#include <cstdlib>
+#include <ctime>
 #include "spot/priv/bddalloc.hh"
 
 namespace spot
@@ -29,6 +31,37 @@ namespace spot
 
   bool bdd_allocator::initialized = false;
 
+  static void show_bdd_stats()
+  {
+    bddStat s;
+    bdd_stats(&s);
+    std::cerr << "spot: BDD stats: produced=" << s.produced
+              << " nodenum=" << s.nodenum
+              << " freenodes=" << s.freenodes
+              << " (" << (s.freenodes * 100 / s.nodenum)
+              << "%) minfreenodes=" << s.minfreenodes
+              << "% varnum=" << s.varnum
+              << " cachesize=" << s.cachesize
+              << " hashsize=" << s.hashsize
+              << " gbcnum=" << s.gbcnum
+              << '\n';
+  }
+
+  static void resize_handler(int oldsize, int newsize)
+  {
+    std::cerr << "spot: BDD resize "
+              << oldsize << " -> " << newsize << '\n';
+  }
+
+  static void gbc_handler(int pre, bddGbcStat *s)
+  {
+    if (!pre)
+      std::cerr << "spot: BDD GC #" << s->num
+                << " in " << ((float)s->time)/CLOCKS_PER_SEC << "s / "
+                << ((float)s->sumtime)/CLOCKS_PER_SEC << "s total\n";
+    show_bdd_stats();
+  }
+
   bdd_allocator::bdd_allocator()
   {
     initialize();
@@ -49,14 +82,25 @@ namespace spot
     // the library is solving.  It would be nice to allow users
     // to tune this.  By the meantime, we take the typical values
     // for large examples advocated by the BuDDy manual.
-    bdd_init(1000000, 10000);
+    bdd_init(1 << 19, 2);
+    bdd_setcacheratio(40);
     bdd_setvarnum(2);
+    // When the node table is full, add 2**19 nodes; this requires 10MB.
+    bdd_setmaxincrease(1 << 19);
     // Disable the default GC handler.  (Note that this will only be
     // done if Buddy is initialized by Spot.  Otherwise we prefer not
     // to overwrite a handler that might have been set by the user.)
-    bdd_gbc_hook(nullptr);
-    // When the node time is full, add 500000 nodes, i.e., 10MB.
-    bdd_setmaxincrease(500000);
+    if (getenv("SPOT_BDD_TRACE"))
+      {
+        bdd_gbc_hook(gbc_handler);
+        bdd_resize_hook(resize_handler);
+        std::cerr << "spot: BDD package initialized\n";
+        show_bdd_stats();
+      }
+    else
+      {
+        bdd_gbc_hook(nullptr);
+      }
   }
 
   void