I ran a coarse benchmark on the debug mode using PR 10669: I ran the full Python test suite.
=> I don't see any significant impact on performance.
* C macros: PR 10669
* static inline functions: commit 3bb183d7fb83ad6a84ec13dea90f95d67be35c69 (PR 10669 parent)
git clean -fdx # remove *all* untracked files
./configure --with-pydebug && make
./python -m test -j0 -r --randseed=2411717
Result:
* C macros: 3 min 22 sec
* static inline functions: 3 min 26 sec (+4 sec, +2%)
I used my laptop to run the benchmark: Fedora 29 with GCC 8.2.1. I was still using the laptop to run other tasks.