checkpatch: reduce runtime/cpu time used

There are some cases where checkpatch can take a long time to complete.
Reduce the likelihood of this long run-time by adding a new test for lines
with and without comments and eliminating checks on lines with only
comments.

This reduces the number of "ctx_statement_block" calls, and also the
number of tests of $stat, which is now undefined for these blank lines.

One test in particular, the "check for switch/default statements without a
break", could take an extremely long time to parse as it tries to skip
interleaving comments within the ctx_statement_block/$stat and that could
be done multiple times unnecessarily.

A small test case taken from cfg80211.h before this patch would take
1000's of seconds to run, now it's just a couple seconds.
Signed-off-by: Joe Perches <joe@perches.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

scripts/checkpatch.pl

@@ -1678,6 +1678,8 @@ sub process {
 	$linenr = 0;
 	foreach my $line (@lines) {
 		$linenr++;
+		my $sline = $line;	#copy of $line
+		$sline =~ s/$;/ /g;	#with comments as spaces
 
 		my $rawline = $rawlines[$linenr - 1];
 
@@ -2194,7 +2196,7 @@ sub process {
 		    $realline_next);
 #print "LINE<$line>\n";
 		if ($linenr >= $suppress_statement &&
-		    $realcnt && $line =~ /.\s*\S/) {
+		    $realcnt && $sline =~ /.\s*\S/) {
 			($stat, $cond, $line_nr_next, $remain_next, $off_next) =
 				ctx_statement_block($linenr, $realcnt, 0);
 			$stat =~ s/\n./\n /g;