> From: M.-A. Lemburg [mailto:mal@lemburg.com]
>
> Back in the 1.5.2 days I played a lot with the ceval loop and
> the best results I got came from:
>
> a) moving the LOAD_FAST opcode out of the switch
Are you suggesting a test for LOAD_FAST before the switch,
e.g.
if (opcode == LOAD_FAST) {
// load fast
}
else switch (opcode) {
// body
}
> b) splitting the switch statement in two: the first one for
> more commonly used opcodes, the second one for less often
> used opcodes
Are you suggesting something like:
switch (opcode) {
case COMMON_OP:
case COMMON_OP:
...
default:
switch (opcode) {
case UNCOMMON_OP:
case UNCOMMON_OP:
}
Or something like this:
switch (opcode) {
case COMMON_OP:
case COMMON_OP:
...
default:
handle_uncommon_ops();
}
> c) ordering cases in the switch statements by usage frequency
> (using average opcode usage frequencs obtained by
> instrumenting the interpreter)
I might try a little simulated annealing to generate layouts with high
frequency opcodes near the front and coorcurring opcodes near each
other.
> The last point is probably compiler dependent. GCC has the
> tendency to use the same layout for the assembler code as you
> use in the C source code, so placing often used code close to
> the top results in better locality (at least on my machines).
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