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This is related to #27987 and #20064 and perhaps the pymalloc patch
from #18835.
I think PyMem_Malloc() should guarantee alignof(max_align_t).
It actually did before the "#define PYMEM_FUNCS PYOBJ_FUNCS" optimization,
so we have a sort of regression here.

> I think PyMem_Malloc() should guarantee alignof(max_align_t).
Do you mean the C++ std::max_align_t? Does C99 have something like that?
The Linux malloc() manual page says:
"The malloc() and calloc() functions return a pointer to the allocated memory, which is suitably aligned for any built-in type."
But I don't know the list of C built-in types.

> Do you mean the C++ std::max_align_t? Does C99 have something like that?
> 
> The Linux malloc() manual page says:
> 
> "The malloc() and calloc() functions return a pointer to the allocated memory, which is suitably aligned for any built-in type."
C11 has max_align_t, but also for C99 "any builtin type" means 16 byte alignment
for long double on x64, so malloc() and calloc() are required to align 16 bytes
with -std=c99 (and earlier).
max_align_t is just a shorthand to express the concept.

max_align_t is a bit of a kitchen sink and will specify larger and larger alignment in the future, e.g. 32-byte alignment for a complex _Float128 type (a pair of two _Float128 variables). The alignment is also not generally useful for allocations whose size is smaller than the alignment. (Many mallocs do not follow the C standard and do not provide 16-byte alignment when 8 bytes are allocated, although alignof(max_align_t) is 16.)