VM [KERNEL] Elide null-initialization of the fields

VM [KERNEL] Elide null-initialization of the fields

They are filled with nulls after allocation, so there is
no need to set a field to null explicitly.

R=vegorov@google.com

Committed: https://github.com/dart-lang/sdk/commit/82beee09c2bc537afd3438ed88a1387d6c36e62b

[Dmitry Olshansky, 2017-03-30 13:25:05]

dmitryolsh@google.com changed reviewers:
+ kustermann@google.com, vegorov@google.com

[Florian Schneider, 2017-03-30 19:42:58]

fschneider@google.com changed reviewers:
+ fschneider@google.com

[Florian Schneider, 2017-03-30 19:42:59]

https://codereview.chromium.org/2790603002/diff/1/runtime/vm/kernel_to_il.cc
File runtime/vm/kernel_to_il.cc (right):

https://codereview.chromium.org/2790603002/diff/1/runtime/vm/kernel_to_il.cc#...
runtime/vm/kernel_to_il.cc:4094: return elide_initialization ? Fragment() :
instructions;
dbc: If the explicit store is not present, you have to record the null-store
using Field::RecordStore for field type guards:

field.RecordStore(Object::null_object());

We do that in the parser in all places where we don't emit an explicit field
initializer.

[Dmitry Olshansky, 2017-03-31 14:19:50]

https://codereview.chromium.org/2790603002/diff/1/runtime/vm/kernel_to_il.cc
File runtime/vm/kernel_to_il.cc (right):

https://codereview.chromium.org/2790603002/diff/1/runtime/vm/kernel_to_il.cc#...
runtime/vm/kernel_to_il.cc:4094: return elide_initialization ? Fragment() :
instructions;
On 2017/03/30 19:42:59, Florian Schneider wrote:
> dbc: If the explicit store is not present, you have to record the null-store
> using Field::RecordStore for field type guards:
> 
> field.RecordStore(Object::null_object());
> 
> We do that in the parser in all places where we don't emit an explicit field
> initializer.

Done.

[Dmitry Olshansky, 2017-03-31 14:44:41]

Redone to avoid generating IL for the null literal case.

[Vyacheslav Egorov (Google), 2017-03-31 15:00:57]

lgtm

https://codereview.chromium.org/2790603002/diff/20001/runtime/vm/kernel_to_il.cc
File runtime/vm/kernel_to_il.cc (right):

https://codereview.chromium.org/2790603002/diff/20001/runtime/vm/kernel_to_il...
runtime/vm/kernel_to_il.cc:4083: Fragment initializer =
TranslateExpression(init);
Better init->IsNullLiteral() instead of this.

[Dmitry Olshansky, 2017-03-31 15:49:49]

Description was changed from

==========
VM [KERNEL] Elide null-initialization of the fields

They are filled with nulls after allocation, so there is
no need to set a field to null explicitly.
==========

to

==========
VM [KERNEL] Elide null-initialization of the fields

They are filled with nulls after allocation, so there is
no need to set a field to null explicitly.

R=vegorov@google.com

Committed:
https://github.com/dart-lang/sdk/commit/82beee09c2bc537afd3438ed88a1387d6c36e62b
==========

[Dmitry Olshansky, 2017-03-31 15:49:51]

Committed patchset #3 (id:40001) manually as
82beee09c2bc537afd3438ed88a1387d6c36e62b (presubmit successful).