Avoid delegate allocation in generic cycle detector #79842
Merged
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Removes 1,000,000 (one million) allocations while compiling a hello world. We were allocating a delegate and a closure each time we saw a reference from something generic to something generic.
This replaces the delegate with a manual closure allocated on the stack. The number of stack allocated entries was chosen arbitrarily. The highest recursion we see in CoreLib is for 3 elements, so 4 includes a bit of a buffer.
Maybe it's a tiny bit less readable, but not that much.
Cc @dotnet/ilc-contrib