dart2js cps: Hoist loop-invariant branches from loop entry.

dart2js cps: Hoist loop-invariant branches from loop entry.

Performs the following optimization:

  b = COND
  while (true) {
    if (b)
      BRANCH (contains no continue to loop)
    else
      LOOP
  }

==>

  b = COND
  if (b)
    BRANCH
  else
    while (true)
      LOOP

BUG=
R=sra@google.com

Committed: https://github.com/dart-lang/sdk/commit/41412aaa70f5c5af51e7d35ed5237a42d7c6b8d9

[asgerf, 2016-01-08 23:42:41]

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

[Siggi Cherem (dart-lang), 2016-01-08 23:51:34]

minor drive-by comment

https://codereview.chromium.org/1573693002/diff/1/pkg/compiler/lib/src/cps_ir...
File pkg/compiler/lib/src/cps_ir/cps_fragment.dart (right):

https://codereview.chromium.org/1573693002/diff/1/pkg/compiler/lib/src/cps_ir...
pkg/compiler/lib/src/cps_ir/cps_fragment.dart:13: import 'cps_fragment.dart';
remove self import?

[sra1, 2016-01-09 01:07:14]

lgtm

https://codereview.chromium.org/1573693002/diff/1/pkg/compiler/lib/src/cps_ir...
File pkg/compiler/lib/src/cps_ir/loop_invariant_branch.dart (right):

https://codereview.chromium.org/1573693002/diff/1/pkg/compiler/lib/src/cps_ir...
pkg/compiler/lib/src/cps_ir/loop_invariant_branch.dart:98: /// This only works
because [AlphaRenamer] cleans up after this pass.
'after this pass' -> 'at the end of this pass'.

https://codereview.chromium.org/1573693002/diff/1/pkg/compiler/lib/src/cps_ir...
pkg/compiler/lib/src/cps_ir/loop_invariant_branch.dart:131: // Check if this is
a loop starting with a branch.
It would be nice if there was a quick way to test this before computing
loopHierarchy.

[asgerf, 2016-01-11 18:06:42]

Description was changed from

==========
dart2js cps: Hoist loop-invariant branches from loop entry.

Performs the following optimization:

  b = COND
  while (true) {
    if (b)
      BRANCH (contains no continue to loop)
    else
      LOOP
  }

==>

  b = COND
  if (b)
    BRANCH
  else
    while (true)
      LOOP

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

to

==========
dart2js cps: Hoist loop-invariant branches from loop entry.

Performs the following optimization:

  b = COND
  while (true) {
    if (b)
      BRANCH (contains no continue to loop)
    else
      LOOP
  }

==>

  b = COND
  if (b)
    BRANCH
  else
    while (true)
      LOOP

BUG=
R=sra@google.com

Committed:
https://github.com/dart-lang/sdk/commit/41412aaa70f5c5af51e7d35ed5237a42d7c6b8d9
==========

[asgerf, 2016-01-11 18:06:43]

Committed patchset #2 (id:20001) manually as
41412aaa70f5c5af51e7d35ed5237a42d7c6b8d9 (presubmit successful).

[asgerf, 2016-01-11 19:07:07]

https://codereview.chromium.org/1573693002/diff/1/pkg/compiler/lib/src/cps_ir...
File pkg/compiler/lib/src/cps_ir/cps_fragment.dart (right):

https://codereview.chromium.org/1573693002/diff/1/pkg/compiler/lib/src/cps_ir...
pkg/compiler/lib/src/cps_ir/cps_fragment.dart:13: import 'cps_fragment.dart';
On 2016/01/08 23:51:34, Siggi Cherem (dart-lang) wrote:
> remove self import?

I must have been confused when I wrote that

https://codereview.chromium.org/1573693002/diff/1/pkg/compiler/lib/src/cps_ir...
File pkg/compiler/lib/src/cps_ir/loop_invariant_branch.dart (right):

https://codereview.chromium.org/1573693002/diff/1/pkg/compiler/lib/src/cps_ir...
pkg/compiler/lib/src/cps_ir/loop_invariant_branch.dart:98: /// This only works
because [AlphaRenamer] cleans up after this pass.
On 2016/01/09 01:07:14, sra1 wrote:
> 'after this pass' -> 'at the end of this pass'.

Sorry, I thought I fixed this. I'll put up another CL for it.

https://codereview.chromium.org/1573693002/diff/1/pkg/compiler/lib/src/cps_ir...
pkg/compiler/lib/src/cps_ir/loop_invariant_branch.dart:131: // Check if this is
a loop starting with a branch.
On 2016/01/09 01:07:14, sra1 wrote:
> It would be nice if there was a quick way to test this before computing
> loopHierarchy.

Acknowledged.