Some interesting cases:

use warnings;
use strict;

while (<DATA>) {
    s/(
                (?:(?:[^\/][^\/]*?|)*?  # anything, except comment sym
+bol
                ("|').*?\2              # quoted string (and take ever
+ything)
                (?:[^\/][^\/]*?|)*?     # anything, except comment sym
+bol
              )*?
            )
            (?:
              \/\/                      # comment symbol
              [^\\]*                    # anything, except continuatio
+n
            )??$
          /$1/x;

    print;
}

__DATA__
/* //
*/
/*
*/
*str = "//\"//";
[download]

Prints:

/* */
/*
*/
*str = "//\"
[download]