perf diff: Use internal rb tree for hists__precompute

There's missing change for hists__precompute to iterate either
entries_collapsed or entries_in tree. The change was initiated
for hists_compute_resort function in commit:

  66f97ed perf diff: Use internal rb tree for compute resort

but was missing for hists__precompute function changes.

Signed-off-by: Jiri Olsa <jolsa@redhat.com>
Cc: Corey Ashford <cjashfor@linux.vnet.ibm.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1355404152-16523-2-git-send-email-jolsa@redhat.com
[ committer note: Reduce patch size, no functional change ]
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/builtin-diff.c

@@ -323,13 +323,20 @@ static void hists__baseline_only(struct hists *hists)
 
 static void hists__precompute(struct hists *hists)
 {
-	struct rb_node *next = rb_first(&hists->entries);
+	struct rb_root *root;
+	struct rb_node *next;
+
+	if (sort__need_collapse)
+		root = &hists->entries_collapsed;
+	else
+		root = hists->entries_in;
 
+	next = rb_first(root);
 	while (next != NULL) {
-		struct hist_entry *he = rb_entry(next, struct hist_entry, rb_node);
+		struct hist_entry *he = rb_entry(next, struct hist_entry, rb_node_in);
 		struct hist_entry *pair = hist_entry__next_pair(he);
 
-		next = rb_next(&he->rb_node);
+		next = rb_next(&he->rb_node_in);
 		if (!pair)
 			continue;