perf evlist: Remove nr_groups

Maintaining the number of groups during event parsing is problematic
and since changing to sort/regroup events can only be computed by a
linear pass over the evlist. As the value is generally only used in
tests, rather than hold it in a variable compute it by passing over
the evlist when necessary.

This change highlights that libpfm's counting of groups with a single
entry disagreed with regular event parsing. The libpfm tests are
updated accordingly.

Signed-off-by: Ian Rogers <irogers@google.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Florian Fischer <florian.fischer@muhq.space>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: James Clark <james.clark@arm.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: John Garry <john.g.garry@oracle.com>
Cc: Kajol Jain <kjain@linux.ibm.com>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Kim Phillips <kim.phillips@amd.com>
Cc: Leo Yan <leo.yan@linaro.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ravi Bangoria <ravi.bangoria@amd.com>
Cc: Sean Christopherson <seanjc@google.com>
Cc: Steinar H. Gunderson <sesse@google.com>
Cc: Stephane Eranian <eranian@google.com>
Cc: Suzuki Poulouse <suzuki.poulose@arm.com>
Cc: Xing Zhengjun <zhengjun.xing@linux.intel.com>
Link: https://lore.kernel.org/r/20230312021543.3060328-2-irogers@google.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/lib/perf/include/internal/evlist.h

@@ -17,7 +17,6 @@ struct perf_mmap_param;
 struct perf_evlist {
 	struct list_head	 entries;
 	int			 nr_entries;
-	int			 nr_groups;
 	bool			 has_user_cpus;
 	bool			 needs_map_propagation;
 	/**

tools/lib/perf/include/perf/evlist.h

@@ -47,4 +47,5 @@ LIBPERF_API struct perf_mmap *perf_evlist__next_mmap(struct perf_evlist *evlist,
 	     (pos) = perf_evlist__next_mmap((evlist), (pos), overwrite))
 
 LIBPERF_API void perf_evlist__set_leader(struct perf_evlist *evlist);
+LIBPERF_API int perf_evlist__nr_groups(struct perf_evlist *evlist);
 #endif /* __LIBPERF_EVLIST_H */