llvm/test/tools/llvm-reduce/remove-bbs-sequence.py

import subprocess
import sys

opt = subprocess.run(
    ["opt", "-passes=print<loops>", "-disable-output", sys.argv[1]],
    stdout=subprocess.PIPE,
    stderr=subprocess.PIPE,
)

stdout = opt.stdout.decode()

pattern = "Loop at depth 1 containing"

if pattern in opt.stderr.decode():
    print("This is interesting!")
    sys.exit(0)
else:
    print("This is NOT interesting!")
    sys.exit(1)