dart2js cps: Compile some loops as 'for' loops.

dart2js cps: Compile some loops as 'for' loops.

BUG=
R=kmillikin@google.com

Committed: https://github.com/dart-lang/sdk/commit/296cb0b5b45575f9e32acd2cbad2b8969e56cb77

Committed: https://github.com/dart-lang/sdk/commit/01844e7bb01d0c2eff1ef6301b0859eeda1222e0

[asgerf, 2015-08-13 09:15:22]

asgerf@google.com changed reviewers:
+ kmillikin@google.com

[Kevin Millikin (Google), 2015-08-13 11:32:48]

GLTM.

https://codereview.chromium.org/1287253002/diff/1/pkg/compiler/lib/src/tree_i...
File pkg/compiler/lib/src/tree_ir/optimization/loop_rewriter.dart (right):

https://codereview.chromium.org/1287253002/diff/1/pkg/compiler/lib/src/tree_i...
pkg/compiler/lib/src/tree_ir/optimization/loop_rewriter.dart:182: int
assignIndex = 0;
Seems kind of tricky that this might be one past the end of the list, though the
code below handles that case properly.  Might be worth mentioning that it is
intentional and indicates no eligible assignment.

It seems more natural to me to iterate in reverse searching for the first
non-assignment.  That allows an early exit too:

int assignIndex = statements.length;
while (assignIndex > 0 && statements[assignIndex - 1) is! Assign) {
  --assignIndex;
}

(But my code is untested.)

https://codereview.chromium.org/1287253002/diff/1/pkg/compiler/lib/src/tree_i...
File pkg/compiler/lib/src/tree_ir/tree_ir_nodes.dart (right):

https://codereview.chromium.org/1287253002/diff/1/pkg/compiler/lib/src/tree_i...
pkg/compiler/lib/src/tree_ir/tree_ir_nodes.dart:510: class WhileCondition
extends Loop {
Strange that While has updates.  Maybe we call it For.

[Kevin Millikin (Google), 2015-08-13 11:33:05]

LGTM also.

[asgerf, 2015-08-13 12:06:42]

https://codereview.chromium.org/1287253002/diff/1/pkg/compiler/lib/src/tree_i...
File pkg/compiler/lib/src/tree_ir/optimization/loop_rewriter.dart (right):

https://codereview.chromium.org/1287253002/diff/1/pkg/compiler/lib/src/tree_i...
pkg/compiler/lib/src/tree_ir/optimization/loop_rewriter.dart:182: int
assignIndex = 0;
On 2015/08/13 11:32:47, Kevin Millikin (Google) wrote:
> Seems kind of tricky that this might be one past the end of the list, though
the
> code below handles that case properly.  Might be worth mentioning that it is
> intentional and indicates no eligible assignment.
> 
> It seems more natural to me to iterate in reverse searching for the first
> non-assignment.  That allows an early exit too:
> 
> int assignIndex = statements.length;
> while (assignIndex > 0 && statements[assignIndex - 1) is! Assign) {
>   --assignIndex;
> }
> 
> (But my code is untested.)

Yeah that looks better. Done.

https://codereview.chromium.org/1287253002/diff/1/pkg/compiler/lib/src/tree_i...
File pkg/compiler/lib/src/tree_ir/tree_ir_nodes.dart (right):

https://codereview.chromium.org/1287253002/diff/1/pkg/compiler/lib/src/tree_i...
pkg/compiler/lib/src/tree_ir/tree_ir_nodes.dart:510: class WhileCondition
extends Loop {
On 2015/08/13 11:32:47, Kevin Millikin (Google) wrote:
> Strange that While has updates.  Maybe we call it For.

Renamed.

[asgerf, 2015-08-14 10:09:36]

Committed patchset #3 (id:40001) manually as
296cb0b5b45575f9e32acd2cbad2b8969e56cb77 (presubmit successful).

[asgerf, 2015-08-17 08:52:40]

Committed patchset #5 (id:80001) manually as
01844e7bb01d0c2eff1ef6301b0859eeda1222e0 (presubmit successful).