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To clarify: The situation is still not completely understood? It's not just only the computed gotos, but there is some other regression in Clang19? Basically, the difference between clang19.nocg and clang19 is not really clear?

Btw, what about some clang18.tc comparison, i.e. Clang18 with the new tail-call interpreter? I wonder how that compares to clang19.tc.

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> Btw, what about some clang18.tc comparison

(post author here) Oh, this is something I could have called out explicitly: The tail-calling interpreter relies on a feature (the `preserve_none` calling convention) that only landed in clang-19. That means you can only test it on that version. That coincidence (that 19 added both this feature, and the regression) is part of why this was so easy to miss at first, and why I had to "triangulate" with so many different benchmarks to be confident I understood what was going on.

The article includes a link to the pull request which fixes the regression in LLVM: https://github.com/llvm/llvm-project/pull/114990

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