Some string optimizations:

Some string optimizations:

 * Faster hashing for sequential strings.

 * When adding short external two-byte strings try to convert them
   back to ascii. Chances are high the embedder uses two-byte
   representation even for ascii strings. This optimization saves
   memory and makes hashing faster.

Committed: http://code.google.com/p/v8/source/detail?r=4300

[antonm, 2010-03-26 18:54:35]

LGTM

http://codereview.chromium.org/1444001/diff/1/3
File src/objects-inl.h (right):

http://codereview.chromium.org/1444001/diff/1/3#newcode261
src/objects-inl.h:261: for (int i = 0, len = length(); i < len; i++) {
maybe prefetch length() not to call virtual method in the loop?

http://codereview.chromium.org/1444001/diff/1/4
File src/objects.cc (right):

http://codereview.chromium.org/1444001/diff/1/4#newcode4668
src/objects.cc:4668: for (i = 0; hasher.is_array_index() && i < length; i++) {
would you mind putting i < length into parenthesis?  I am always uneasy figuring
out priorities :)

http://codereview.chromium.org/1444001/diff/1/4#newcode4687
src/objects.cc:4687: if (StringShape(this).IsSequentialAscii()) {
what's the benefit of doing StringShape(this) several times?  Maybe only once or
use ->IsAscii... (or there are some missing checks?)

[Vitaly Repeshko, 2010-03-26 19:04:17]

Thanks!


-- Vitaly

http://codereview.chromium.org/1444001/diff/1/3
File src/objects-inl.h (right):

http://codereview.chromium.org/1444001/diff/1/3#newcode261
src/objects-inl.h:261: for (int i = 0, len = length(); i < len; i++) {
On 2010/03/26 18:54:35, antonm wrote:
> maybe prefetch length() not to call virtual method in the loop?

Huh?

http://codereview.chromium.org/1444001/diff/1/4
File src/objects.cc (right):

http://codereview.chromium.org/1444001/diff/1/4#newcode4668
src/objects.cc:4668: for (i = 0; hasher.is_array_index() && i < length; i++) {
On 2010/03/26 18:54:35, antonm wrote:
> would you mind putting i < length into parenthesis?  I am always uneasy
figuring
> out priorities :)

Done.

http://codereview.chromium.org/1444001/diff/1/4#newcode4687
src/objects.cc:4687: if (StringShape(this).IsSequentialAscii()) {
On 2010/03/26 18:54:35, antonm wrote:
> what's the benefit of doing StringShape(this) several times?  Maybe only once
or
> use ->IsAscii... (or there are some missing checks?)

There's no other function on String to test for sequential ascii/two-byte
shapes. IsSeqAsciiString and IsSeqTwoByteString are functions on Object that
also tests whether an object is a String.

[antonm, 2010-03-26 19:08:12]

Still LGTM

http://codereview.chromium.org/1444001/diff/1/3
File src/objects-inl.h (right):

http://codereview.chromium.org/1444001/diff/1/3#newcode261
src/objects-inl.h:261: for (int i = 0, len = length(); i < len; i++) {
On 2010/03/26 19:04:17, Vitaly wrote:
> On 2010/03/26 18:54:35, antonm wrote:
> > maybe prefetch length() not to call virtual method in the loop?
> 
> Huh?

Sorry, didn't notice you already do it.