Subzero: Add a new document describing the register allocator.

Subzero: Add a new document describing the register allocator.

There's some good work in Subzero's register allocation, which deserves to be captured in a single place.

BUG= none
R=kschimpf@google.com

Committed: https://gerrit.chromium.org/gerrit/gitweb?p=native_client/pnacl-subzero.git;a=commit;h=59b0dad77008c3f053c2675bde5d98fc9f825ea8

[Jim Stichnoth, 2016-08-23 23:54:47]

Description was changed from

==========
Subzero: Add a new document describing the register allocator.

BUG= none
==========

to

==========
Subzero: Add a new document describing the register allocator.

There's some good work in Subzero's register allocation, which deserves to be
captured in a single place.

BUG= none
==========

[Jim Stichnoth, 2016-08-23 23:54:47]

stichnot@chromium.org changed reviewers:
+ eholk@chromium.org, jpp@chromium.org, kschimpf@google.com

[John, 2016-08-24 14:13:58]

It would be nice to have someone other than us read this to see if they
understand the documentation (maybe jacob, jgravelle@ ?)

https://codereview.chromium.org/2277493003/diff/1/docs/REGALLOC.rst
File docs/REGALLOC.rst (right):

https://codereview.chromium.org/2277493003/diff/1/docs/REGALLOC.rst#newcode371
docs/REGALLOC.rst:371: pass over the instructions in a block.  Every time a
variable ``V`` is
I don't understand how this leads to a chain

V'' -> V' -> V

Also, what happens to register allocated variables? When/how is its value
merged?

[Jim Stichnoth, 2016-08-25 13:28:40]

https://codereview.chromium.org/2277493003/diff/1/docs/REGALLOC.rst
File docs/REGALLOC.rst (right):

https://codereview.chromium.org/2277493003/diff/1/docs/REGALLOC.rst#newcode371
docs/REGALLOC.rst:371: pass over the instructions in a block.  Every time a
variable ``V`` is
On 2016/08/24 14:13:58, John wrote:
> I don't understand how this leads to a chain
> 
> V'' -> V' -> V

I was a bit lazy writing this paragraph, and so I've updated it to be more
precise.

> 
> Also, what happens to register allocated variables? When/how is its value
> merged?

By "register allocated variables", do you mean *must-have-register* variables
(using the terminology from this doc)?  i.e. infinite-weight or pre-colored.  I
updated the paragraph to say this is just done for *may-have-register*
variables.

I'm not sure what you mean by "merged", since one point of block-local splitting
is to avoid any merge issues across basic blocks.

[Jim Stichnoth, 2017-02-01 16:51:01]

Any objections to just landing this as currently is?

[Karl, 2017-02-01 16:52:18]

lgtm

[Jim Stichnoth, 2017-02-01 17:03:13]

Description was changed from

==========
Subzero: Add a new document describing the register allocator.

There's some good work in Subzero's register allocation, which deserves to be
captured in a single place.

BUG= none
==========

to

==========
Subzero: Add a new document describing the register allocator.

There's some good work in Subzero's register allocation, which deserves to be
captured in a single place.

BUG= none
R=kschimpf@google.com

Committed:
https://gerrit.chromium.org/gerrit/gitweb?p=native_client/pnacl-subzero.git;a...
==========

[Jim Stichnoth, 2017-02-01 17:03:16]

Committed patchset #2 (id:20001) manually as
59b0dad77008c3f053c2675bde5d98fc9f825ea8 (presubmit successful).