[Python-Dev] Python 3 optimizations... (original) (raw)

Reid Kleckner reid.kleckner at gmail.com
Fri Jul 23 19:19:23 CEST 2010

On Fri, Jul 23, 2010 at 1:58 AM, stefan brunthaler <stefan at brunthaler.net> wrote:

Do I understand correctly that you modify the byte code of modules/functions at runtime?

Yes. Quickening is runtime only optimization technique that rewrites instructions from a generic instruction to an optimized derivative (orignally for the Java virtual machine). It is completely hidden from the compiler and has no other dependencies than the interpreter dispatch routine itself.

How do you generate the specialized opcode implementations? Presumably that is done ahead of time, or you'd have to use a JIT, which is what you're avoiding.

I'm guessing from your comments below about cross-module inlining that you generate a separate .c file with the specialized opcode bodies and then call through to them via a table of function pointers indexed by opcode, but I could be totally wrong. :)

Another benefit of using my technique is that a compiler could decide to inline all of the functions of the optimized derivatives (e.g., the floatadd function call inside my FLOATADD interpreter instruction). Unfortunately, however, gcc currently does not allow for cross-module inlining (AFAIR). (Preliminary tests with manually changing the default inlining size for ceval.c resulted in speedups of up to 1.3 on my machine, so I think inlinling of function bodies for the optimized derivatives would boost performance noticeably.)

There are a variety of solutions to getting cross-module inlining these days. Clang+LLVM support link-time optimization (LTO) via a plugin for gold. GCC has LTO and LIPO as well.

Such an approach would also be very useful for Cython. Think of a profiler that runs a program in CPython and tells you exactly what static type annotations to put where in your Python code to make it compile to a fast binary with Cython. Or, even better, it could just spit out a .pxd file that you drop next to your .py file and that provides the static type information for you.

This would be interesting. We have (obviously) have similar instrumentation in unladen swallow to gather type feedback. We talked with Craig Citro about finding a way to feed that back to Cython for exactly this reason, but we haven't really pursued it.

Reid

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