Avoid decoding overhead when allocating ascii strings....

Avoid decoding overhead when allocating ascii strings.

The assumption is that most utf8 strings allocated are actually ascii
and that if they are not we will encounter a non-ascii char pretty
quickly.


Committed: http://code.google.com/p/v8/source/detail?r=6099

[Lasse Reichstein, 2010-12-21 12:48:12]

Good fix.
LGTM.

http://codereview.chromium.org/6072004/diff/1/src/heap-inl.h
File src/heap-inl.h (right):

http://codereview.chromium.org/6072004/diff/1/src/heap-inl.h#newcode45
src/heap-inl.h:45: // Check for ascii first since this is the common case.
ASCII is an acronym, even though we might not respect that in function names.
More instances below.

http://codereview.chromium.org/6072004/diff/1/src/heap-inl.h#newcode47
src/heap-inl.h:47: if (static_cast<uc16>(str[i]) > String::kMaxAsciiCharCode) {
Just cast to uint8_t, and compare to String:kMaxAsciiCharCodeU. It will allow
the compiler to just check the sign bit.

[Mads Ager (chromium), 2010-12-21 12:55:52]

Thanks!

http://codereview.chromium.org/6072004/diff/1/src/heap-inl.h
File src/heap-inl.h (right):

http://codereview.chromium.org/6072004/diff/1/src/heap-inl.h#newcode45
src/heap-inl.h:45: // Check for ascii first since this is the common case.
On 2010/12/21 12:48:12, Lasse Reichstein wrote:
> ASCII is an acronym, even though we might not respect that in function names.
> More instances below.

Done.

http://codereview.chromium.org/6072004/diff/1/src/heap-inl.h#newcode47
src/heap-inl.h:47: if (static_cast<uc16>(str[i]) > String::kMaxAsciiCharCode) {
On 2010/12/21 12:48:12, Lasse Reichstein wrote:
> Just cast to uint8_t, and compare to String:kMaxAsciiCharCodeU. It will allow
> the compiler to just check the sign bit.

Done.