Add debug verbose output to show how evsels were reordered by
parse_events__sort_events_and_fix_groups. For example:
```
$ perf record -v -e '{instructions,cycles}' true
Using CPUID GenuineIntel-6-B7-1
WARNING: events were regrouped to match PMUs
evlist after sorting/fixing: '{cpu_atom/instructions/,cpu_atom/cycles/},{cpu_core/instructions/,cpu_core/cycles/}'
```

Signed-off-by: Ian Rogers <irogers@google.com>
---
 tools/perf/util/parse-events.c | 16 +++++++++++++---
 1 file changed, 13 insertions(+), 3 deletions(-)

diff --git a/tools/perf/util/parse-events.c b/tools/perf/util/parse-events.c
index 5152fd5a6ead..7952f431f82b 100644
--- a/tools/perf/util/parse-events.c
+++ b/tools/perf/util/parse-events.c
@@ -28,6 +28,7 @@
 #include "util/evsel_config.h"
 #include "util/event.h"
 #include "util/bpf-filter.h"
+#include "util/stat.h"
 #include "util/util.h"
 #include "tracepoint.h"
 
@@ -2196,14 +2197,23 @@ int __parse_events(struct evlist *evlist, const char *str, const char *pmu_filte
 	if (ret2 < 0)
 		return ret;
 
-	if (ret2 && warn_if_reordered && !parse_state.wild_card_pmus)
-		pr_warning("WARNING: events were regrouped to match PMUs\n");
-
 	/*
 	 * Add list to the evlist even with errors to allow callers to clean up.
 	 */
 	evlist__splice_list_tail(evlist, &parse_state.list);
 
+	if (ret2 && warn_if_reordered && !parse_state.wild_card_pmus) {
+		pr_warning("WARNING: events were regrouped to match PMUs\n");
+
+		if (verbose > 0) {
+			struct strbuf sb = STRBUF_INIT;
+
+			evlist__uniquify_name(evlist);
+			evlist__format_evsels(evlist, &sb, 2048);
+			pr_debug("evlist after sorting/fixing: '%s'\n", sb.buf);
+			strbuf_release(&sb);
+		}
+	}
 	if (!ret) {
 		struct evsel *last;
 
-- 
2.49.0.504.g3bcea36a83-goog