Fix incorrect desugaring of cascades.

Fix incorrect desugaring of cascades.

Make use of the attractive and powerful way that the LoadLocal expression is
really a pair of an arbitrary statement and a local variable load.

BUG=dart:7494
Committed: https://code.google.com/p/dart/source/detail?r=16684

[srdjan, 2013-01-04 16:14:39]

lgtm

[Ivan Posva, 2013-01-04 17:31:56]

DBC -ip

https://codereview.chromium.org/11745028/diff/1/runtime/vm/parser.cc
File runtime/vm/parser.cc (right):

https://codereview.chromium.org/11745028/diff/1/runtime/vm/parser.cc#newcode6915
runtime/vm/parser.cc:6915: SequenceNode* cascade = new SequenceNode(cascade_pos,
NULL);
Can you please explain why this is not a hack? You make it sound as if the
LoadLocal can overtake the StoreLocal here in general, which makes me nervous.

Adding a comment to the creation of the SequenceNode would help, thanks.

[Kevin Millikin (Google), 2013-01-07 09:14:13]

https://codereview.chromium.org/11745028/diff/1/runtime/vm/parser.cc
File runtime/vm/parser.cc (right):

https://codereview.chromium.org/11745028/diff/1/runtime/vm/parser.cc#newcode6915
runtime/vm/parser.cc:6915: SequenceNode* cascade = new SequenceNode(cascade_pos,
NULL);
On 2013/01/04 17:31:56, Ivan Posva wrote:
> Can you please explain why this is not a hack? You make it sound as if the
> LoadLocal can overtake the StoreLocal here in general, which makes me nervous.
> 
> Adding a comment to the creation of the SequenceNode would help, thanks.

I think it is a hack.  I'll add a comment here, at the other use, and in the
LoadLocal AST class explaining it.