Make the mutable variables local to an IR builder instead of global.

Make the mutable variables local to an IR builder instead of global.

When translating a try block, variables become mutable on entry and stop
being mutable on exit.  Make the set of set of mutable variables local to an
IR builder instead of global for a whole function, so that the translation
does not depend so heavily on the order of visiting subparts of the input.

Since JS code can have mutable variables (i.e., not boxed in the heap), move
them to the backend-independent IR builder state.  This fixes a bug in the
JS translation of try-catch where the environment would contain duplicated
bindings for mutable variables.  The right binding happened to 'win' so it
was not observable other than an assertion failure.

BUG=
R=asgerf@google.com

Committed: https://code.google.com/p/dart/source/detail?r=45272

Committed: https://code.google.com/p/dart/source/detail?r=45279

[Kevin Millikin (Google), 2015-04-17 13:43:59]

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

[asgerf, 2015-04-20 08:46:10]

LGTM

https://codereview.chromium.org/1080003005/diff/1/pkg/compiler/lib/src/cps_ir...
File pkg/compiler/lib/src/cps_ir/cps_ir_builder.dart (right):

https://codereview.chromium.org/1080003005/diff/1/pkg/compiler/lib/src/cps_ir...
pkg/compiler/lib/src/cps_ir/cps_ir_builder.dart:2136:
dartState.registerizedMutableVariables.add(loopVariable);
We should be able to get rid of registerizedMutableVariables now. I never liked
it anyway. But it's low priority so I'm fine with doing that later.

[Kevin Millikin (Google), 2015-04-20 09:00:21]

Committed patchset #1 (id:1) manually as 45272 (presubmit successful).

[Kevin Millikin (Google), 2015-04-20 10:32:20]

I should have run dart2dart tests.  I've fixed a pair of bugs.  Please take a
quick look at the diff between patch sets 1 and 2.

https://codereview.chromium.org/1080003005/diff/20001/pkg/compiler/lib/src/cp...
File pkg/compiler/lib/src/cps_ir/cps_ir_builder.dart (right):

https://codereview.chromium.org/1080003005/diff/20001/pkg/compiler/lib/src/cp...
pkg/compiler/lib/src/cps_ir/cps_ir_builder.dart:577: new Map<Local,
ir.MutableVariable>.from(mutableVariables);
Inner function builders need to inherit the mutable variables of the outer
builder.  (In JS there are no references to any of them --- if there were a
reference from an inner function then it would be boxed in the heap and not a
mutable variable.)

https://codereview.chromium.org/1080003005/diff/20001/pkg/compiler/lib/src/cp...
pkg/compiler/lib/src/cps_ir/cps_ir_builder.dart:2081: : dartState = new
DartIrBuilderSharedState() {
There should be only one of these, not one per builder.  As you noted, it
contains only the registerized variables that we don't really need any more.

[asgerf, 2015-04-20 10:48:50]

lgtm

[Kevin Millikin (Google), 2015-04-20 11:44:32]

Committed patchset #2 (id:20001) manually as 45279 (presubmit successful).