[Python-Dev] Optimization targets

"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
     return a-b

f(1.0, 2.0)

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.


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