GeezerVison

Maybe make this macro a one-liner too? It would seem to fit. :-)

For stylistic reasons (consistency with e.g. DISPATCH()) I'd prefer making this a function macro, and moving the semicolon to after the "call". Seeing DISPATCH_GOTO (line 1317) without a semicolon makes my mind do a double-take each time I see it.

Hm, this is disturbing -- tstate (which is pretty much a global structure) now has a pointer to a local variable. That means you have to restore this on every exit from the function. Now, we know there's only one exit, and it's handled there, but it still makes me feel weird. And all this to make it possible to set a single int (perhaps even a single bit) from "outside" this function.

I know, and it would seem like overkill, if it weren't for how critical reads of that single int are.
That one int gets read 100 million times per second, and the code to read it occurs over 100 times in the interpreter.