MIPS: Improve performance of keyed loads/stores which have a HeapNumber index.

MIPS: Improve performance of keyed loads/stores which have a HeapNumber index.

Port r11282 (bd2ab07).

Patch by Daniel Kalmar.

Original commit message:

Some GWT compiled code results in array access that has a heap number (e.g. -0)
as an index. Until now this would result in a generic IC.

For example:

a[-0] === a[0] or

a[0.25 * 4] === a[1]

This change detects heap numbers that are representable as a smi
and converts them. As a result we can still use the fast keyed monomorphic
ICs. Optimized code already handles keyed access with a double-key efficiently.

As a result the frame rate on the reported benchmark improves by roughly 2x.

BUG=
TEST=
Committed: https://code.google.com/p/v8/source/detail?r=11318

[fschneider, 2012-04-13 07:45:17]

LGTM.

Thanks for the patch. I'll land it.

[fschneider, 2012-04-13 13:05:11]

On 2012/04/13 07:45:17, fschneider wrote:
> LGTM.
> 
> Thanks for the patch. I'll land it.

Landed in r11318.