[Python-Dev] Optimization targets (original) (raw)

"Martin v. Löwis" martin at v.loewis.de
Thu Apr 15 15:07:12 EDT 2004

Jeremy Hylton wrote:

Another question that I'd love to hear the answer to: What's the difference between Pysco and something like this Self implementation or the HotSpot Java implementation?

Psyco is specializing, and that is the main difference compared to Java Hotspot. If you have a program

def f(a, b): if a>b: return a else: return a-b

f(1,2) f(1.0, 2.0) f([1,2],[3,4])

then psyco generates machine code for three functions

int f_int(int a, int b){ // uses process int arithmethic throughout if(a>b)return a; else return a-b; }

double f_double(double a, double b){ // uses FPU ops throughout if(a>b)return a; else return a-b; }

list f_list(list a, list b){ // might invoke C functions if(list_gt(a, b))return a; else raise TypeError("unexpected operands"); }

(it actually generates different specializations)

In Hotspot, the type of f would already be defined in the Java source code, and Hotspot generates native machine instructions for it.

The changes over standard JIT appear to be inlining; it also appears to do inlining of virtual functions, combined with a type check to detect cases where the a different functions should have been called compared to the last time the virtual call was made.

Regards, Martin

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