commit d918a8fb8cbca3b3ac6c73fc62b38d21f5b70386
Author: Joel Brobecker <brobecker@adacore.com>
Date:   Thu Sep 3 11:16:44 2009 -0700

        Avoid quadratic behavior when computing the value of a register.
        * frame.c (frame_cache): New static constant.
        (frame_cache_add, frame_cache_find, frame_cache_invalidate):
        New functions.
        (get_frame_id): Minor reformatting. Add the frame to the frame cache.
        (frame_find_by_id): Search the frame cache first before walking all
        frames starting from te current_frame.
        (reinit_frame_cache): Add call to frame_cache_invalidate ();

diff --git a/gdb/frame.c b/gdb/frame.c
index 67e0607..c12be5e 100644
--- a/gdb/frame.c
+++ b/gdb/frame.c
@@ -122,6 +122,37 @@ struct frame_info
   enum unwind_stop_reason stop_reason;
 };
 
+/* A Frame cache used to speed up frame lookups.  */
+
+/* We currently only cache one frame, as this seems to be sufficient
+   for now.  */
+static struct frame_info *frame_cache = NULL;
+
+/* Add the following FRAME to the frame cache.  */
+static void
+frame_cache_add (struct frame_info *frame)
+{
+  frame_cache = frame;
+}
+
+/* Search the frame cache for an entry with the given frame ID.
+   If found, return that frame.  Otherwise return NULL.  */
+static struct frame_info *
+frame_cache_find (struct frame_id id)
+{
+  if (frame_cache && frame_id_eq (frame_cache->this_id.value, id))
+    return frame_cache;
+
+  return NULL;
+}
+
+/* Invalidate the frame cache by removing all entries in the cache.  */
+static void
+frame_cache_invalidate (void)
+{
+  frame_cache = NULL;
+}
+
 /* Flag to control debugging.  */
 
 int frame_debug;
@@ -279,9 +310,8 @@ struct frame_id
 get_frame_id (struct frame_info *fi)
 {
   if (fi == NULL)
-    {
-      return null_frame_id;
-    }
+    return null_frame_id;
+
   if (!fi->this_id.p)
     {
       if (frame_debug)
@@ -300,6 +330,9 @@ get_frame_id (struct frame_info *fi)
 	  fprintf_unfiltered (gdb_stdlog, " }\n");
 	}
     }
+
+  frame_cache_add (fi);
+
   return fi->this_id.value;
 }
 
@@ -514,6 +547,11 @@ frame_find_by_id (struct frame_id id)
   if (!frame_id_p (id))
     return NULL;
 
+  /* Try using the frame cache first.  */
+  frame = frame_cache_find (id);
+  if (frame && frame_id_eq (frame->this_id.value, id))
+    return frame;
+
   for (frame = get_current_frame (); ; frame = prev_frame)
     {
       struct frame_id this = get_frame_id (frame);
@@ -1285,6 +1323,7 @@ reinit_frame_cache (void)
 
   current_frame = NULL;		/* Invalidate cache */
   select_frame (NULL);
+  frame_cache_invalidate ();
   if (frame_debug)
     fprintf_unfiltered (gdb_stdlog, "{ reinit_frame_cache () }\n");
 }