https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99861
--- Comment #2 from Alexander Lelyakin <alexander.lelyakin at googlemail dot com> --- There is a shorter sequence: /usr/local/bin/g++ -std=c++20 -fmodules-ts -x c++-system-header stdexcept /usr/local/bin/g++ -std=c++20 -fmodules-ts -x c++-system-header future /usr/local/bin/g++ -std=c++20 -fmodules-ts -x c++-system-header unordered_map /usr/local/bin/g++ -std=c++20 -fmodules-ts -x c++-system-header algorithm ---- hash table checking failed: equal operator returns true for a pair of values with a different hash value In file included from /usr/local/include/c++/11.0.1/vector:66, from /usr/local/include/c++/11.0.1/functional:62, from /usr/local/include/c++/11.0.1/pstl/glue_algorithm_defs.h:13, from /usr/local/include/c++/11.0.1/algorithm:74: /usr/local/include/c++/11.0.1/bits/stl_uninitialized.h: In static member function ‘static _ForwardIterator std::__uninitialized_copy<true>::__uninit_copy(_InputIterator, _InputIterator, _ForwardIterator)’: /usr/local/include/c++/11.0.1/bits/stl_uninitialized.h:110:23: internal compiler error: in hashtab_chk_error, at hash-table.c:137 110 | { return std::copy(__first, __last, __result); } | ^~~~ 0x92db09 hashtab_chk_error() ../../gcc/gcc/hash-table.c:137 0xb3c135 hash_table<spec_hasher, false, xcallocator>::verify(spec_entry* const&, unsigned int) ../../gcc/gcc/hash-table.h:1033 0xb3c6be hash_table<spec_hasher, false, xcallocator>::find_slot_with_hash(spec_entry* const&, unsigned int, insert_option) ../../gcc/gcc/hash-table.h:968 0xaf957b match_mergeable_specialization(bool, spec_entry*) ../../gcc/gcc/cp/pt.c:29908 0xa72a58 trees_in::key_mergeable(int, merge_kind, tree_node*, tree_node*, tree_node*, tree_node*, bool) ../../gcc/gcc/cp/module.cc:10670 0xa76654 trees_in::decl_value() ../../gcc/gcc/cp/module.cc:7903 0xa6f4b7 trees_in::tree_node(bool) ../../gcc/gcc/cp/module.cc:9153 0xa75adb module_state::read_cluster(unsigned int) ../../gcc/gcc/cp/module.cc:14811 0xa75fdd module_state::load_section(unsigned int, binding_slot*) ../../gcc/gcc/cp/module.cc:18082 0xa7609f module_state::lazy_load(unsigned int, binding_slot*) ../../gcc/gcc/cp/module.cc:18740 0xa70320 trees_in::tree_node(bool) ../../gcc/gcc/cp/module.cc:9664 0xa757db module_state::read_cluster(unsigned int) ../../gcc/gcc/cp/module.cc:14717 0xa75fdd module_state::load_section(unsigned int, binding_slot*) ../../gcc/gcc/cp/module.cc:18082 0xa7609f module_state::lazy_load(unsigned int, binding_slot*) ../../gcc/gcc/cp/module.cc:18740 0xa70320 trees_in::tree_node(bool) ../../gcc/gcc/cp/module.cc:9664 0xa757db module_state::read_cluster(unsigned int) ../../gcc/gcc/cp/module.cc:14717 0xa75fdd module_state::load_section(unsigned int, binding_slot*) ../../gcc/gcc/cp/module.cc:18082 0xa7609f module_state::lazy_load(unsigned int, binding_slot*) ../../gcc/gcc/cp/module.cc:18740 0xa70320 trees_in::tree_node(bool) ../../gcc/gcc/cp/module.cc:9664 0xa757db module_state::read_cluster(unsigned int) ../../gcc/gcc/cp/module.cc:14717 Please submit a full bug report, with preprocessed source if appropriate. Please include the complete backtrace with any bug report. See <https://gcc.gnu.org/bugs/> for instructions. ---- g++ (GCC) 11.0.1 20210405 (experimental) Copyright (C) 2021 Free Software Foundation, Inc. This is free software; see the source for copying conditions. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.