05dc519011
GCC 15.2 enforces the `DefaultConstructible` requirement for `std::reverse_iterator<llvm::succ_iterator>` causing LLVM to fail to build with C++20 (see https://discourse.llvm.org/t/suspicious-usages-of-std-reverse-iterator-and-associated-llvm-build-failures-with-gcc-15-2-1/89426, issue #182417). ``` $ cmake -G Ninja -S llvm -B llvm/build \ -DCMAKE_INSTALL_PREFIX=$(mktemp -d) \ -DCMAKE_BUILD_TYPE=Release \ -DCMAKE_C_COMPILER=gcc \ -DCMAKE_CXX_COMPILER=g++ \ -DLLVM_ENABLE_PROJECTS="clang;" \ -DLLVM_ENABLE_ASSERTIONS=ON \ -DLLVM_USE_LINKER=lld \ -DCMAKE_CXX_STANDARD=20 \ -DLLVM_OPTIMIZED_TABLEGEN=ON \ -DLLVM_PARALLEL_LINK_JOBS=4 $ ninja -C llvm/build bin/llvm-lib ... /usr/include/c++/15/bits/stl_iterator.h:182:7: error: no matching function for call to ‘llvm::Instruction::succ_iterator::succ_iterator()’ 182 | _GLIBCXX_NOEXCEPT_IF(noexcept(_Iterator())) ... ``` Adding a default constructor fixes this error. Fixes #182417.