[Bug]: Constexpr expansion compilation error with GCC's UndefinedBehaviorSanitizer
Author: kaxubCreated Mar 6, 2024Updated Sep 1, 2026
Describe the issue
When building abseil with GCC with -fsanitize=undefined, the following compilation error occurs:
/abseil/absl/container/internal/raw_hash_set.h:3364:56: in 'constexpr' expansion of 'absl::container_internal::hash_policy_traits<absl::container_internal::FlatHashMapPolicy<std::basic_string_view<char>, absl::CommandLineFlag*>, void>::get_hash_slot_fn<absl::container_internal::StringHash>()'
/abseil/absl/container/internal/hash_policy_traits.h:163:54: error: '(absl::container_internal::TypeErasedApplyToSlotFn<absl::container_internal::StringHash, std::basic_string_view<char> > == 0)' is not a constant expression
163 | return Policy::template get_hash_slot_fn<Hash>() == nullptr
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~
make-4.3[4]: *** [absl/flags/CMakeFiles/flags_reflection.dir/build.make:66: absl/flags/CMakeFiles/flags_reflection.dir/reflection.cc.o] Error 1 This code producing the error has been introduced with commit 4c7e7c7d9.
The error does not occur when building with no sanitizer or when building with -fsanitize=address or -fsanitize=thread.
This seems to be a known GCC bug: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71962
Steps to reproduce the problem
git clone https://github.com/abseil/abseil-cpp.git
cd abseil-cpp
mkdir build
cd build
cmake -DCMAKE_CXX_FLAGS="-fsanitize=undefined" ..
makeIsolated expression from the method where the error occurs (absl::container_internal::hash_policy_traits::get_hash_slot_fn<Hash>()) with -std=gnu++17 -fsanitize=undefined: https://godbolt.org/z/8bEazf6e5
What version of Abseil are you using?
7bd9ff910d489658da58251de1317eb3f790a2c6
What operating system and version are you using?
Ubuntu 20.04.6 LTS
What compiler and version are you using?
GCC 9.4.0 Also tested with GCC 13.2 on linked godbolt.
What build system are you using?
cmake 3.16.3
Additional context
No response
Source: abseil/abseil-cpp