[rapidlua]

I’ve opened an issue in LLVM bugzilla concerning jump not being folded with address computation on x86 with a proposed fix. Would love if it gets some attention. https://bugs.llvm.org/show_bug.cgi?id=50042

Also been working on a C language extension to enable guaranteed tail calls along with explicit control over registers used for argument passing. Provided that callee-save registers are used for arguments, calling fallback functions incurs no overhead.

https://github.com/rapidlua/barebone-c

[haberman]

Barebone C looks really interesting! I wonder if the same gains could be achieved in a more architecture-independent way by simply introducing a new calling convention where parameters are passed in the registers that are normally callee-save.

This would let the fast path functions use all registers without needing to preserve any of them. It would also let them call fallback functions that use a normal calling convention without needing to spill the parameters to the stack.

[rapidlua]

Thank you for the feedback! A new calling convention could probably nail it for many use cases. Sometimes you want something very special though. E.g. LuaJIT pre-decodes instruction prior to dispatch to squeeze some work into branch misprediction delay. There are limited callee save registers available hence it is better to use volatile registers for instruction arguments. It should be possible to reuse the implementation on different architectures and only tweak the register assignment.