search for: alignas

Is there a way to set the alignment of structure types and/or their members? I noticed that if I use the alignas keyword in c++ that clang introduces a bunch of [Y x i8] style padding. -- edA-qa mort-ora-y Leaf Creator Leaf - the language we always wanted http://leaflang.org/

..."S", file: !5, line: 1, size: 8, align: 8, elements: !7) Am I missing something? What is the purpose of "align: 8" here? Maybe we could include alignment information into DI* objects only when required (and thus dump it only when required): for types with bitfields and when alignas() was specified in code. Please advise. -- Best Regards, Victor

...with the 2 most recent releases of Visual Studio. With the release of VS2019, what do people think of retiring VS2015 support before the next major llvm/clang release? As well as simplifying C++14 migration (admittedly only a little), this should also let us remove a number of hacks (e.g. the alignas/AlignedCharArray hack in AlignOf.h), as well as re-enabling a number of warnings in HandleLLVMOptions.cmake. I haven't noticed any build bots still referring to VS2015 (at least not by name). Simon.

...dard, which is made difficult by the standard being contradictory on many relevant points here. Ultimately I've chosen to be very liberal about what I'm allowing to be considered a newly formed valid pointer. BTW, Richard came up with a wonderful example. What do you make of this?: char alignas(A, B) buffer[max(sizeof(A), sizeof(B))]; A *a = reinterpret_cast<A*>(buffer); B *b = reinterpret_cast<B*>(buffer); new(buffer) A; a->vfn(); new(buffer) B; b->vfn(); Valid? Nick -------------- next part -------------- An HTML attachment was scrubbed... URL: <http:/...

..., file: !5, line: 1, size: 8, align: 8, elements: !7) >> >> Am I missing something? What is the purpose of "align: 8" here? Maybe we could include alignment information into DI* objects only when required (and thus dump it only when required): for types with bitfields and when alignas() was specified in code. > What do you mean by "include" in this context? Are you arguing for making an alignment of 8 the implicit default in textual IR? Or do you want to make DICompositeType variable length? I mean that in this case alignment isn't used anywhere in code further....

...difficult by the standard being contradictory on many relevant points here. Ultimately I've chosen to be very liberal about what I'm allowing to be considered a newly formed valid pointer. > > BTW, Richard came up with a wonderful example. What do you make of this?: > > char alignas(A, B) buffer[max(sizeof(A), sizeof(B))]; > A *a = reinterpret_cast<A*>(buffer); > B *b = reinterpret_cast<B*>(buffer); > new(buffer) A; > a->vfn(); > new(buffer) B; > b->vfn(); > > Valid? > > Nick > > _____________________________...

...er to have much hope of meaningful optimization. And potentially not just across inlining, but through memory — who actually allocates polymorphic values and doesn't use smart pointers these days? > BTW, Richard came up with a wonderful example. What do you make of this?: > > char alignas(A, B) buffer[max(sizeof(A), sizeof(B))]; > A *a = reinterpret_cast<A*>(buffer); > B *b = reinterpret_cast<B*>(buffer); > new(buffer) A; > a->vfn(); > new(buffer) B; > b->vfn(); > > Valid? Let's answer a simpler question. Why is this valid...

...gn: 8, elements: !7) > >>> > >>> Am I missing something? What is the purpose of "align: 8" here? Maybe > we could include alignment information into DI* objects only when required > (and thus dump it only when required): for types with bitfields and when > alignas() was specified in code. > >> What do you mean by "include" in this context? Are you arguing for > making an alignment of 8 the implicit default in textual IR? Or do you want > to make DICompositeType variable length? > > I mean that in this case alignment isn't u...

...or less strict. If all this is true, which testing shows on the x86_64 platform, then I can use zero-sized arrays to force the alignment of any structure element. I don't have to calculate the padding on my own (as does clang). For example, the C++ struct: struct pine { int8_t a; int8_t alignas(int32_t) b; }; Can become: type { i8, [0 x i32], i8 } -- edA-qa mort-ora-y Leaf Creator Leaf - the language we always wanted http://leaflang.org/

On May 9, 2013, at 6:34 PM, Nick Lewycky <nlewycky at google.com> wrote: > I'm looking into how we can improve devirtualization in clang, and there a language in C++ feature I'd like to take advantage of which would let us perform elimination of more vptr loads. In this code: > > Cls *p = new Cls; > p->virtual_method1(); > p->method_changing_vptr(); //

I'm looking into how we can improve devirtualization in clang, and there a language in C++ feature I'd like to take advantage of which would let us perform elimination of more vptr loads. In this code: Cls *p = new Cls; p->virtual_method1(); p->method_changing_vptr(); // uses placement new to legally change the vptr p->virtual_method2(); // invalid! Cls *q = p;

...data<Float>::max_demangled_size] = {0}; + int n = snprintf(num, sizeof(num), float_data<Float>::spec, value); + s += string_ref(num, num + n); + } + } +}; + +template <std::size_t N> +class arena +{ + static const std::size_t alignment = 16; + alignas(alignment) char buf_[N]; + char* ptr_; + + std::size_t + align_up(std::size_t n) noexcept + {return (n + (alignment-1)) & ~(alignment-1);} + + bool + pointer_in_buffer(char* p) noexcept + {return buf_ <= p && p <= buf_ + N;} + +public: + arena() no...