There’s no single definitive answer to your question. Firstly, the external behavior of a freed block will depend on whether it was released to the system or stored as a free block in the internal memory pool of the process or C runtime library. In modern OSes the memory “returned to the system” will become … Read more
Here are step-by-step instructions for building a Hello World .exe using llvm/clang on Mac OS X. Cross-compile Hello World for Windows using Clang/LLVM on Mac OS X Install llvm with homebrew. This will include the clang and the llvm linker. brew install llvm You’ll need access to Visual Studio C++ libraries and headers, which are … Read more
We don’t want to place the vtable in each translation unit. So there must be some ordering of translation units, such that we can say then, that we place the vtable in the “first” translation unit. If this ordering is undefined, we emit the warning. You find the answer in the Itanium CXX ABI. In … Read more
The C11 standard says this, 6.8.5/6: An iteration statement whose controlling expression is not a constant expression,156) that performs no input/output operations, does not access volatile objects, and performs no synchronization or atomic operations in its body, controlling expression, or (in the case of a for statement) its expression-3, may be assumed by the implementation … Read more
Several of the answers in the question you link talk about rewriting the code to be branchless and thus avoiding any branch prediction issues. That’s what your updated compiler is doing. Specifically, clang++ 10 with -O3 vectorizes the inner loop. See the code on godbolt, lines 36-67 of the assembly. The code is a little … Read more
Foreknowledge: I had same delusion about this: “If llvm is targeting for all backends including riscv, we should be able to compile our codes just giving a clang flag like –target=riscv32, -target riscv64 etc. without doing extra operation” and I had similar question, but it is not like that. Although LLVM supports riscv target, you … Read more
I suspect this issue is because of the two C++ runtime libraries available under OS X. Use the following to link the dynamic library: clang++ -stdlib=libc++ -o Analysis.dylib -shared DataFile.o CR39DataFile.o (the -stdlib=libc++ being the key difference). I think the default C++ runtime is the GNU implementation which is confusing the linker as you compiled … Read more
I believe __STDC_IEC_559__ relies on some library features and can’t be defined solely by the compiler. See this post for some information. This is not uncommon for C — the compiler and the C library must sometimes cooperate in order to implement the entire standard. What you’re asking depends on the compiler. I think you … Read more
Here is a simpler case that triggers the same warning: class A { public: // … A(); }; A my_A; // triggers said warning test.cpp:7:3: warning: declaration requires a global constructor [-Wglobal-constructors] A my_A; // triggers said warning ^~~~ 1 warning generated. This is perfectly legal and safe C++. However for every non-trivial global constructor … Read more
Using C++11, the non-macro form is: char arrname[5]; size_t count = std::extent< decltype( arrname ) >::value; And extent can be found in the type_traits header. Or if you want it to look a bit nicer, wrap it in this: template < typename T, size_t N > size_t countof( T ( & arr )[ N ] … Read more