Improve performance of dict merges by avoiding incref/decref pairs #158863

"""dict_dict_merge() cases. ctl rows do not run the per-item merge loop:
dense copies take the key-table clone fast path."""
import os
import pyperf

runner = pyperf.Runner()
def S(n): return "{'key%%d' %% i: i for i in range(%d)}" % n

CASES = [
    ("ctl: a + b", "a + b", "a = 1000; b = 2000"),
    ("ctl: dct_100[key]", "d[k]", "d = " + S(100) + "; k = 'key50'"),
    ("ctl: dict(dct_5)  (clone path)", "dict(d)", "d = dict.fromkeys('abcde', 1)"),
    ("ctl: dict(dct_100)  (clone path)", "dict(d)", "d = " + S(100)),

    ("dct.update(dct_5)", "c.update(b)", "b = dict.fromkeys('abcde', 1); c = dict(b)"),
    ("dct.update(dct_100)", "c.update(b)", "b = " + S(100) + "; c = dict(b)"),
    ("dct.update(dct_1000)", "c.update(b)", "b = " + S(1000) + "; c = dict(b)"),
    ("dct.update(dct_100)  (int keys)", "c.update(b)", "b = {i: i for i in range(1000, 1100)}; c = dict(b)"),
    ("dct_100 | other_100", "a | b", "a = " + S(100) + "; b = {'other%d' % i: i for i in range(100)}"),
    ("{**dct_5, **other_5}", "{**a, **b}", "a = dict.fromkeys('abcde', 1); b = dict.fromkeys('fghij', 1)"),
    ("sparse_1000.copy()  (500 deleted)", "d.copy()",
     "d = " + S(1000) + "\nfor i in range(0, 1000, 2): del d['key%d' % i]"),
    ("dict(vars(obj))  (4 attributes)", "dict(v)",
     "class C:\n    def __init__(self): self.a = 1; self.b = 2; self.c = 3; self.d = 4\nv = vars(C())"),
]
for name, stmt, setup in CASES:
    runner.timeit(name, stmt, setup=setup)