> In 3.8, the union used to ensure alignment on a C double is gone.
Note that two uintptr_t is aligned 16bytes on 64bit platforms and 8bytes on 32bit platforms.
Python 3.7 is worse than 3.8.
It used "double dummy" to align by 8 bytes, not 16 bytes.
We should use "long double" to align by 16 bytes.
https://software.intel.com/sites/default/files/article/402129/mpx-linux64-abi.pdf
But it means +8 bytes for all tuples. If we backport PR-12850 to 3.7, +8 bytes for 1/2 tuples, and +16 bytes for remaining tuples.
Any ideas about reduce impact for Python 3.7?
For example, can we add 8byte dummy to PyGC_Head, and tuple use the dummy for hash? Maybe, it breaks ABI.... Not a chance...
I wonder if we can add -fmax-type-align=8 for extension types...