Demonstrate the problem that using blackhole is quite tricky

blackhole_problems_py.py

try:
    import pypyjit
except ImportError:
    def blackbox(x):
        return x
else:
    def identity(x):
        return x

    def blackbox(x):
        return pypyjit.residual_call(identity, x)

def main():
    import time

    t1 = time.perf_counter()
    for i in range(10_000_000):
        pass
    t2 = time.perf_counter()
    print("empty loop", t2 - t1)


    t1 = time.perf_counter()
    for i in range(10_000_000):
        blackbox(1)
    t2 = time.perf_counter()
    print("empty loop with blackbox call", t2 - t1)

    t1 = time.perf_counter()
    for i in range(10_000_000):
        l = "abcdefghi"
        l.index("ghi") # constant-folded
    t2 = time.perf_counter()
    print("constant-folded", t2 - t1)

    t1 = time.perf_counter()
    substring = blackbox("ghi")
    for i in range(10_000_000):
        l = "abcdefghi"
        l.index(substring) # can't constant-fold, but it's loop invariant
    t2 = time.perf_counter()
    print("loop-invariant, despite blackbox", t2 - t1)

    t1 = time.perf_counter()
    substring = "ghi"
    for i in range(10_000_000):
        l = "abcdefghi"
        l.index(blackbox(substring)) # completely unrealistic overhead due to calling blackbox
    t2 = time.perf_counter()
    print("no cheating, but distorted", t2 - t1)

main()

# my laptop, pypy3.10:
# empty loop 0.005483658984303474
# empty loop with blackbox call 0.7468732330016792
# constant-folded 0.004697702941484749
# loop-invariant, despite blackbox 0.09397784899920225
# no cheating, but distorted 0.8346890190150589

# python3.11
# empty loop 0.07850259297993034
# empty loop with blackbox call 0.23288042598869652
# constant-folded 0.4955052570439875
# loop-invariant, despite blackbox 0.5159864641027525
# no cheating, but distorted 0.6361238369718194