On Sat, 3 Aug 2019, Aaron wrote: > I am afraid LTO or other upcoming methods of code-improvementwill bring grief > on us. > Why should someone want do write such code? Answer: speed > > Unfortunately, it is not valid C due to the effective type rules. (6.5 > Expression 7). You are correct that such code is invalid and can be observably broken with LTO. GCC supports the 'may_alias' type attribute to aid in writing such code. You can refer to documentation at https://gcc.gnu.org/onlinedocs/gcc/Common-Type-Attributes.html and see how musl libc uses it in implementations of string functions: (e.g. strlen) http://git.musl-libc.org/cgit/musl/tree/src/string/strlen.c?id=4d0a82170a25464c39522d7190b9fe302045ddb2 (e.g. memmove) http://git.musl-libc.org/cgit/musl/tree/src/string/memmove.c?id=4d0a82170a25464c39522d7190b9fe302045ddb2 (same for C++) HTH. Alexander
