Tweak builtin symbol order for speed

* lib-src/make-docfile.c (compare_globals):
Make symbols 1 through 4 be t, unbound, error, lambda.
This is in addition to symbol 0 being nil.
This change improved ‘make compile-always’ performance by 0.6%
on my platform.

1 files changed, 16 insertions, 5 deletions

diff --git a/lib-src/make-docfile.c b/lib-src/make-docfile.c
index 4d25b0a6b93..368150be067 100644
--- a/lib-src/make-docfile.c
+++ b/lib-src/make-docfile.c
@@ -641,13 +641,24 @@ compare_globals (const void *a, const void *b)
     return ga->type - gb->type;
 
   /* Consider "nil" to be the least, so that iQnil is zero.  That
-     way, Qnil's internal representation is zero, which is a bit faster.  */
+     way, Qnil's internal representation is zero, which is a bit faster.
+     Similarly, consideer "t" to be the second-least, and so forth.  */
   if (ga->type == SYMBOL)
     {
-      bool a_nil = strcmp (ga->name, "Qnil") == 0;
-      bool b_nil = strcmp (gb->name, "Qnil") == 0;
-      if (a_nil | b_nil)
-        return b_nil - a_nil;
+      /* Common symbols in decreasing popularity order.  */
+      static char const commonsym[][8]
+        = { "nil", "t", "unbound", "error", "lambda" };
+      int ncommonsym = sizeof commonsym / sizeof *commonsym;
+      int ai = ncommonsym, bi = ncommonsym;
+      for (int i = 0; i < ncommonsym; i++)
+        {
+          if (ga->name[0] == 'Q' && strcmp (ga->name + 1, commonsym[i]) == 0)
+            ai = i;
+          if (gb->name[0] == 'Q' && strcmp (gb->name + 1, commonsym[i]) == 0)
+            bi = i;
+        }
+      if (! (ai == ncommonsym && bi == ncommonsym))
+        return ai - bi;
     }
 
   return strcmp (ga->name, gb->name);