More compact string representation on 64 bit.

More compact string representation on 64 bit.

This moves the hash code into the header word for strings on 64 bit
platforms.  With the old layout, 9 character strings became 48-byte
objects.  With the new layout you have to go to 17 characters before
you are bumped from 4 to 6 words (32 to 48 bytes).

As a side effect, the class ID field is now 16 bits on all platforms
instead of having two different sizes, and the size field is 8 bits
on all platforms.

This also paves the way for moving the hash code for instance objects
into the header, so we won't need the side-lookup in the
hash-table-of-hash-codes on 64 bit platforms.

This is a reapplication of https://codereview.chromium.org/2893553002/
after issues were fixed in https://codereview.chromium.org/2888413002/
and https://codereview.chromium.org/2896583002/

R=vegorov@google.com
BUG=

Committed: https://github.com/dart-lang/sdk/commit/aa60a2ea90d9d2c7f9ba58da15592763f291ce93

[Vyacheslav Egorov (Google), 2017-05-22 07:54:52]

rubberstamp lgtm

(assuming that this is just a reapplication with no changes)

[erikcorry, 2017-05-22 08:05:35]

Description was changed from

==========
More compact string representation on 64 bit.

This moves the hash code into the header word for strings on 64 bit
platforms.  With the old layout, 9 character strings became 48-byte
objects.  With the new layout you have to go to 17 characters before
you are bumped from 4 to 6 words (32 to 48 bytes).

As a side effect, the class ID field is now 16 bits on all platforms
instead of having two different sizes, and the size field is 8 bits
on all platforms.

This also paves the way for moving the hash code for instance objects
into the header, so we won't need the side-lookup in the
hash-table-of-hash-codes on 64 bit platforms.

This is a reapplication of https://codereview.chromium.org/2893553002/
after issues were fixed in https://codereview.chromium.org/2888413002/
and https://codereview.chromium.org/2896583002/

R=vegorov@google.com
BUG=
==========

to

==========
More compact string representation on 64 bit.

This moves the hash code into the header word for strings on 64 bit
platforms.  With the old layout, 9 character strings became 48-byte
objects.  With the new layout you have to go to 17 characters before
you are bumped from 4 to 6 words (32 to 48 bytes).

As a side effect, the class ID field is now 16 bits on all platforms
instead of having two different sizes, and the size field is 8 bits
on all platforms.

This also paves the way for moving the hash code for instance objects
into the header, so we won't need the side-lookup in the
hash-table-of-hash-codes on 64 bit platforms.

This is a reapplication of https://codereview.chromium.org/2893553002/
after issues were fixed in https://codereview.chromium.org/2888413002/
and https://codereview.chromium.org/2896583002/

R=vegorov@google.com
BUG=

Committed:
https://github.com/dart-lang/sdk/commit/aa60a2ea90d9d2c7f9ba58da15592763f291ce93
==========

[erikcorry, 2017-05-22 08:06:07]

Committed patchset #1 (id:1) manually as
aa60a2ea90d9d2c7f9ba58da15592763f291ce93 (presubmit successful).