perf parse-events: Avoid copying an empty list

In parse_events_add_pmu, delay copying the list of terms until it is
known the list contains terms.

Signed-off-by: Ian Rogers <irogers@google.com>
Reviewed-by: Kan Liang <kan.liang@linux.intel.com>
Tested-by: Atish Patra <atishp@rivosinc.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Beeman Strong <beeman@rivosinc.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: James Clark <james.clark@arm.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/r/20240416061533.921723-4-irogers@google.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/parse-events.c

@@ -1398,37 +1398,29 @@ static int parse_events_add_pmu(struct parse_events_state *parse_state,
 	struct parse_events_terms parsed_terms;
 	bool alias_rewrote_terms = false;
 
-	parse_events_terms__init(&parsed_terms);
-	if (const_parsed_terms) {
-		int ret = parse_events_terms__copy(const_parsed_terms, &parsed_terms);
-
-		if (ret)
-			return ret;
-	}
-
 	if (verbose > 1) {
 		struct strbuf sb;
 
 		strbuf_init(&sb, /*hint=*/ 0);
-		if (pmu->selectable && list_empty(&parsed_terms.terms)) {
+		if (pmu->selectable && const_parsed_terms &&
+		    list_empty(&const_parsed_terms->terms)) {
 			strbuf_addf(&sb, "%s//", pmu->name);
 		} else {
 			strbuf_addf(&sb, "%s/", pmu->name);
-			parse_events_terms__to_strbuf(&parsed_terms, &sb);
+			parse_events_terms__to_strbuf(const_parsed_terms, &sb);
 			strbuf_addch(&sb, '/');
 		}
 		fprintf(stderr, "Attempt to add: %s\n", sb.buf);
 		strbuf_release(&sb);
 	}
-	fix_raw(&parsed_terms, pmu);
 
 	memset(&attr, 0, sizeof(attr));
 	if (pmu->perf_event_attr_init_default)
 		pmu->perf_event_attr_init_default(pmu, &attr);
 
 	attr.type = pmu->type;
 
-	if (list_empty(&parsed_terms.terms)) {
+	if (!const_parsed_terms || list_empty(&const_parsed_terms->terms)) {
 		evsel = __add_event(list, &parse_state->idx, &attr,
 				    /*init_attr=*/true, /*name=*/NULL,
 				    /*metric_id=*/NULL, pmu,
@@ -1437,6 +1429,15 @@ static int parse_events_add_pmu(struct parse_events_state *parse_state,
 		return evsel ? 0 : -ENOMEM;
 	}
 
+	parse_events_terms__init(&parsed_terms);
+	if (const_parsed_terms) {
+		int ret = parse_events_terms__copy(const_parsed_terms, &parsed_terms);
+
+		if (ret)
+			return ret;
+	}
+	fix_raw(&parsed_terms, pmu);
+
 	/* Configure attr/terms with a known PMU, this will set hardcoded terms. */
 	if (config_attr(&attr, &parsed_terms, parse_state->error, config_term_pmu)) {
 		parse_events_terms__exit(&parsed_terms);