[PATCH] Make RewriteBuffer write in chunks

[Alp Toker]

On 08/11/2013 20:26, Manuel Klimek wrote:
>  raw_ostream &RewriteBuffer::write(raw_ostream &os) const {
> -  // FIXME: eliminate the copy by writing out each chunk at a time
> -  os << std::string(begin(), end());
> +  for (RopePieceBTreeIterator I = begin(), E = end(); I != E;
> +       I.MoveToNextPiece())
> +    os << I.piece();
>    return os;
>
> Why's it not ok to write ++I? (if there is a good reason, a comment
> might help...)
>

The operator iterates individually through each character in the source
file, whereas MoveToNextPiece() gets us directly to the next chunk
letting us write/memcpy() directly into the output stream.

Looking through SVN history I see that the efficient accessors were
'cleaned' away as dead code and it ended up as a FIXME.

Will add a comment.

Alp.


>
>
>
> On Fri, Nov 8, 2013 at 1:41 AM, Alp Toker <alp at nuanti.com
> <mailto:alp at nuanti.com>> wrote:
>
>     Updated patch to use StringRef instead of RopePieceBTreeIterator
>     internals.
>
>     Check it out
>
>     Alp.
>
>
>     On 07/11/2013 07:08, Alp Toker wrote:
>     > Rewrite was previously allocating potentially huge std::strings with
>     > each call and filling it one character at a time.
>     >
>     > This has become a hot path for Refactoring, Modernize, FixIt,
>     Format,
>     > and particularly ARCMT/ObjCMT which call it multiple times on
>     the full
>     > source tree -- so copying out contiguous chunks while avoiding large
>     > allocations is a good idea.
>     >
>     > This commit preserves the existing interface of RewriteRope and
>     pokes
>     > into it directly for access to the byte vectors.
>     >
>     > Resolves a FIXME back from r101521. No change in behaviour.
>     >
>
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