Single.GetHashCode should be marked AgressiveInlining

[billwert]

A change (dotnet/coreclr#18645) affected the inlining decision for Single.GetHashCode. Double.GetHashCode is marked AgressiveInlining, and so should Single.

This surfaces as a perf regression in one of our tests for Vector2 and Vector3.

Method	Toolchain	Mean
GetHashCodeBenchmark	netcoreapp2.2	2.336 ns
GetHashCodeBenchmark	netcoreapp3.0	4.509 ns

[danmoseley]

Because it's now a readonly struct? Is there an issue to fix the inlining decision so customers don't have to annotate in this way?

[AndyAyersMS]

No, this is not directly related to readonly: dotnet/coreclr#18645 made the IL for Single.GetHashCode larger and more complex than it was in 2.2, and so it no longer inlines without a nudge.

[mikedn]

Also note that Double.GetHashCode is already aggressive inlined, that one generates even larger code. In both cases there are some JIT tweaks that could be made to make the generates native code slightly smaller, just to further skew the inliner's native code size estimates :)