[flohofwoe]

AFAIK alignment doesn't even matter anymore (for CPU data at least) since the 'word size' of a modern CPU is the size of a cache line (32 or 64 bytes?), e.g. unaligned accesses within a 32 or 64 byte block are not different than aligned accesses.

(technically there is still an advantage of items aligned to their size in that such an item can never straddle adjacent cache lines though)

And there's also still tons of different alignment requirements when working with GPU data - and interestingly those alignment requirements may differ from C's alignment rules, so you may need to explicitly use packed structs (which are still not a standard C feature!) with manual padding.

[birn559]

My understanding is that C++ compilers still add padding by default for performance reasons. CPU will have to spend a few cycles to reorganize data that is not aligned in chunks of 4 bytes.

[flohofwoe]

Daniel Lemire did some measuring ~~recently~~ (oops, in 2012):

https://lemire.me/blog/2012/05/31/data-alignment-for-speed-m...

TL;DR: 10% difference on what in 2012 was a low-end CPU, no difference on "new in 2012" CPUs. So my guess is that by now it really doesn't matter anymore :)

[birn559]

Wasn't aware of that, thanks for the link!

[xxs]

> CPU will have to spend a few cycles to reorganize data that is not aligned in chunks of 4 bytes.

That's not true for quite a lot of CPUs. Pretty much all x64 and stuff don't care