Use a shared function to represent type substitutions with dynamic.

Use a shared function to represent type substitutions with dynamic.

BUG=
R=floitsch@google.com

Committed: https://code.google.com/p/dart/source/detail?r=43000

[herhut, 2015-01-13 14:17:03]

herhut@google.com changed reviewers:
+ floitsch@google.com, karlklose@google.com

[floitsch, 2015-01-13 17:45:24]

Not completely happy with the solution yet.

https://codereview.chromium.org/826413003/diff/1/pkg/compiler/lib/src/js_back...
File pkg/compiler/lib/src/js_backend/runtime_types.dart (right):

https://codereview.chromium.org/826413003/diff/1/pkg/compiler/lib/src/js_back...
pkg/compiler/lib/src/js_backend/runtime_types.dart:886: return js('#.#',
[rti.backend.namer.isolateName,
This will break in the new emitter.
The runtime_types.dart file should not need to know how the emitter stores
things.
Just looking at this file it makes absolutely no sense that we look for
something on isolateName.X.

Several options:
- 1. we guarantee that (some) embedded globals are set up early enough. In that
case you would ask the emitter for the embedded global
"FUNCTION_THAT_RETURNS_NULL".
- 2. the `getCode` function receives a jsAst as argument. Makes it very clear
what happens, but doesn't allow the caller to see if it was actually used.
- 3. `getCode` asks the emitter for a reference to the null-function.

[herhut, 2015-01-15 10:43:02]

https://codereview.chromium.org/826413003/diff/1/pkg/compiler/lib/src/js_back...
File pkg/compiler/lib/src/js_backend/runtime_types.dart (right):

https://codereview.chromium.org/826413003/diff/1/pkg/compiler/lib/src/js_back...
pkg/compiler/lib/src/js_backend/runtime_types.dart:886: return js('#.#',
[rti.backend.namer.isolateName,
On 2015/01/13 17:45:24, floitsch wrote:
> This will break in the new emitter.
> The runtime_types.dart file should not need to know how the emitter stores
> things.
> Just looking at this file it makes absolutely no sense that we look for
> something on isolateName.X.
> 
> Several options:
> - 1. we guarantee that (some) embedded globals are set up early enough. In
that
> case you would ask the emitter for the embedded global
> "FUNCTION_THAT_RETURNS_NULL".
> - 2. the `getCode` function receives a jsAst as argument. Makes it very clear
> what happens, but doesn't allow the caller to see if it was actually used.
> - 3. `getCode` asks the emitter for a reference to the null-function.

I have opted for 3. The emitter now has a [generateFunctionThatReturnsNull]
helper and it is up to the emitter to do the best thing. The old emitter uses a
single reference stored on Isolate (in lack of a better place) but the new
emitter still creates a new function every time.

[floitsch, 2015-01-16 16:56:13]

LGTM.

https://codereview.chromium.org/826413003/diff/20001/pkg/compiler/lib/src/js_...
File pkg/compiler/lib/src/js_emitter/new_emitter/emitter.dart (right):

https://codereview.chromium.org/826413003/diff/20001/pkg/compiler/lib/src/js_...
pkg/compiler/lib/src/js_emitter/new_emitter/emitter.dart:78: return
js.js(r"""function() { return null; }""");
Could we make this return `undefined` ?
Would make the function smaller...

No need for triple quotes.

[herhut, 2015-01-20 09:42:10]

Committed patchset #3 (id:40001) manually as 43000 (presubmit successful).

[karlklose, 2015-01-20 10:37:32]

https://codereview.chromium.org/826413003/diff/40001/pkg/compiler/lib/src/js_...
File pkg/compiler/lib/src/js_backend/runtime_types.dart (right):

https://codereview.chromium.org/826413003/diff/40001/pkg/compiler/lib/src/js_...
pkg/compiler/lib/src/js_backend/runtime_types.dart:36: =>
backend.namer.getMappedInstanceName('functionThatReturnsNull');
Use {} when it does not fit on a line.

How about 'nameOfFunctionThatReturnsNull'? I find that easier to understand.

https://codereview.chromium.org/826413003/diff/40001/pkg/compiler/lib/src/js_...
File pkg/compiler/lib/src/js_emitter/old_emitter/emitter.dart (right):

https://codereview.chromium.org/826413003/diff/40001/pkg/compiler/lib/src/js_...
pkg/compiler/lib/src/js_emitter/old_emitter/emitter.dart:934: jsAst.Expression
generateFunctionThatReturnsNull() {
This generates code to access the function, not the function itself.

https://codereview.chromium.org/826413003/diff/40001/sdk/lib/_internal/compil...
File sdk/lib/_internal/compiler/js_lib/js_rti.dart (right):

https://codereview.chromium.org/826413003/diff/40001/sdk/lib/_internal/compil...
sdk/lib/_internal/compiler/js_lib/js_rti.dart:40: *     a list expression. The
function may also return null, which is equivalent
"null" -> "`null`".