[webkit-dev] Making empty vectors smaller; eliminate String::adopt(Vector)?

[Darin Fisher]

Worst case, if you needed to keep String::adopt(Vector), it seems like you
could
use a bit in StringImpl::m_hashAndFlags to record the fact that the buffer
requires
special "free" handling.

-Darin


On Wed, Dec 7, 2011 at 10:24 AM, Adam Barth <abarth at webkit.org> wrote:

> We originally used String::adopt(Vector) in the parser because we
> thought it would be faster, but studying profiles and experimenting
> with benchmarks revealed that (at least for those use cases) it was
> actually slower than just memcpying the data into the String.  I
> haven't looked at the other uses of String::adopt(Vector) in the
> codebase, but they might also run faster using memcpy.
>
> I think it's probably fine to remove String::adopt(Vector).
>
> Adam
>
>
> On Wed, Dec 7, 2011 at 10:10 AM, Darin Adler <darin at apple.com> wrote:
> > For vectors with no inline capacity, we can store the capacity inside
> the Vector’s buffer. That way, the Vector itself will be one size_t smaller
> when empty. In fact, with a bit of performance risk, we can do the same
> thing with the vector’s size, making an empty Vector just a single pointer.
> But doing this also means that the allocated buffer won’t have the vector
> elements at the start of the memory block. The only thing I could find that
> this would interfere with would be the String::adopt(Vector) function. My
> question is whether with the latest wonderful StringBuilder technology we
> could eliminate String::adopt(Vector). Can we get rid of that entirely from
> WebKit?
> >
> > -- Darin
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