Added %FlattenString and use it to speed up a regression test.

Added %FlattenString and use it to speed up a regression test.

Flattening strings is relatively costly and by doing it after every duplication
we avoid combinatorial explosion.

Note that flattening could have been done by e.g. using a regular expression,
too, but this is just another implementation detail and %FlattenString seems
general enough to be useful in other tests, too.

Committed: http://code.google.com/p/v8/source/detail?r=13337

[Michael Starzinger, 2013-01-09 09:09:40]

LGTM (with a nit).

https://codereview.chromium.org/11828014/diff/1/src/runtime.h
File src/runtime.h (right):

https://codereview.chromium.org/11828014/diff/1/src/runtime.h#newcode377
src/runtime.h:377: F(FlattenString, 1, 1) \
Nit of the day: I think this better fits into the /* Utilities */ category
further up.

[Yang, 2013-01-09 09:12:38]

On 2013/01/09 09:09:40, Michael Starzinger wrote:
> LGTM (with a nit).
> 
> https://codereview.chromium.org/11828014/diff/1/src/runtime.h
> File src/runtime.h (right):
> 
> https://codereview.chromium.org/11828014/diff/1/src/runtime.h#newcode377
> src/runtime.h:377: F(FlattenString, 1, 1) \
> Nit of the day: I think this better fits into the /* Utilities */ category
> further up.

drive-by: test/mjsunit/substr.js uses /x/ to flatten. Replace there too? There
are probably more places like this.

[Sven Panne, 2013-01-09 09:28:42]

Regarding the use of %FlattenString in other tests: I'd like to drive the
decision where to use this performance hack by, well, performance numbers. :-)
Currently substr.js is not even in the top 20 long runner hit list...

Landing.

https://codereview.chromium.org/11828014/diff/1/src/runtime.h
File src/runtime.h (right):

https://codereview.chromium.org/11828014/diff/1/src/runtime.h#newcode377
src/runtime.h:377: F(FlattenString, 1, 1) \
On 2013/01/09 09:09:40, Michael Starzinger wrote:
> Nit of the day: I think this better fits into the /* Utilities */ category
> further up.

Done.