diff --git a/collects/tests/mzscheme/benchmarks/rx/auto.ss b/collects/tests/mzscheme/benchmarks/rx/auto.ss
new file mode 100644
index 0000000000..745b8ae433
--- /dev/null
+++ b/collects/tests/mzscheme/benchmarks/rx/auto.ss
@@ -0,0 +1,86 @@
+
+(module mz mzscheme
+  (define (test input rx iterations)
+    (printf "Testing ~s on ~a iterations of a ~a-byte input\n" rx
+	    iterations
+	    (bytes-length input))
+    (time
+     (let loop ([n iterations])
+       (unless (zero? n)
+	 (regexp-match-positions rx input)
+	 (loop (sub1 n))))))
+
+  (define (random-letters n)
+    (let loop ([n n][accum null])
+      (if (zero? n)
+	  (list->bytes accum)
+	  (loop (sub1 n) (cons (+ (char->integer #\a)
+				  (random 26))
+			       accum)))))
+
+  (test (make-bytes 100 (char->integer #\x))  #px#"(?s:.*)" 100000)
+  (test (make-bytes 1000 (char->integer #\x))  #px#"(?s:.*)" 100000)
+  (test (make-bytes 10000 (char->integer #\x))  #px#"(?s:.*)" 10000)
+  (test (make-bytes 100000 (char->integer #\x))  #px#"(?s:.*)" 1000)
+  (test (make-bytes 100 (char->integer #\x))  #px#".*" 100000)
+  (test (make-bytes 1000 (char->integer #\x))  #px#".*" 100000)
+  (test (make-bytes 10000 (char->integer #\x))  #px#".*" 100000)
+  (test (make-bytes 100000 (char->integer #\x))  #px#".*" 10000)
+  (test (make-bytes 100 (char->integer #\x))  #px#"(?s:(.)*)" 100000)
+  (test (make-bytes 1000 (char->integer #\x))  #px#"(?s:(.)*)" 100000)
+  (test (make-bytes 10000 (char->integer #\x))  #px#"(?s:(.)*)" 10000)
+  (test (make-bytes 100000 (char->integer #\x))  #px#"(?s:(.)*)" 1000)
+  (test (make-bytes 100 (char->integer #\x))  #px#"x*" 100000)
+  (test (make-bytes 1000 (char->integer #\x))  #px#"x*" 100000)
+  (test (make-bytes 10000 (char->integer #\x))  #px#"x*" 10000)
+  (test (make-bytes 100000 (char->integer #\x))  #px#"x*" 1000)
+  (test (make-bytes 100 (char->integer #\x))  #px#"[xy]*" 100000)
+  (test (make-bytes 1000 (char->integer #\x))  #px#"[xy]*" 10000)
+  (test (make-bytes 10000 (char->integer #\x))  #px#"[xy]*" 1000)
+  (test (make-bytes 100000 (char->integer #\x))  #px#"[xy]*" 100)
+  (test (make-bytes 100 (char->integer #\x))  #px#"(.)*" 100000)
+  (test (make-bytes 1000 (char->integer #\x))  #px#"(.)*" 100000)
+  (test (make-bytes 10000 (char->integer #\x))  #px#"(.)*" 100000)
+  (test (make-bytes 100000 (char->integer #\x))  #px#"(.)*" 10000)
+  (test (make-bytes 100 (char->integer #\x))  #px#"(x)*" 100000)
+  (test (make-bytes 1000 (char->integer #\x))  #px#"(x)*" 100000)
+  (test (make-bytes 10000 (char->integer #\x))  #px#"(x)*" 10000)
+  (test (make-bytes 100000 (char->integer #\x))  #px#"(x)*" 1000)
+  (test (make-bytes 100 (char->integer #\x))  #px#"(y|x)*" 10000)
+  (test (make-bytes 1000 (char->integer #\x))  #px#"(y|x)*" 1000)
+  (test (make-bytes 10000 (char->integer #\x))  #px#"(y|x)*" 100)
+  (test (make-bytes 100000 (char->integer #\x))  #px#"(y|x)*" 10)
+  (test (make-bytes 100 (char->integer #\x))  #px#"([yz]|x)*" 10000)
+  (test (make-bytes 1000 (char->integer #\x))  #px#"([yz]|x)*" 1000)
+  (test (make-bytes 10000 (char->integer #\x))  #px#"([yz]|x)*" 100)
+  (test (make-bytes 100000 (char->integer #\x))  #px#"([yz]|x)*" 10)
+  (test (make-bytes 100 (char->integer #\x))  #px#"([xy])*" 100000)
+  (test (make-bytes 1000 (char->integer #\x))  #px#"([xy])*" 10000)
+  (test (make-bytes 10000 (char->integer #\x))  #px#"([xy])*" 1000)
+  (test (make-bytes 100000 (char->integer #\x))  #px#"([xy])*" 100)
+;  (test (make-bytes 100 (char->integer #\x))  #px#"((x){2})*" 10000)
+;  (test (make-bytes 1000 (char->integer #\x))  #px#"((x){2})*" 10000)
+;  (test (make-bytes 10000 (char->integer #\x))  #px#"((x){2})*" 1000)
+;  (test (make-bytes 100000 (char->integer #\x))  #px#"((x){2})*" 100000)
+  (test (bytes-append (random-letters 100) #"FOOBARBAZ")  #px#"[a-z]*FOOBARBAZ" 100000)
+  (test (bytes-append (random-letters 1000) #"FOOBARBAZ")  #px#"[a-z]*FOOBARBAZ" 10000)
+  (test (bytes-append (random-letters 10000) #"FOOBARBAZ")  #px#"[a-z]*FOOBARBAZ" 1000)
+  (test (bytes-append (random-letters 100) #"NOPE")  #px#"[a-z]*FOOBARBAZ" 1000000)
+  (test (bytes-append (random-letters 1000) #"NOPE")  #px#"[a-z]*FOOBARBAZ" 100000)
+  (test (bytes-append (random-letters 10000) #"NOPE")  #px#"[a-z]*FOOBARBAZ" 10000)
+  (test (bytes-append (random-letters 100) #"FOOBARBAZ")  #px#"([a-z])*FOOBARBAZ" 100000)
+  (test (bytes-append (random-letters 1000) #"FOOBARBAZ")  #px#"([a-z])*FOOBARBAZ" 10000)
+  (test (bytes-append (random-letters 10000) #"FOOBARBAZ")  #px#"([a-z])*FOOBARBAZ" 1000)
+  (test (bytes-append (random-letters 100) #"NOPE")  #px#"([a-z])*FOOBARBAZ" 1000000)
+  (test (bytes-append (random-letters 1000) #"NOPE")  #px#"([a-z])*FOOBARBAZ" 100000)
+  (test (bytes-append (random-letters 10000) #"NOPE")  #px#"([a-z])*FOOBARBAZ" 10000)
+  (test (bytes-append (random-letters 100) #"FOOBARBAZ")  #px#"([a-z]|ab)*FOOBARBAZ" 10000)
+  (test (bytes-append (random-letters 1000) #"FOOBARBAZ")  #px#"([a-z]|ab)*FOOBARBAZ" 1000)
+  (test (bytes-append (random-letters 10000) #"FOOBARBAZ")  #px#"([a-z]|ab)*FOOBARBAZ" 10)
+  (test (bytes-append (random-letters 100) #"NOPE")  #px#"([a-z]|ab)*FOOBARBAZ" 1000000)
+  (test (bytes-append (random-letters 1000) #"NOPE")  #px#"([a-z]|ab)*FOOBARBAZ" 100000)
+  (test (bytes-append (random-letters 10000) #"NOPE")  #px#"([a-z]|ab)*FOOBARBAZ" 10000)
+  (test (bytes-append (random-letters 100) #"NOPE")  #px#"(?i:[a-z]*FOOBARBAZ)" 1000)
+  (test (bytes-append (random-letters 1000) #"NOPE")  #px#"(?i:[a-z]*FOOBARBAZ)" 10)
+  (test (bytes-append (random-letters 10000) #"NOPE")  #px#"(?i:[a-z]*FOOBARBAZ)" 10)
+  )
\ No newline at end of file
diff --git a/collects/tests/mzscheme/benchmarks/rx/perl_prefix.pl b/collects/tests/mzscheme/benchmarks/rx/perl_prefix.pl
new file mode 100644
index 0000000000..60adc2e701
--- /dev/null
+++ b/collects/tests/mzscheme/benchmarks/rx/perl_prefix.pl
@@ -0,0 +1,83 @@
+
+use Time::HiRes qw(time);
+
+sub test ($$$$) {
+  local ($x, $pattern, $pstr, $times) = @_;
+
+  print "$pstr $times iterations on " . length($x) . " bytes:\n";
+
+  $start = time;
+  for ($i = 0; $i < $times; $i++) {
+    $x =~ ${pattern};
+  }
+  print (time - $start);
+    print "\n";
+}
+
+test "@{['x' x 100]}",  /(.)*/s, "/(.)*/s", 100000;
+test "@{['x' x 1000]}",  /(.)*/s, "/(.)*/s",100000;
+test "@{['x' x 10000]}",  /(.)*/s, "/(.)*/s",100000;
+test "@{['x' x 100000]}",  /(.)*/s, "/(.)*/s",10000;
+test "@{['x' x 100]}",  /.*/m, "/.*/m", 100000;
+test "@{['x' x 1000]}",  /.*/m, "/.*/m", 100000;
+test "@{['x' x 10000]}",  /.*/m, "/.*/m", 10000;
+test "@{['x' x 100000]}",  /.*/m, "/.*/m", 1000;
+test "@{['x' x 100]}",  /.*/s, "/.*/s",100000;
+test "@{['x' x 1000]}",  /.*/s, "/.*/s",100000;
+test "@{['x' x 10000]}",  /.*/s, "/.*/s",100000;
+test "@{['x' x 100000]}",  /.*/s, "/.*/s",10000;
+test "@{['x' x 100]}",  /x*/, "/x*/", 100000;
+test "@{['x' x 1000]}",  /x*/, "/x*/", 100000;
+test "@{['x' x 10000]}",  /x*/, "/x*/", 10000;
+test "@{['x' x 100000]}",  /x*/, "/x*/", 1000;
+test "@{['x' x 100]}",  /[xy]*/, "/[xy]*/", 100000;
+test "@{['x' x 1000]}",  /[xy]*/, "/[xy]*/", 10000;
+test "@{['x' x 10000]}",  /[xy]*/, "/[xy]*/", 1000;
+test "@{['x' x 100000]}",  /[xy]*/, "/[xy]*/", 100;
+test "@{['x' x 100]}",  /(.)*/m, "/(.)*/", 100000;
+test "@{['x' x 1000]}",  /(.)*/m, "/(.)*/", 100000;
+test "@{['x' x 10000]}",  /(.)*/m, "/(.)*/", 10000;
+test "@{['x' x 100000]}",  /(.)*/m, "/(.)*/", 1000;
+test "@{['x' x 100]}",  /(x)*/, "/(x)*/", 100000;
+test "@{['x' x 1000]}",  /(x)*/, "/(x)*/", 100000;
+test "@{['x' x 10000]}",  /(x)*/, "/(x)*/", 10000;
+test "@{['x' x 100000]}",  /(x)*/, "/(x)*/", 1000;
+test "@{['x' x 100]}",  /(y|x)*/, "/(y|x)*/", 10000;
+test "@{['x' x 1000]}",  /(y|x)*/, "/(y|x)*/", 1000;
+test "@{['x' x 10000]}",  /(y|x)*/, "/(y|x)*/", 100;
+test "@{['x' x 100000]}",  /(y|x)*/, "/(y|x)*/", 10;
+test "@{['x' x 100]}",  /([yz]|x)*/, "/([yz]|x)*/", 10000;
+test "@{['x' x 1000]}",  /([yz]|x)*/, "/([yz]|x)*/", 1000;
+test "@{['x' x 10000]}",  /([yz]|x)*/, "/([yz]|x)*/", 100;
+test "@{['x' x 100000]}",  /([yz]|x)*/, "/([yz]|x)*/", 10;
+test "@{['x' x 100]}",  /([xy])*/, "/([xy])*/", 100000;
+test "@{['x' x 1000]}",  /([xy])*/, "/([xy])*/", 10000;
+test "@{['x' x 10000]}",  /([xy])*/, "/([xy])*/", 1000;
+test "@{['x' x 100000]}",  /([xy])*/, "/([xy])*/", 100;
+#test "@{['x' x 100]}",  /((x){2})*/, "/((x){2})*/", 10000;
+#test "@{['x' x 1000]}",  /((x){2})*/, "/((x){2})*/", 10000;
+#test "@{['x' x 10000]}",  /((x){2})*/, "/((x){2})*/", 1000;
+#test "@{['x' x 100000]}",  /((x){2})*/, "/((x){2})*/", 100000;
+test "@{[join undef, map { chr(ord('a') + rand 26) } (1..100)]}FOOBARBAZ",  /[a-z]*FOOBARBAZ/, "/[a-z]*FOOBARBAZ/", 100000;
+test "@{[join undef, map { chr(ord('a') + rand 26) } (1..1000)]}FOOBARBAZ",  /[a-z]*FOOBARBAZ/, "/[a-z]*FOOBARBAZ/", 10000;
+test "@{[join undef, map { chr(ord('a') + rand 26) } (1..10000)]}FOOBARBAZ",  /[a-z]*FOOBARBAZ/, "/[a-z]*FOOBARBAZ/", 1000;
+test "@{[join undef, map { chr(ord('a') + rand 26) } (1..100)]}NOPE",  /[a-z]*FOOBARBAZ/, "/[a-z]*FOOBARBAZ/", 1000000;
+test "@{[join undef, map { chr(ord('a') + rand 26) } (1..1000)]}NOPE",  /[a-z]*FOOBARBAZ/, "/[a-z]*FOOBARBAZ/", 100000;
+test "@{[join undef, map { chr(ord('a') + rand 26) } (1..10000)]}NOPE",  /[a-z]*FOOBARBAZ/, "/[a-z]*FOOBARBAZ/", 10000;
+test "@{[join undef, map { chr(ord('a') + rand 26) } (1..100)]}FOOBARBAZ",  /([a-z])*FOOBARBAZ/, "/([a-z])*FOOBARBAZ/", 100000;
+test "@{[join undef, map { chr(ord('a') + rand 26) } (1..1000)]}FOOBARBAZ",  /([a-z])*FOOBARBAZ/, "/([a-z])*FOOBARBAZ/", 10000;
+test "@{[join undef, map { chr(ord('a') + rand 26) } (1..10000)]}FOOBARBAZ",  /([a-z])*FOOBARBAZ/, "/([a-z])*FOOBARBAZ/", 1000;
+test "@{[join undef, map { chr(ord('a') + rand 26) } (1..100)]}NOPE",  /([a-z])*FOOBARBAZ/, "/([a-z])*FOOBARBAZ/", 1000000;
+test "@{[join undef, map { chr(ord('a') + rand 26) } (1..1000)]}NOPE",  /([a-z])*FOOBARBAZ/, "/([a-z])*FOOBARBAZ/", 100000;
+test "@{[join undef, map { chr(ord('a') + rand 26) } (1..10000)]}NOPE",  /([a-z])*FOOBARBAZ/, "/([a-z])*FOOBARBAZ/", 10000;
+test "@{[join undef, map { chr(ord('a') + rand 26) } (1..100)]}FOOBARBAZ",  /([a-z]|ab)*FOOBARBAZ/, "/([a-z]|ab)*FOOBARBAZ/", 10000;
+test "@{[join undef, map { chr(ord('a') + rand 26) } (1..1000)]}FOOBARBAZ",  /([a-z]|ab)*FOOBARBAZ/, "/([a-z]|ab)*FOOBARBAZ/", 1000;
+test "@{[join undef, map { chr(ord('a') + rand 26) } (1..10000)]}FOOBARBAZ",  /([a-z]|ab)*FOOBARBAZ/, "/([a-z]|ab)*FOOBARBAZ/", 10;
+test "@{[join undef, map { chr(ord('a') + rand 26) } (1..100)]}NOPE",  /([a-z]|ab)*FOOBARBAZ/, "/([a-z]|ab)*FOOBARBAZ/", 1000000;
+test "@{[join undef, map { chr(ord('a') + rand 26) } (1..1000)]}NOPE",  /([a-z]|ab)*FOOBARBAZ/, "/([a-z]|ab)*FOOBARBAZ/", 100000;
+test "@{[join undef, map { chr(ord('a') + rand 26) } (1..10000)]}NOPE",  /([a-z]|ab)*FOOBARBAZ/, "/([a-z]|ab)*FOOBARBAZ/", 10000;
+test "@{[join undef, map { chr(ord('a') + rand 26) } (1..100)]}NOPE",  /[a-z]*FOOBARBAZ/i, "/[a-z]*FOOBARBAZ/i", 1000;
+test "@{[join undef, map { chr(ord('a') + rand 26) } (1..1000)]}NOPE",  /[a-z]*FOOBARBAZ/i, "/[a-z]*FOOBARBAZ/i", 10;
+test "@{[join undef, map { chr(ord('a') + rand 26) } (1..10000)]}NOPE",  /[a-z]*FOOBARBAZ/i, "/[a-z]*FOOBARBAZ/i", 10;
+
+