Unsafe.SizeOf<T>() causes an additional mov over sizeof(T)

[MichalPetryka]

Description

In some cases, Unsafe.SizeOf<T> produces an additional mov over sizeof(T) (both over not compile time known types).

Configuration

Sharplab Core CLR v5.0.721.25508

Regression?

No idea.

Data

Sharplab

I couldn't figure out the best area label to add to this issue. If you have write-permissions please help me learn by adding exactly one area label.

[GrabYourPitchforks]

@jkotas There's an existing proposal to move the Unsafe type down to corelib. Might this issue be resolved as a side effect of that work?

[jkotas]

proposal to move the Unsafe type down to corelib.

... and turn it into JIT intrinsic. I agree that turning Unsafe into JIT intrinsic is likely to fix this issue.

[AndyAyersMS]

Also likely to be fixed if/when we implement forward sub (#6973)