https://gcc.gnu.org/bugzilla/show_bug.cgi?id=52981
--- Comment #5 from David Stone <david at doublewise dot net> --- After thinking about this some more, we are not answering the question that splitting it into two warnings is really trying to get at. The first, and most important is not "Is there padding in the middle of the structure", but "Can I rearrange my data members to save space?". -Wwasted-space might be a good name for this warning. I believe in all systems that gcc targets*, the optimal size can be achieved by arranging elements largest to smallest, so we could just compare the size of a theoretical struct with that arrangment and the size of the user's struct. The second thing the user might wonder is "Do I have padding that I cannot resolve by rearranging". This warning can alert the user that a small change in the size of their data types (or possibly moving data into different structures) could have a greater-than-expected size savings. This is more like the current -Wpadded. * A strange system with 4-byte, 3-byte, and 1-byte aligned types could have a more efficient representation by following every 3 with a 1. I am unsure if this is actually valid according to the C or C++ standard. As long as all of the systems just have power-of-two alignment, the largest to smallest works.
