Re: [PATCH] PPC JIT failure for t/pmc/threads_8.pasm

Jeff Clites <jclites@xxxxxxx> wrote:
> I was getting a failure under JIT on PPC for t/pmc/threads_8.pasm, and
> the problem turned out to be that emitting a restart op takes 26
> instructions, or 104 bytes, and we were hitting the grow-the-arena
> logic just shy of what would have triggered a resize, then running off
> the end.

Duh. It's probably time to generate a JITted restart function.

> The below patch fixes this; really that magic number (200, now) needs
> to be bigger than the amount of space we'd ever need to emit the JIT
> code for a single op (plus saving registers and such), but with the
> possibility of dynamically loadable op libs (with JIT?),

Not easily. Or it would be not too hard. Given a fairly complete
implementation of core.jit, we have a function table (per platform) that
has slots for every processor instruction (or almost: Parrot hasn't yet
vector opcodes). So a new opcode could be written in terms of existing
opcodes, which would easily allow the generation of JITted variants.

If a new opcode is too complex, it could be written (partly) in C, which
would need just one new JIT opcode call_c_func. And that is exactly what
Parrot_jit_build_call_func on i386 is already doing.

> ... it's hard to
> say what number is guaranteed to be large enough.

If we ever have loadable JIT code, will have an interface to set that
magic number.

Thanks, applied.

> JEff

leo