Introduce %_IsMinusZero.

Introduce %_IsMinusZero.

R=jkummerow@chromium.org
BUG=

Committed: https://code.google.com/p/v8/source/detail?r=17639

[Yang, 2013-11-11 14:04:50]

Please take a look.

I'll port to x64 and arm in following patch sets.

[Yang, 2013-11-12 09:29:07]

On 2013/11/11 14:04:50, Yang wrote:
> Please take a look.
> 
> I'll port to x64 and arm in following patch sets.

platform ports are also done.

[Jakob Kummerow, 2013-11-12 11:42:09]

LGTM.

For the record: as discussed, we could save some lithium-codegen code by
blacklisting Tagged representation (hence only requiring code for Double); but
for now we'll keep the current implementation for two reasons:
(1) no expected performance difference for anticipated use cases
(2) behavior difference: on non-number input, requiring Double would deopt,
which might be undesirable, whereas the current implementation would simply
branch to "false".

[Yang, 2013-11-12 11:53:28]

Committed patchset #4 manually as r17639 (presubmit successful).