PR11926 (closed) tried to allocate SRE_REPEAT on state's stack.
It's feasible, but messes up the code in sre_lib.h, and reduces performance a little (roughly 6% slower), so I gave up this solution.

PR12160 uses a memory pool, this solution doesn't mess up the code.

🔸For infrequent alloc/free scenes, it adds a small overhead:

s = 'a'
p = re.compile(r'(a)?')
p.match(s)  # <- measure this statement

before patch: 316 ns  +- 19 ns
after patch:  324 ns  +- 11 ns, 2.5% slower.
(by perf module)

🔸For very frequent alloc/free scenes, it brings a speedup:

s = 200_000_000 * 'a'
p = re.compile(r'.*?(?:bb)+')
p.match(s)  # <- measure this statement

before patch: 7.16 sec
after patch:  5.82 sec, 18.7% faster.
(best of 10 tests)

🔸I tested in a real case that use 17 patterns to process 100MB data:

before patch: 27.09 sec
after patch:  26.78 sec, 1.1% faster.
(best of 4 tests)