perf diff: Start moving to support matching more than two hists

We want to match more than two hists, so that we can match more than two
perf.data files and moreover, match hist_entries (buckets) in multiple
events in a group.

So the "baseline"/"leader" will instead of a ->pair pointer, use a
list_head, that will link to the pairs and hists__match use it.

Following that perf_evlist__link will link the hists in its evsel
groups.

Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Namhyung Kim <namhyung@gmail.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/n/tip-2kbmzepoi544ygj9godseqpv@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
diff --git a/tools/perf/builtin-diff.c b/tools/perf/builtin-diff.c
index 380683d..8a9db38 100644
--- a/tools/perf/builtin-diff.c
+++ b/tools/perf/builtin-diff.c
@@ -154,7 +154,7 @@
 
 double perf_diff__compute_delta(struct hist_entry *he)
 {
-	struct hist_entry *pair = he->pair;
+	struct hist_entry *pair = hist_entry__next_pair(he);
 	double new_percent = get_period_percent(he, he->stat.period);
 	double old_percent = pair ? get_period_percent(pair, pair->stat.period) : 0.0;
 
@@ -165,7 +165,7 @@
 
 double perf_diff__compute_ratio(struct hist_entry *he)
 {
-	struct hist_entry *pair = he->pair;
+	struct hist_entry *pair = hist_entry__next_pair(he);
 	double new_period = he->stat.period;
 	double old_period = pair ? pair->stat.period : 0;
 
@@ -176,7 +176,7 @@
 
 s64 perf_diff__compute_wdiff(struct hist_entry *he)
 {
-	struct hist_entry *pair = he->pair;
+	struct hist_entry *pair = hist_entry__next_pair(he);
 	u64 new_period = he->stat.period;
 	u64 old_period = pair ? pair->stat.period : 0;
 
@@ -193,7 +193,7 @@
 
 static int formula_delta(struct hist_entry *he, char *buf, size_t size)
 {
-	struct hist_entry *pair = he->pair;
+	struct hist_entry *pair = hist_entry__next_pair(he);
 
 	if (!pair)
 		return -1;
@@ -207,7 +207,7 @@
 
 static int formula_ratio(struct hist_entry *he, char *buf, size_t size)
 {
-	struct hist_entry *pair = he->pair;
+	struct hist_entry *pair = hist_entry__next_pair(he);
 	double new_period = he->stat.period;
 	double old_period = pair ? pair->stat.period : 0;
 
@@ -219,7 +219,7 @@
 
 static int formula_wdiff(struct hist_entry *he, char *buf, size_t size)
 {
-	struct hist_entry *pair = he->pair;
+	struct hist_entry *pair = hist_entry__next_pair(he);
 	u64 new_period = he->stat.period;
 	u64 old_period = pair ? pair->stat.period : 0;
 
@@ -359,8 +359,11 @@
 	struct rb_node *nd;
 
 	for (nd = rb_first(&newer->entries); nd; nd = rb_next(nd)) {
-		struct hist_entry *pos = rb_entry(nd, struct hist_entry, rb_node);
-		pos->pair = hists__find_entry(older, pos);
+		struct hist_entry *pos = rb_entry(nd, struct hist_entry, rb_node),
+				  *pair = hists__find_entry(older, pos);
+
+		if (pair)
+			hist__entry_add_pair(pos, pair);
 	}
 }
 
@@ -402,7 +405,7 @@
 		struct hist_entry *he = rb_entry(next, struct hist_entry, rb_node);
 
 		next = rb_next(&he->rb_node);
-		if (!he->pair) {
+		if (!hist_entry__next_pair(he)) {
 			rb_erase(&he->rb_node, &hists->entries);
 			hist_entry__free(he);
 		}