Improve string runtime compare performance for flat strings.

Improve string runtime compare performance for flat strings.

Committed: http://code.google.com/p/v8/source/detail?r=3949

[Vitaly Repeshko, 2010-02-19 19:52:32]

Mads, Søren,

This speeds up Dromaeo string compare by 16%. I'm doing some extra uint32_t vs.
uintptr_t benchmarking to select the best type for x64.


Thanks,
Vitaly

[Søren Thygesen Gjesse, 2010-02-22 10:14:00]

LGTM

http://codereview.chromium.org/650058/diff/1/3
File src/runtime.cc (right):

http://codereview.chromium.org/650058/diff/1/3#newcode4639
src/runtime.cc:4639: if (x->IsFlat() && y->IsFlat()) {
How about moving the body of this if into a function, e.g. FlatStringCompare?

And make it into an if/else.

http://codereview.chromium.org/650058/diff/1/3#newcode4665
src/runtime.cc:4665: r = CompareChars(x_chars.start(), y_chars.start(),
prefix_length);
There is a wmemcmp in wchar.h - don't know if it makes sense to use it here.

[Vitaly Repeshko, 2010-02-25 12:50:10]

Thanks! Submitted.

BTW, uintptr_t turned out to be faster for large strings on x64.


-- Vitaly

http://codereview.chromium.org/650058/diff/1/3
File src/runtime.cc (right):

http://codereview.chromium.org/650058/diff/1/3#newcode4639
src/runtime.cc:4639: if (x->IsFlat() && y->IsFlat()) {
On 2010/02/22 10:14:00, Søren Gjesse wrote:
> How about moving the body of this if into a function, e.g. FlatStringCompare?
> 
> And make it into an if/else.

Done.

http://codereview.chromium.org/650058/diff/1/3#newcode4665
src/runtime.cc:4665: r = CompareChars(x_chars.start(), y_chars.start(),
prefix_length);
On 2010/02/22 10:14:00, Søren Gjesse wrote:
> There is a wmemcmp in wchar.h - don't know if it makes sense to use it here.

I'm worried about variations in wchar_t definitions.