Replace ToAsciiVector and ToUC16Vector with single function that returns a tagged value.

Replace ToAsciiVector and ToUC16Vector with single function that returns a tagged value.

The tag tells whether the content is ASCII or UC16, or even if the string wasn't flat.

BUG: v8:1633

Committed: http://code.google.com/p/v8/source/detail?r=8999

[Vitaly Repeshko, 2011-08-23 10:28:28]

LGTM

http://codereview.chromium.org/7709024/diff/1/src/objects.h
File src/objects.h (right):

http://codereview.chromium.org/7709024/diff/1/src/objects.h#newcode5901
src/objects.h:5901: FlatContent GetFlatContent();
This needs some documentation.

A couple of optional ideas:
1. Take a pointer/reference to AssertNoAllocation as a parameter (similar to
write barrier) to enforce valid usage.
2. Make this->IsFlat() a requirement, since this function doesn't flatten and
the caller has to check whether the content is flat anyways.

[Yang, 2011-08-23 11:05:10]

On 2011/08/23 09:39:59, Lasse Reichstein wrote:

LGTM.

[Lasse Reichstein, 2011-08-23 12:01:55]

Added the requirement of having an AssertNoAllocation present.
Also fixed a bug that was obvious when trying to add an AssertNoAllocation. The
original version was also bugged, but less so (didn't handle a string changing
encoding during GC, would fail if not all ASCII chars are in
single-element-string-cache)

Please take a look again.

http://codereview.chromium.org/7709024/diff/1/src/objects.h
File src/objects.h (right):

http://codereview.chromium.org/7709024/diff/1/src/objects.h#newcode5901
src/objects.h:5901: FlatContent GetFlatContent();
On 2011/08/23 10:28:28, Vitaly Repeshko wrote:
> This needs some documentation.

Absolutely.

> A couple of optional ideas:
> 1. Take a pointer/reference to AssertNoAllocation as a parameter (similar to
> write barrier) to enforce valid usage.

I considered that, but decided against it. It really doesn't enforce valid
usage, since the extracted vector can survive the FlatContent. I'll have a look
at it again, because it is a good idea and it at least encourages good behavior.

> 2. Make this->IsFlat() a requirement, since this function doesn't flatten and
> the caller has to check whether the content is flat anyways.

That would require two inspections of the ConsString if it is flat - on in the
caller to see that it's flat, and one see that it's a Cons and traverse it in
GetFlatContent. This way we only check it once. I think it makes the call-points
clearer.