Refactor HCheckInstanceType to allow mask/tag tests.

Refactor HCheckInstanceType to allow mask/tag tests.

This allows us to get rid of totally fake LAST_STRING_TYPE and makes
it possible to test for symbols.

I considered splitting HCheckInstanceType into two instructions, but
it seems nice to be able to hide the instance type implementation
details from the hydrogen level.

Committed: http://code.google.com/p/v8/source/detail?r=7840

[Mads Ager (chromium), 2011-05-09 16:57:51]

Can we split this into two different hydrogen instructions (potentially with a
shared super class)?

The rest looks good to me.

http://codereview.chromium.org/6964011/diff/1/src/hydrogen-instructions.h
File src/hydrogen-instructions.h (right):

http://codereview.chromium.org/6964011/diff/1/src/hydrogen-instructions.h#new...
src/hydrogen-instructions.h:1831: // Check that the instance type is in the
range [first, last] where
Comment needs updating.

http://codereview.chromium.org/6964011/diff/1/src/hydrogen-instructions.h#new...
src/hydrogen-instructions.h:1851: uint8_t mask_;
I don't like this much. Create two types of instructions instead of having two
unused fields per instance?

[Mads Ager (chromium), 2011-05-10 13:41:42]

LGTM, I like this approach better, thanks.