perf expr: Allow NaN to be a valid number

Currently only floating point numbers can be parsed, add a special
case for NaN.

Signed-off-by: Ian Rogers <[e-mail]>
Reviewed-by: Kan Liang <[e-mail]>
Cc: K Prateek Nayak <[e-mail]>
Cc: James Clark <[e-mail]>
Cc: Kaige Ye <[e-mail]>
Cc: John Garry <[e-mail]>
Signed-off-by: Namhyung Kim <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]

tools/perf/util/expr.l

···
 	}
 	return LITERAL;
 }
+
+static int nan_value(yyscan_t scanner)
+{
+	YYSTYPE *yylval = expr_get_lval(scanner);
+
+	yylval->num = NAN;
+	return NUMBER;
+}
 %}
 
 number		([0-9]+\.?[0-9]*|[0-9]*\.?[0-9]+)(e-?[0-9]+)?
···
 source_count	{ return SOURCE_COUNT; }
 has_event	{ return HAS_EVENT; }
 strcmp_cpuid_str	{ return STRCMP_CPUID_STR; }
+NaN		{ return nan_value(yyscanner); }
 {literal}	{ return literal(yyscanner, sctx); }
 {number}	{ return value(yyscanner); }
 {symbol}	{ return str(yyscanner, ID, sctx->runtime); }