Roslyn: Suboptimal code for e is null

[alrz]

Currently e is null translates to an object.Equals call on master. The question is that (1) does it meant to be a shorthand for explicit reference null check (object)e == null? If so, (2) shouldn't it just translate to a ceq?

[orthoxerox]

What if e is a nullable value type? But I agree, the compiler can check this at compile time and emit better code for reference types.

[gafter]

@alrz they should generate the same code

[alrz]

@gafter if so, I think this covers #8409 unless you have two non-constant expressions.

[jaredpar]

Moving out for now as this doesn't meet the RTM bar.

[gafter]

Did you want to move #16129 out too?

[gafter]

Also #14252

[jaredpar]

Yes and Yes. Thanks!

[sharwell]

:bulb: See #19803 for a very descriptive breakdown of the current and expected behavior for both Nullable<T> and reference types.