equal doubles are not identical, NaNs are identical

[DartBot]

This issue was originally filed by [email protected]

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Spec v0.13 12.1 Constants reads:

identical() is the predefined dart function that returns true iff its two
arguments are either:
   • The same object.
   • Of type int and have the same numeric value.
   • Of type double, are not NaNs and have the same numeric value.

However, for the type double, VM violates both conditions:

• doubles with the same value, computated in different ways, are not identical.
• NaNs, computated in the same way, are identical.

Affected tests:
Language/11_Expressions/01_Constants_A18_t05
Language/11_Expressions/01_Constants_A18_t06

[kmillikin]

cc @fsc8000.
cc @sgmitrovic.

[lrhn]

As I read the spec, NaNs computed the same way may be the same object, and in that case should return true (from the first point - it's the same object).
This still breaks unboxing, so the first point should probably be conditioned by the objects not both being int and not both being double.

[anders-sandholm]

cc @gbracha.
Added Area-VM, Triaged labels.

[gbracha]

The spec needs some adjustment around NaNs. In fact, the VM team would like to change it, but we left it this way pending feedback from the dart2js team. The basic goal is to minimize surprises to the user. We were somewhat concerned about performance implications, but the VM testing indicates this is not a problem. WIth that in mind, I await feedback regarding dart2js.

[iposva-google]

Removed Priority-Medium label.
Added Priority-Unassigned label.

[iposva-google]

Set owner to @sgmitrovic.
Added Accepted label.

[ghost]

AFAIK this was fixed and resolved a while ago. The tests listed do not exist any longer

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Added AssumedStale label.