tracing: Rewrite filter logic to be simpler and faster

Al Viro reviewed the filter logic of ftrace trace events and found it to be
very troubling. It creates a binary tree based on the logic operators and
walks it during tracing. He sent myself and Tom Zanussi a long explanation
(and formal proof) of how to do the string parsing better and end up with a
program array that can be simply iterated to come up with the correct
results.

I took his ideas and his pseudo code and rewrote the filter logic based on
them. In doing so, I was able to remove a lot of code, and have a much more
condensed filter logic in the process. I wrote a very long comment
describing the methadology that Al proposed in my own words. For more info
on how this works, read the comment above predicate_parse().

Suggested-by: Al Viro <viro@ZenIV.linux.org.uk>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

kernel/trace/trace.h

@@ -1216,11 +1216,10 @@ struct ftrace_event_field {
 	int			is_signed;
 };
 
+struct prog_entry;
+
 struct event_filter {
-	int			n_preds;	/* Number assigned */
-	int			a_preds;	/* allocated */
-	struct filter_pred __rcu	*preds;
-	struct filter_pred __rcu	*root;
+	struct prog_entry __rcu	*prog;
 	char			*filter_string;
 };
 
@@ -1415,10 +1414,6 @@ struct filter_pred {
 	int 			offset;
 	int			not;
 	int 			op;
-	unsigned short		index;
-	unsigned short		parent;
-	unsigned short		left;
-	unsigned short		right;
 };
 
 static inline bool is_string_field(struct ftrace_event_field *field)