Avoid bailing out to runtime for short substrings.

test/mjsunit/string-slices.js

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 142 matching lines @@
 for ( var i = 0; i < 1000; i++) {
   f(flat, cons, slice, i);
 }
 flat = "abcdefghijkl1\u20232345";
 cons = flat + flat.toUpperCase();
 slice = "abcdefghijklmn1\u20232345".slice(1, -1);
 for ( var i = 0; i < 1000; i++) {
   f(flat, cons, slice, i);
 }
 
+// Short substrings.
+flat = "abcdefghijkl12345";
+cons = flat + flat.toUpperCase();
+/x/.exec(cons);  // Flatten cons
+slice = "abcdefghijklmn12345".slice(1, -1);
+assertEquals("cdefg", flat.substr(2, 5));
+assertEquals("cdefg", cons.substr(2, 5));
+assertEquals("cdefg", slice.substr(1, 5));
+
+flat = "abc\u1234defghijkl12345";
+cons = flat + flat.toUpperCase();
+/x/.exec(cons);  // Flatten cons
+slice = "abc\u1234defghijklmn12345".slice(1, -1);
+assertEquals("c\u1234def", flat.substr(2, 5));
+assertEquals("c\u1234def", cons.substr(2, 5));
+assertEquals("c\u1234def", slice.substr(1, 5));
+
 // Concatenate substrings.
 var ascii = 'abcdefghijklmnop';
 var utf = '\u03B1\u03B2\u03B3\u03B4\u03B5\u03B6\u03B7\u03B8\u03B9\u03BA\u03BB';
 assertEquals("klmno", ascii.substring(10,15) + ascii.substring(16));
 assertEquals("\u03B4\u03B7", utf.substring(3,4) + utf.substring(6,7));
 assertEquals("klp", ascii.substring(10,12) + ascii.substring(15,16));
 assertEquals("\u03B1\u03B4\u03B5", utf.substring(0,1) + utf.substring(5,3));
 assertEquals("", ascii.substring(16) + utf.substring(16));
 assertEquals("bcdef\u03B4\u03B5\u03B6\u03B7\u03B8\u03B9",
     ascii.substring(1,6) + utf.substring(3,9));
@@ skipping 26 matching lines @@
     assertEquals(b.charAt(4), c.charAt(4));
     assertTrue(/3456789qwe/.test(c));
     assertEquals(4, c.indexOf("678"));
     assertEquals("2345", c.split("6")[0]);
   }
 }
 
 test_crankshaft();
 %OptimizeFunctionOnNextCall(test_crankshaft);
 test_crankshaft();