Enable `-fstrict-overflow`

At the moment we compile releases with -fwrapv which makes the code a bit safer, but disables certain optimizations. From the GCC docs:

This option instructs the compiler to assume that signed arithmetic overflow of addition, subtraction and multiplication wraps around using twos-complement representation. This flag enables some optimizations and disables others.

My experiments with running sanitisers seem to suggest that we are nearly already ready for -fno-wrapv (or -fstrict-overflow in general). Doing so could lead to quite a few speedups, but we would need to be more careful with the code we write.

It might be worthwhile to get a few benchmarks.

(To be extra precise, we give -fwrapv for clang and gcc for any build that doesn't get --with-pydebug.)

Pitch

My plan right now is to adapt the build system so that only the modules that need it are build with -fwrapv, and the rest can be build with -fstrict-overflow.

We already have config machinery that can add specific CFLAGS for specific modules only.

Perhaps the whole thing can be gated behind a configure flag, like --with-strict-overflow.

If everything goes well, and this improves performance we can consider adding this functionality to one of the standard optimization options.

We can also work on making more modules -fstrict-overflow safe.

Previous discussion

@markshannon @ericsnowcurrently

Brought up on https://github.com/faster-cpython/ideas/issues/458 and inspired by https://github.com/python/cpython/issues/96678

Some previous issues around -fwrapv:

• https://bugs.python.org/issue11149
• https://bugs.python.org/issue1621
• https://bugs.python.org/issue1608

I'm sure there are more.

Progress so far

As far as is currently known, the three remaining modules that rely on defined integer overflow are fixed by:

• _struct: https://github.com/python/cpython/pull/96739
• audioop: https://github.com/python/cpython/pull/96923
• _ctypes: https://github.com/python/cpython/pull/96925

Linked PRs

• gh-96823
• gh-139595

Bắt đầu với cơ chế cấu hình của hệ thống build bổ sung CFLAGS dành riêng cho từng module, sau đó xem xét công việc được liên kết trong gh-96823 và gh-139595. Thay đổi được đề xuất là một bản build strict-overflow được kiểm soát bằng configure cho các module đủ điều kiện, trong đó các module còn lại phụ thuộc vào overflow được xử lý an toàn và hiệu năng được kiểm tra bằng benchmark.