dart2js cps: Make register allocation prioritize phi elimination.

dart2js cps: Make register allocation prioritize phi elimination.

The variable merger pass now prioritizes register allocations that
remove a moving assignment "v1 = v2" or enable a compoundable assignment
"v1 = v2 + E" to become "v1_2 += E".

When minifying, we now allow merging differently named variables.
Previously, preserving the variable names was important to get a good
register allocation, but that heuristic is no longer needed.

BUG=
R=kmillikin@google.com

Committed: https://github.com/dart-lang/sdk/commit/a1121d1488ff1bd1f1f739499a408a867a6eb69d

[asgerf, 2016-01-22 22:56:10]

Description was changed from

==========
dart2js cps: Make register allocation prioritize phi elimination.

The variable merger pass now prioritizes register allocations that
remove a moving assignment "v1 = v2" or enable a compoundable assignment
"v1 = v2 + E" to become "v1_2 += E".

When minifying, we now allow merging differently named variables.
Previously, preserving the variable names was important to get a good
register allocation, but the register allocator is smart enough on its
own now.

BUG=
==========

to

==========
dart2js cps: Make register allocation prioritize phi elimination.

The variable merger pass now prioritizes register allocations that
remove a moving assignment "v1 = v2" or enable a compoundable assignment
"v1 = v2 + E" to become "v1_2 += E".

When minifying, we now allow merging differently named variables.
Previously, preserving the variable names was important to get a good
register allocation, but that heuristic is no longer needed.

BUG=
==========

[asgerf, 2016-01-22 23:00:45]

asgerf@google.com changed reviewers:
+ kmillikin@google.com, sigmund@google.com, sra@google.com

[Kevin Millikin (Google), 2016-01-26 08:27:26]

lgtm

https://codereview.chromium.org/1625643002/diff/20001/pkg/compiler/lib/src/tr...
File pkg/compiler/lib/src/tree_ir/optimization/variable_merger.dart (right):

https://codereview.chromium.org/1625643002/diff/20001/pkg/compiler/lib/src/tr...
pkg/compiler/lib/src/tree_ir/optimization/variable_merger.dart:20:
VariableMerger({this.minifying});
Is this an optional parameter, or merely named?  It seems a bit more clear to me
to have a non-null default value (I suggest false).

[asgerf, 2016-01-26 09:07:38]

https://codereview.chromium.org/1625643002/diff/20001/pkg/compiler/lib/src/tr...
File pkg/compiler/lib/src/tree_ir/optimization/variable_merger.dart (right):

https://codereview.chromium.org/1625643002/diff/20001/pkg/compiler/lib/src/tr...
pkg/compiler/lib/src/tree_ir/optimization/variable_merger.dart:20:
VariableMerger({this.minifying});
On 2016/01/26 08:27:26, Kevin Millikin (Google) wrote:
> Is this an optional parameter, or merely named?  It seems a bit more clear to
me
> to have a non-null default value (I suggest false).

Set default to false.

[asgerf, 2016-01-26 11:28:30]

Description was changed from

==========
dart2js cps: Make register allocation prioritize phi elimination.

The variable merger pass now prioritizes register allocations that
remove a moving assignment "v1 = v2" or enable a compoundable assignment
"v1 = v2 + E" to become "v1_2 += E".

When minifying, we now allow merging differently named variables.
Previously, preserving the variable names was important to get a good
register allocation, but that heuristic is no longer needed.

BUG=
==========

to

==========
dart2js cps: Make register allocation prioritize phi elimination.

The variable merger pass now prioritizes register allocations that
remove a moving assignment "v1 = v2" or enable a compoundable assignment
"v1 = v2 + E" to become "v1_2 += E".

When minifying, we now allow merging differently named variables.
Previously, preserving the variable names was important to get a good
register allocation, but that heuristic is no longer needed.

BUG=
R=kmillikin@google.com

Committed:
https://github.com/dart-lang/sdk/commit/a1121d1488ff1bd1f1f739499a408a867a6eb69d
==========

[asgerf, 2016-01-26 11:28:31]

Committed patchset #3 (id:40001) manually as
a1121d1488ff1bd1f1f739499a408a867a6eb69d (presubmit successful).