On: Both GCC and Clang generate strange/inefficient code

[rwmj]

The OP should try with -march=native so the compiler can use vector instructions.

Slightly off-topic but I like this way to test if memory is all zeroes: https://rusty.ozlabs.org/2015/10/20/ccanmems-memeqzero-itera... (see "epiphany #2" at the bottom of the page) I really wish there was a standard libc function for it.

[rsf → rwmj]

> The OP should try with -march=native so the compiler can use vector instructions.

I just tried "-O3 -march=znver5" as well as "-O3 -march=native" and it didn't seem to make any difference.