When PGO is not used, compilers don't know which part is hot.

So gcc failed to inline hot code in pymalloc_alloc and pymalloc_free
into _PyObject_Malloc and _PyObject_Free.  For example, only this code is inlined into _PyObject_Malloc.

    if (nbytes == 0) {
        return 0;
    }
    if (nbytes > SMALL_REQUEST_THRESHOLD) {
        return 0;
    }

But the hottest part is taking memory block from freelist in the pool.
To optimize it,

* make pymalloc_alloc and pymalloc_free inline functions
* Split code for rare / slow paths out to new functions

In PR 14674, pymalloc is now as fast as mimalloc in spectral_norm benchmark.

  $ ./python bm_spectral_norm.py --compare-to=./python-master
  python-master: ..................... 199 ms +- 1 ms
  python: ..................... 176 ms +- 1 ms

  Mean +- std dev: [python-master] 199 ms +- 1 ms -> [python] 176 ms +- 1 ms: 1.13x faster (-11%)

New changeset fb26504d14a08fcd61bb92bb989b6d2b12188535 by Inada Naoki in branch 'master':
bpo-37543: optimize pymalloc (#14674)
https://github.com/python/cpython/commit/fb26504d14a08fcd61bb92bb989b6d2b12188535