Decide on STORE_FAST_LOAD_FAST #160921

"""Compile every .py under LIBDIR with the running interpreter and count opcodes.
Usage: python -I count_opcodes.py LIBDIR"""
import collections, dis, json, os, sys

libdir = sys.argv[1]
CACHE = dis.opmap['CACHE']
counts = collections.Counter()

def walk(co):
    for i in range(0, len(co.co_code), 2):
        op = co.co_code[i]
        if op != CACHE:
            counts[dis.opname[op]] += 1
    for c in co.co_consts:
        if isinstance(c, type(co)):
            walk(c)

for root, dirs, files in os.walk(libdir):
    for f in sorted(files):
        if f.endswith('.py'):
            p = os.path.join(root, f)
            try:
                with open(p, 'rb') as fh:
                    co = compile(fh.read(), p, 'exec')
            except (SyntaxError, ValueError):
                continue
            walk(co)

print(json.dumps({'total': sum(counts.values()), 'counts': counts}, sort_keys=True))

import sys, timeit
lst = list(range(5000))
def ident(it): return [x for x in it]
def plus(it): return [x + 1 for x in it]
def attr(it): return [x.real for x in it]
def rng(n):
    for i in range(n): i
cases = [("[x for x in lst]", lambda: ident(lst)), ("[x + 1 for x in lst]", lambda: plus(lst)),
         ("[x.real for x in lst]", lambda: attr(lst)), ("for i in range(5000): i", lambda: rng(5000))]
print(sys.version.split()[0])
for name, fn in cases:
    best = min(timeit.repeat(fn, number=500, repeat=21)) / 500 * 1e6
    print(f"  {name:28s} {best:7.1f} us")