Prevent devirtualization into unallocated types #73839
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If we were in a situation like in the regression test, we would devirtualize the `GrabObject` call to `SomeUnallocatedClass.GrabObject`. But because `SomeUnallocatedClass` was never allocated, the scanner didn't scan it, and bad things would happen. Prevent devirtualizing into types that were not seen as allocated. This is not a real issue for non-generic (non-shareable) types because the tentative instance method optimization generates throwing bodies for these. But tentative method optimization doesn't run for shared generics: https://github.com/dotnet/runtime/blob/4cbe6f99d23e04c56a89251d49de1b0f14000427/src/coreclr/tools/Common/Compiler/MethodExtensions.cs#L115 This was rare enough that we haven't seen it until I did dotnet#73683 and there was one useless constructor that we stopped generating and triggered this. This also includes what is essentially a rollback of dotnet/runtimelab#1700. This should have been rolled back with dotnet#66145 but I forgot we had this. It was not needed.
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If we were in a situation like in the regression test, we would devirtualize the
GrabObjectcall toSomeUnallocatedClass.GrabObject. But becauseSomeUnallocatedClasswas never allocated, the scanner didn't scan it, and bad things would happen.Prevent devirtualizing into types that were not seen as allocated.
This is not a real issue for non-generic (non-shareable) types because the tentative instance method optimization generates throwing bodies for these. But tentative method optimization doesn't run for shared generics:
runtime/src/coreclr/tools/Common/Compiler/MethodExtensions.cs
Line 115 in 4cbe6f9
This was rare enough that we haven't seen it until I did #73683 and there was one useless constructor that we stopped generating and triggered this.
This also includes what is essentially a rollback of dotnet/runtimelab#1700. This should have been rolled back with #66145 but I forgot we had this. It was not needed.