Get rid of old code for union/intersection in HType.

Get rid of old code for union/intersection in HType.

Introduce the concept of an empty type mask and use it to represent
both truly non-nullable empty masks (conflicting) and nullable 
empty masks (null).

Here are the differences (old ==> new) between the output of the union
and intersection operations when running all our tests:

Unchecked
=========
intersection(BoundedType(mask=[null|exact=JSExtendableArray]), indexable) :: readable array ==> extendable array
intersection(BoundedType(mask=[null|exact=JSFixedArray]), indexable) :: readable array ==> fixed array
intersection(BoundedType(mask=[null|exact=JSFixedArray]), mutable array) :: mutable array ==> fixed array
intersection(BoundedType(mask=[subclass=Object]), null type) :: null type ==> conflicting
intersection(BoundedType(mask=[subclass=Object]), String or null) :: String or null ==> String
intersection(BoundedType(mask=[subclass=Object]), unknown) :: unknown ==> BoundedType(mask=[subclass=Object])
intersection(BoundedType(mask=[subtype=Map]), unknown) :: BoundedType(mask=[subtype=Map]) ==> conflicting
intersection(unknown, BoundedType(mask=[subtype=Map])) :: BoundedType(mask=[subtype=Map]) ==> conflicting
intersection(unknown, BoundedType(mask=[subtype=SendPortSync])) :: BoundedType(mask=[subtype=SendPortSync]) ==> conflicting
union(integer or null, String) :: unknown ==> BoundedType(mask=[null|subtype=Comparable])
union(integer, String) :: unknown ==> BoundedType(mask=[subtype=Comparable])
union(null type, BoundedType(mask=[exact=Function])) :: unknown ==> BoundedType(mask=[null|exact=Function])
union(null type, BoundedType(mask=[exact=HashMap])) :: unknown ==> BoundedType(mask=[null|exact=HashMap])
union(null type, BoundedType(mask=[exact=_NativeJsSendPort])) :: unknown ==> BoundedType(mask=[null|exact=_NativeJsSendPort])
union(readable array, BoundedType(mask=[subclass=Iterable])) :: unknown ==> BoundedType(mask=[subtype=Iterable])

Checked
=======
intersection(BoundedType(mask=[null|exact=JSExtendableArray]), indexable) :: readable array ==> extendable array
intersection(BoundedType(mask=[null|exact=JSFixedArray]), indexable) :: readable array ==> fixed array
intersection(BoundedType(mask=[null|exact=JSFixedArray]), mutable array) :: mutable array ==> fixed array
intersection(BoundedType(mask=[null|subtype=_FutureErrorTest]), unknown) :: BoundedType(mask=[null|subtype=_FutureErrorTest]) ==> null type
intersection(BoundedType(mask=[null|subtype=_FutureOnError]), unknown) :: BoundedType(mask=[null|subtype=_FutureOnError]) ==> null type
intersection(BoundedType(mask=[subclass=Object]), null type) :: null type ==> conflicting
intersection(BoundedType(mask=[subclass=Object]), unknown) :: unknown ==> BoundedType(mask=[subclass=Object])
intersection(BoundedType(mask=[subtype=Map]), unknown) :: BoundedType(mask=[subtype=Map]) ==> conflicting
intersection(unknown, BoundedType(mask=[null|subtype=_CheckExceptionFn])) :: BoundedType(mask=[null|subtype=_CheckExceptionFn]) ==> null type
intersection(unknown, BoundedType(mask=[null|subtype=Function])) :: BoundedType(mask=[null|subtype=Function]) ==> null type
intersection(unknown, BoundedType(mask=[null|subtype=Object])) :: BoundedType(mask=[null|subtype=Object]) ==> unknown
intersection(unknown, BoundedType(mask=[null|subtype=void])) :: BoundedType(mask=[null|subtype=void]) ==> null type
intersection(unknown, BoundedType(mask=[subtype=Map])) :: BoundedType(mask=[subtype=Map]) ==> conflicting
intersection(unknown, BoundedType(mask=[subtype=SendPortSync])) :: BoundedType(mask=[subtype=SendPortSync]) ==> conflicting
union(integer or null, String) :: unknown ==> BoundedType(mask=[null|subtype=Comparable])
union(integer, String) :: unknown ==> BoundedType(mask=[subtype=Comparable])
union(null type, BoundedType(mask=[exact=HashMap])) :: unknown ==> BoundedType(mask=[null|exact=HashMap])
union(null type, BoundedType(mask=[exact=_NativeJsSendPort])) :: unknown ==> BoundedType(mask=[null|exact=_NativeJsSendPort])
union(number or null, BoundedType(mask=[null|subtype=Comparable])) :: unknown ==> BoundedType(mask=[null|subtype=Comparable])
union(number or null, String or null) :: unknown ==> BoundedType(mask=[null|subtype=Comparable])
union(readable array, BoundedType(mask=[subclass=Iterable])) :: unknown ==> BoundedType(mask=[subtype=Iterable])
union(String or null, number or null) :: unknown ==> BoundedType(mask=[null|subtype=Comparable])
union(String or null, number) :: unknown ==> BoundedType(mask=[null|subtype=Comparable])


R=ngeoffray@google.com
BUG=

Committed: https://code.google.com/p/dart/source/detail?r=19838

[kasperl, 2013-03-11 13:47:33]

On 2013/03/11 13:40:38, kasperl wrote:

The intersections with 'unknown' look a little bit weird. I'll double check that
everything behaves correctly.

[kasperl, 2013-03-11 13:53:37]

On 2013/03/11 13:47:33, kasperl wrote:
> On 2013/03/11 13:40:38, kasperl wrote:
> 
> The intersections with 'unknown' look a little bit weird. I'll double check
that
> everything behaves correctly.

So it looks like this is always happening when the type we're intersecting with
is 'unseen'. In that case, returning an empty/conflicting intersection is
actually ideal so I think this works just fine. We may want to create empty type
masks for checked mode types where the type is unseen...

[ngeoffray, 2013-03-11 14:52:28]

LGTM!

https://codereview.chromium.org/12764005/diff/5001/sdk/lib/_internal/compiler...
File sdk/lib/_internal/compiler/implementation/js_backend/emitter.dart (right):

https://codereview.chromium.org/12764005/diff/5001/sdk/lib/_internal/compiler...
sdk/lib/_internal/compiler/implementation/js_backend/emitter.dart:2046: if
(mask.isEmpty) continue;
Please add a comment that if the mask is JSNull, we know we don't need a
noSuchMethod on it.

https://codereview.chromium.org/12764005/diff/5001/sdk/lib/_internal/compiler...
File sdk/lib/_internal/compiler/implementation/ssa/types.dart (right):

https://codereview.chromium.org/12764005/diff/5001/sdk/lib/_internal/compiler...
sdk/lib/_internal/compiler/implementation/ssa/types.dart:46: if (isNullable) {
Please add a comment that this is to be backwards compatible and will be
removed.

https://codereview.chromium.org/12764005/diff/5001/sdk/lib/_internal/compiler...
File sdk/lib/_internal/compiler/implementation/types/type_mask.dart (right):

https://codereview.chromium.org/12764005/diff/5001/sdk/lib/_internal/compiler...
sdk/lib/_internal/compiler/implementation/types/type_mask.dart:76: return false;
Should it say false to JSNull? Also I guess the other variants below will say
false to JSNull as well. So the logic is handled else where? In
TypedSelector.applies?

[kasperl, 2013-03-12 05:56:56]

https://codereview.chromium.org/12764005/diff/5001/sdk/lib/_internal/compiler...
File sdk/lib/_internal/compiler/implementation/js_backend/emitter.dart (right):

https://codereview.chromium.org/12764005/diff/5001/sdk/lib/_internal/compiler...
sdk/lib/_internal/compiler/implementation/js_backend/emitter.dart:2046: if
(mask.isEmpty) continue;
On 2013/03/11 14:52:28, ngeoffray wrote:
> Please add a comment that if the mask is JSNull, we know we don't need a
> noSuchMethod on it.

Done.

https://codereview.chromium.org/12764005/diff/5001/sdk/lib/_internal/compiler...
File sdk/lib/_internal/compiler/implementation/ssa/types.dart (right):

https://codereview.chromium.org/12764005/diff/5001/sdk/lib/_internal/compiler...
sdk/lib/_internal/compiler/implementation/ssa/types.dart:46: if (isNullable) {
On 2013/03/11 14:52:28, ngeoffray wrote:
> Please add a comment that this is to be backwards compatible and will be
> removed.

Done.

https://codereview.chromium.org/12764005/diff/5001/sdk/lib/_internal/compiler...
File sdk/lib/_internal/compiler/implementation/types/type_mask.dart (right):

https://codereview.chromium.org/12764005/diff/5001/sdk/lib/_internal/compiler...
sdk/lib/_internal/compiler/implementation/types/type_mask.dart:76: return false;
On 2013/03/11 14:52:28, ngeoffray wrote:
> Should it say false to JSNull? Also I guess the other variants below will say
> false to JSNull as well. So the logic is handled else where? In
> TypedSelector.applies?

I'll try to move more of the code from TypedSelector.applies into the TypeMask
class so maybe this can be simplified. Right now, I'm dealing with null through
the isNullable flag and I think I'd prefer to avoid using JSNull in too many
places.

[kasperl, 2013-03-12 05:59:50]

Committed patchset #3 manually as r19838 (presubmit successful).