Use Unique<Object> in HConstant and remove UniqueValueId.

Use Unique<Object> in HConstant and remove UniqueValueId.

BUG=
R=verwaest@chromium.org

Committed: https://code.google.com/p/v8/source/detail?r=16911

[titzer, 2013-09-24 08:58:41]

This is the last holdout with UniqueValueId.

I plan to introduce a uniqueness scope in a future CL as we discussed in person.

[Toon Verwaest, 2013-09-24 09:17:54]

lgtm with nits

https://codereview.chromium.org/24350014/diff/1/src/hydrogen-instructions.h
File src/hydrogen-instructions.h (right):

https://codereview.chromium.org/24350014/diff/1/src/hydrogen-instructions.h#n...
src/hydrogen-instructions.h:3468: // If this is a numerical constant, object_
either points to to the
points to to the -> points to the

https://codereview.chromium.org/24350014/diff/1/src/unique.h
File src/unique.h (left):

https://codereview.chromium.org/24350014/diff/1/src/unique.h#oldcode115
src/unique.h:115: // WARNING: Only do this if you have access to the heap.
Any reason you removed this comment?

[titzer, 2013-09-24 09:24:47]

On 2013/09/24 09:17:54, Toon Verwaest wrote:
> lgtm with nits
> 
> https://codereview.chromium.org/24350014/diff/1/src/hydrogen-instructions.h
> File src/hydrogen-instructions.h (right):
> 
>
https://codereview.chromium.org/24350014/diff/1/src/hydrogen-instructions.h#n...
> src/hydrogen-instructions.h:3468: // If this is a numerical constant, object_
> either points to to the
> points to to the -> points to the
> 

Done.

> https://codereview.chromium.org/24350014/diff/1/src/unique.h
> File src/unique.h (left):
> 
> https://codereview.chromium.org/24350014/diff/1/src/unique.h#oldcode115
> src/unique.h:115: // WARNING: Only do this if you have access to the heap.
> Any reason you removed this comment?

Because it turns out that we often get the handle out to pass it somewhere else,
without dereferencing it. That's safe. The unsafe part would be the dereference
of that handle (where the normal rules of handle dereferencing apply), or trying
to make another Unique in a different uniqueness scope (where the checks in the
constructor apply).

[titzer, 2013-09-24 09:48:49]

Committed patchset #1 manually as r16911 (presubmit successful).