-fno-strict-aliasing was added in https://github.com/mariadb/server/commit/c192be206ae36398804b473f7b0e4ee4431b71da

Basically it removes some optimizations: https://godbolt.org/z/dzgsVJ

Violating aliasing rules is UB: https://blog.regehr.org/archives/1520

Some cases can be found with UBSAN's check -fsanitize=alignment Something can be caught by compiler itself: https://jira.mariadb.org/browse/MDEV-19386

So instead of violating C/C++ ISO standards and having less optimizations it's better to honour type system an have more optimizations.