Comment by skybrian

These tail-call functions are part of a program’s inner loop. It seems like we shouldn’t expect allocation within an inner loop to be fast? Other than local variables, that is.

In an interpreter, it seems like either you’re allocating outside the interpreter loop (the lifetime is that of the interpreter) or it’s within a particular (slow) instruction, or it’s part of the language being interpreted and the lifetime can’t be handled by RAII. There will be fast instructions that don’t allocate and slower ones that do.

Interpreters are a bit weird in that there are lots of instructions that do almost nothing so the overhead of the loop is significant, combined with having lots of complication inside the loop and little ability to predict what instruction comes next. This is unlike many loops that can be unrolled.