perf parse-events: Move slots only with topdown

If slots isn't with a topdown event then moving it is unnecessary. For
example {instructions, slots} is re-ordered:

  $ perf stat -e '{instructions,slots}' -a sleep 1

   Performance counter stats for 'system wide':

         936,600,825      slots
         144,440,968      instructions

         1.006061423 seconds time elapsed

Which can break tools expecting the command line order to match the
printed order. It is necessary to move the slots event first when it
appears with topdown events. Add extra checking so that the slots event
is only moved in the case of there being a topdown event like:

  $ perf stat -e '{instructions,slots,topdown-fe-bound}' -a sleep 1

   Performance counter stats for 'system wide':

          2427568570      slots
           300927614      instructions
           551021649      topdown-fe-bound

         1.001771803 seconds time elapsed

Fixes: 94dbfd6 ("perf parse-events: Architecture specific leader override")
Reported-by: Kan Liang <kan.liang@linux.intel.com>
Signed-off-by: Ian Rogers <irogers@google.com>
Tested-by: Kan Liang <kan.liang@linux.intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Alexandre Torgue <alexandre.torgue@foss.st.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: James Clark <james.clark@arm.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: John Garry <john.garry@huawei.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Maxime Coquelin <mcoquelin.stm32@gmail.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Xing Zhengjun <zhengjun.xing@linux.intel.com>
Link: https://lore.kernel.org/r/20220321223344.1034479-1-irogers@google.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/arch/x86/util/evlist.c

@@ -20,17 +20,27 @@ int arch_evlist__add_default_attrs(struct evlist *evlist)
 
 struct evsel *arch_evlist__leader(struct list_head *list)
 {
-	struct evsel *evsel, *first;
+	struct evsel *evsel, *first, *slots = NULL;
+	bool has_topdown = false;
 
 	first = list_first_entry(list, struct evsel, core.node);
 
 	if (!pmu_have_event("cpu", "slots"))
 		return first;
 
+	/* If there is a slots event and a topdown event then the slots event comes first. */
 	__evlist__for_each_entry(list, evsel) {
-		if (evsel->pmu_name && !strcmp(evsel->pmu_name, "cpu") &&
-			evsel->name && strcasestr(evsel->name, "slots"))
-			return evsel;
+		if (evsel->pmu_name && !strcmp(evsel->pmu_name, "cpu") && evsel->name) {
+			if (strcasestr(evsel->name, "slots")) {
+				slots = evsel;
+				if (slots == first)
+					return first;
+			}
+			if (!strncasecmp(evsel->name, "topdown", 7))
+				has_topdown = true;
+			if (slots && has_topdown)
+				return slots;
+		}
 	}
 	return first;
 }