Optimize identical based on types.

Optimize identical based on types.

R=asgerf@google.com

Committed: https://github.com/dart-lang/sdk/commit/add53e33e773a0e1445a32b4b4289519ce745abf

[asgerf, 2015-04-20 14:23:17]

How expensive is TypeMask.intersection?

It looks like an optimization that rarely clicks in practice, so it seems
unlikely to be worth it unless the check is cheap.

[asgerf, 2015-05-19 15:15:07]

In the interest of getting this resolved I ran some benchmarks and could not
measure any difference in compile time, so LGTM.

[karlklose, 2015-05-20 09:15:25]

On 2015/05/19 15:15:07, asgerf wrote:
> In the interest of getting this resolved I ran some benchmarks and could not
> measure any difference in compile time, so LGTM.

Oh sorry, I forgot this CL. Thank you for measuring it.

In this special case, the one side should always be a base type mask, so it is
expected to be quite fast. I assume we'll need similar tests for type based
optimizations in the future, so if the operations on TypeMasks are not fast
enough, we may want to have more specialized approximating tests.

[karlklose, 2015-06-01 12:38:59]

Rebased and added missing check for nullability.

[asgerf, 2015-06-01 12:39:59]

On 2015/06/01 12:38:59, karlklose wrote:
> Rebased and added missing check for nullability.

No patch was uploaded.

[karlklose, 2015-06-02 11:01:48]

Committed patchset #2 (id:20001) manually as
add53e33e773a0e1445a32b4b4289519ce745abf (presubmit successful).