On Thu, Jan 21, 2010 at 3:14 PM, Collin Winter <collinwin...@google.com> wrote: >> P.S. Is there any chance of LLVM doing something like tracing JITs? >> Those seem somewhat more promising to me (even though I understand >> they're quite hard in the face of Python features like stack frames). > > Yes, you could implement a tracing JIT with LLVM. We chose a > function-at-a-time JIT because it would a) be an easy-to-implement > baseline to measure future improvement, and b) create much of the > infrastructure for a future tracing JIT. Implementing a tracing JIT > that crosses the C/Python boundary would be interesting.
I was thinking about this recently. I think it would be a good 3 month project for someone. Basically, we could turn off feedback recording until we decide to start a trace at a loop header, at which point we switch to recording everything, and compile the trace into a single stream of IR with a bunch of guards and side exits. The side exits could be indirect tail calls to either a side exit handler, or a freshly compiled trace starting at the opcode where the side exit occurred. The default handler would switch back to the interpreter, record the trace, kick off compilation, and patch the indirect tail call target. The only limitation with that approach is that you would have to do extra work to propagate conditions like passed guards across the call boundary, since we currently try to throw away as much LLVM IR as possible after compilation to save memory. So yes, I think it would be possible to implement a tracing JIT in the future. If people are really interested in that, I think the best way to get there is to land unladen in py3k as described in the PEP and do more perf work like this there and in branches on python.org, where it can be supported by the wider Python developer community. Reid _______________________________________________ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
