exceptions: avoid consing dyn env for package vars

* unwind.c (invoke_handler): Do not unconditionally bind
*package* and *package-alist*. Allocate the new dynamic
environment only if the current values of those variables are
different from the ones stored in the frame. This is the
excpected case since package and package list manipulations
are rare.

1 files changed, 7 insertions, 4 deletions

diff --git a/unwind.c b/unwind.c
index 787dcd62..ac0f2d9f 100644
--- a/unwind.c
+++ b/unwind.c
@@ -637,15 +637,18 @@ val uw_exception_subtype_p(val sub, val sup)
 static void invoke_handler(uw_frame_t *fr, struct args *args)
 {
   val saved_dyn_env = dyn_env;
+  val cur_pkg_alist = deref(cur_package_alist_loc);
+  val cur_pkg = cur_package;
 
   fr->ha.visible = 0;
 
   uw_simple_catch_begin;
 
-  dyn_env = make_env(nil, nil, dyn_env);
-
-  env_vbind(dyn_env, package_s, fr->ha.package);
-  env_vbind(dyn_env, package_alist_s, fr->ha.package_alist);
+  if (cur_pkg_alist != fr->ha.package_alist || cur_pkg != fr->ha.package) {
+    dyn_env = make_env(nil, nil, dyn_env);
+    env_vbind(dyn_env, package_s, fr->ha.package);
+    env_vbind(dyn_env, package_alist_s, fr->ha.package_alist);
+  }
 
   generic_funcall(fr->ha.fun, args);