[Bug c++/59898] alignment problems in std::map with avx/avx2
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59898 --- Comment #5 from ignat at gmx dot net --- 16 overloadable memory allocation functions??? brave new world! Nothing against the possibility to have explicit alignment (when you need to align to a cache line, page or disk-block), but why not just do the right thing and let new return properly aligned pointers by default as it's supposed to do? Isn't that the idea of using a typed language in the first place? Unless I have missed something, I thought the whole point of introducing the alignof operator is exactly to make this possible for user defined allocators. And of course nothing has ever prevented the builtin new to return properly aligned pointers as the compiler internally always has this info. Just because a standard allows to return misaligned pointers to users doesn't mean the implementation has to. ignatius
[Bug c++/59898] alignment problems in std::map with avx/avx2
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59898 --- Comment #2 from ignat at gmx dot net --- (In reply to Jakub Jelinek from comment #1) User error. The standard allocators don't guarantee sufficient alignment for the vector types. OMG, I see. Thx for clarifying. So this means that C++ is incapable of keeping track of the alignment requirements for its types for dynamic allocation and I so far merely got lucky with SSE as malloc happens to return 16-byte aligned pointers on 64-bit Linux. :-( Now that I know what to look for, I see ad-hoc fixes for this design flaw, ehm, feature all over the place. Oh well, yet another stupid incantation to get things to work ... thx ignatius
[Bug c++/59898] alignment problems in std::map with avx/avx2
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59898 --- Comment #3 from Jakub Jelinek jakub at gcc dot gnu.org --- This unfortunately needs to be changed in the C++ standard, as long as the operator new functions/methods that must be used and user can override with their versions don't take the alignment as some parameter, there is no way to find the alignment info and call say posix_memalign or memalign instead of malloc under the hood. And, increasing the guaranteed alignment of malloc or even just operator new unconditionally to the highest possible alignment of any vector (right now 64-bytes for Skylake) would waste lots of memory for the common case of programs that don't really need it.
[Bug c++/59898] alignment problems in std::map with avx/avx2
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59898 --- Comment #4 from Marc Glisse glisse at gcc dot gnu.org --- Here is a link to what the future (C++17) might look like for alignment: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2012/n3396.htm
[Bug c++/59898] alignment problems in std::map with avx/avx2
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59898 Jakub Jelinek jakub at gcc dot gnu.org changed: What|Removed |Added Status|UNCONFIRMED |RESOLVED CC||jakub at gcc dot gnu.org Resolution|--- |INVALID --- Comment #1 from Jakub Jelinek jakub at gcc dot gnu.org --- User error. The standard allocators don't guarantee sufficient alignment for the vector types.
