tools lib traceevent: Add handler for __builtin_expect()

In order to move pointer checks like IS_ERR_VALUE() out of the hotpath
and into the reader path of a trace event, user space tools need to be
able to parse that. IS_ERR_VALUE() is defined as:

 #define IS_ERR_VALUE() unlikely((unsigned long)(void *)(x) >= (unsigned long)-MAX_ERRNO)

Which eventually turns into:

  __builtin_expect(!!((unsigned long)(void *)(x) >= (unsigned long)-4095), 0)

Now the traceevent parser can handle most of that except for the
__builtin_expect(), which needs to be added.

Link: https://lore.kernel.org/linux-mm/20200320055823.27089-3-jaewon31.kim@samsung.com/Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Jaewon Kim <jaewon31.kim@samsung.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Kees Kook <keescook@chromium.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: linux-mm@kvack.org
Cc: linux-trace-devel@vger.kernel.org
Link: http://lore.kernel.org/lkml/20200324200956.821799393@goodmis.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/lib/traceevent/event-parse.c

@@ -3084,6 +3084,37 @@ process_func_handler(struct tep_event *event, struct tep_function_handler *func,
 	return TEP_EVENT_ERROR;
 }
 
+static enum tep_event_type
+process_builtin_expect(struct tep_event *event, struct tep_print_arg *arg, char **tok)
+{
+	enum tep_event_type type;
+	char *token = NULL;
+
+	/* Handle __builtin_expect( cond, #) */
+	type = process_arg(event, arg, &token);
+
+	if (type != TEP_EVENT_DELIM || token[0] != ',')
+		goto out_free;
+
+	free_token(token);
+
+	/* We don't care what the second parameter is of the __builtin_expect() */
+	if (read_expect_type(TEP_EVENT_ITEM, &token) < 0)
+		goto out_free;
+
+	if (read_expected(TEP_EVENT_DELIM, ")") < 0)
+		goto out_free;
+
+	free_token(token);
+	type = read_token_item(tok);
+	return type;
+
+out_free:
+	free_token(token);
+	*tok = NULL;
+	return TEP_EVENT_ERROR;
+}
+
 static enum tep_event_type
 process_function(struct tep_event *event, struct tep_print_arg *arg,
 		 char *token, char **tok)
@@ -3128,6 +3159,10 @@ process_function(struct tep_event *event, struct tep_print_arg *arg,
 		free_token(token);
 		return process_dynamic_array_len(event, arg, tok);
 	}
+	if (strcmp(token, "__builtin_expect") == 0) {
+		free_token(token);
+		return process_builtin_expect(event, arg, tok);
+	}
 
 	func = find_func_handler(event->tep, token);
 	if (func) {