Inline GetAlternateLookup

[bitfaster]

Inlining GetAlternateLookup eliminates the heap allocation for the AlternateLookup struct on .NET 10:

Method	Runtime	Mean	Ratio	Gen0	Allocated
GetAlternateInline	.NET 10.0	42.73 ns	0.77	-	-
GetAlternateNoInline	.NET 10.0	52.94 ns	0.96	0.0092	40 B
GetAlternateInline	.NET 9.0	55.35 ns	1.00	0.0092	40 B
GetAlternateNoInline	.NET 9.0	56.13 ns	1.01	0.0092	40 B

From https://learn.microsoft.com/en-us/dotnet/core/whats-new/dotnet-10/runtime

Inlining improvements

Various inlining improvements have been made in .NET 10.

The JIT can now inline methods that become eligible for devirtualization due to previous inlining. This improvement allows the JIT to uncover more optimization opportunities, such as further inlining and devirtualization.

...

Return types

During inlining, the JIT now updates the type of temporary variables that hold return values. If all return sites in a callee yield the same type, this precise type information is used to devirtualize subsequent calls. This enhancement complements the improvements in late devirtualization and array enumeration de-abstraction.

[coveralls]

coverage: 99.066% (-0.04%) from 99.11% — users/alexpeck/inline10 into main