The Performance Impact of C++'s `final` Keyword

1. Roslyn

   1 166 19,370 10.0 C#

   The Roslyn .NET compiler provides C# and Visual Basic languages with rich code analysis APIs.

   

   .NET is a little smarter about switch code generation these days: https://github.com/dotnet/roslyn/pull/66081

2. CodeRabbit

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3. styx

   2 11 - -

   > I'd love to see the codegen differences between the applications

   There are two applications, dynamic calls and dynamic casts.

   Dynamic casts to final classes dont require to check the whole inheritance chain. Recently done this in styx [0]. The gain may appear marginal, e.g 3 or 4 dereferences saved but in programs based on OOP you can easily have *Billions* of dynamic casts saved.

   [0]: https://gitlab.com/styx-lang/styx/-/commit/62c48e004d5485d4f....

4. CoreCLR

   3 22 12,786 0.0

   Discontinued CoreCLR is the runtime for .NET Core. It includes the garbage collector, JIT compiler, primitive data types and low-level classes.

   

   Yes, that is true. I'm not sure about JVM implementation details but the reason the comment says "virtual and interface" calls is to outline the difference. Virtual calls in .NET are sufficiently close[0] to virtual calls in C++. Interface calls, however, are coded differently[1].

   Also you are correct - virtual calls are not terribly expensive, but they encroach on ever limited* CPU resources like indirect jump and load predictors and, as noted in parent comments, block inlining, which is highly undesirable for small and frequently called methods, particularly when they are in a loop.

   * through great effort of our industry to take back whatever performance wins each generation brings with even more abstractions that fail to improve our productivity

   [0] https://github.com/dotnet/coreclr/blob/4895a06c/src/vm/amd64...

   [1] https://github.com/dotnet/runtime/blob/main/docs/design/core... (mind you, the text was initially written 18 ago, wow)

5. .NET Runtime

   4 677 16,002 10.0 C#

   .NET is a cross-platform runtime for cloud, mobile, desktop, and IoT apps.

   

   Yes, that is true. I'm not sure about JVM implementation details but the reason the comment says "virtual and interface" calls is to outline the difference. Virtual calls in .NET are sufficiently close[0] to virtual calls in C++. Interface calls, however, are coded differently[1].

   Also you are correct - virtual calls are not terribly expensive, but they encroach on ever limited* CPU resources like indirect jump and load predictors and, as noted in parent comments, block inlining, which is highly undesirable for small and frequently called methods, particularly when they are in a loop.

   * through great effort of our industry to take back whatever performance wins each generation brings with even more abstractions that fail to improve our productivity

   [0] https://github.com/dotnet/coreclr/blob/4895a06c/src/vm/amd64...

   [1] https://github.com/dotnet/runtime/blob/main/docs/design/core... (mind you, the text was initially written 18 ago, wow)

6. preprocessor

   5 2 101 3.7 C++

   Boost.org preprocessor module

   

7. PSRayTracing

   6 1 - -

   (I am the author of the issue)

   [1] https://gitlab.com/define-private-public/PSRayTracing/-/issu...

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