scratch/hash-table-perf 8811c5d81e7 27/35: Don't dump Qunbound

[Mattias Engdegård]

branch: scratch/hash-table-perf
commit 8811c5d81e71d75268f0d81cfcbbe93be8e0035e
Author: Mattias Engdegård <mattiase@acm.org>
Commit: Mattias Engdegård <mattiase@acm.org>

    Don't dump Qunbound
    
    The dumper uses a hash table to keep track of dumped objects but as
    this clashes with the use of Qunbound for marking unused hash table
    entries, don't dump that value at all.  The symbol name is fixed up
    after loading.
    
    An alternative solution would be to use a different unique value for
    unused entries.
    
    * src/pdumper.c (dump_object_needs_dumping_p): Skip Qunbound.
    (dump_vectorlike_generic): New function.
    (pdumper_load): Call it.
---
 src/fns.c     |  1 +
 src/pdumper.c | 19 ++++++++++++++++++-
 2 files changed, 19 insertions(+), 1 deletion(-)

diff --git a/src/fns.c b/src/fns.c
index a051a155723..48c0e603c5d 100644
--- a/src/fns.c
+++ b/src/fns.c
@@ -4812,6 +4812,7 @@ ptrdiff_t
 hash_put (struct Lisp_Hash_Table *h, Lisp_Object key, Lisp_Object value,
          hash_hash_t hash)
 {
+  eassert (!BASE_EQ (key, Qunbound));
   /* Increment count after resizing because resizing may fail.  */
   maybe_resize_hash_table (h);
   h->count++;
diff --git a/src/pdumper.c b/src/pdumper.c
index bc7d8fac5fe..3f6240a5076 100644
--- a/src/pdumper.c
+++ b/src/pdumper.c
@@ -1337,7 +1337,9 @@ dump_object_needs_dumping_p (Lisp_Object object)
      included in the dump despite all references to them being
      bitwise-invariant.  */
   return (!dump_object_self_representing_p (object)
-         || dump_object_emacs_ptr (object));
+         || (dump_object_emacs_ptr (object)
+             /* Don't dump Qunbound -- it's not a legal hash table key.  */
+             && !BASE_EQ (object, Qunbound)));
 }
 
 static void
@@ -2551,6 +2553,19 @@ dump_symbol (struct dump_context *ctx,
   return offset;
 }
 
+/* Give Qunbound its name.
+   All other symbols are dumped and loaded but not Qunbound because it
+   cannot be used as a key in a hash table.
+   FIXME: A better solution would be to use a value other than Qunbound
+   as a marker for unused entries in hash tables.  */
+static void
+pdumper_init_symbol_unbound (void)
+{
+  eassert (NILP (SYMBOL_NAME (Qunbound)));
+  const char *name = "unbound";
+  init_symbol (Qunbound, make_pure_c_string (name, strlen (name)));
+}
+
 static dump_off
 dump_vectorlike_generic (struct dump_context *ctx,
                         const union vectorlike_header *header)
@@ -5749,6 +5764,8 @@ pdumper_load (const char *dump_filename, char *argv0)
   for (int i = 0; i < nr_dump_hooks; ++i)
     dump_hooks[i] ();
 
+  pdumper_init_symbol_unbound ();
+
 #ifdef HAVE_NATIVE_COMP
   pdumper_set_emacs_execdir (argv0);
 #else