https://gcc.gnu.org/bugzilla/show_bug.cgi?id=120891
Bug ID: 120891 Summary: [C++20] ICE in tsubst when processing nested template lambda and with in template instantiation Product: gcc Version: 16.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c++ Assignee: unassigned at gcc dot gnu.org Reporter: marko1616 at outlook dot com Target Milestone: --- Created attachment 61765 --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=61765&action=edit Reproduction code Abstract: Encounters an internal compiler error when processing nested lambda expressions involving tuple operations within template instantiation. Tested version: GNU C++17 (Debian 14.2.0-19) and mainline(92cbe07) Output: ``` Using built-in specs. COLLECT_GCC=/opt/compiler-explorer/gcc-snapshot/bin/g++ Target: x86_64-linux-gnu Configured with: ../gcc-trunk-20250630/configure --prefix=/opt/compiler-explorer/gcc-build/staging --enable-libstdcxx-backtrace=yes --build=x86_64-linux-gnu --host=x86_64-linux-gnu --target=x86_64-linux-gnu --disable-bootstrap --enable-multiarch --with-abi=m64 --with-multilib-list=m32,m64,mx32 --enable-multilib --enable-clocale=gnu --enable-languages=c,c++,fortran,ada,objc,obj-c++,go,d,rust,m2,cobol --enable-ld=yes --enable-gold=yes --enable-libstdcxx-debug --enable-libstdcxx-time=yes --enable-linker-build-id --enable-lto --enable-plugins --enable-threads=posix --with-pkgversion=Compiler-Explorer-Build-gcc-92cbe073528f774361519a430c2c0df859fe1329-binutils-2.44 Thread model: posix Supported LTO compression algorithms: zlib gcc version 16.0.0 20250630 (experimental) (Compiler-Explorer-Build-gcc-92cbe073528f774361519a430c2c0df859fe1329-binutils-2.44) COLLECT_GCC_OPTIONS='-fdiagnostics-color=always' '-g' '-o' '/app/output.s' '-fno-verbose-asm' '-S' '-v' '-std=c++20' '-shared-libgcc' '-mtune=generic' '-march=x86-64' '-dumpdir' '/app/' /opt/compiler-explorer/gcc-trunk-20250630/bin/../libexec/gcc/x86_64-linux-gnu/16.0.0/cc1plus -quiet -v -imultiarch x86_64-linux-gnu -iprefix /opt/compiler-explorer/gcc-trunk-20250630/bin/../lib/gcc/x86_64-linux-gnu/16.0.0/ -D_GNU_SOURCE <source> -quiet -dumpdir /app/ -dumpbase output.cpp -dumpbase-ext .cpp -mtune=generic -march=x86-64 -g -std=c++20 -version -fdiagnostics-color=always -fno-verbose-asm -o /app/output.s GNU C++20 (Compiler-Explorer-Build-gcc-92cbe073528f774361519a430c2c0df859fe1329-binutils-2.44) version 16.0.0 20250630 (experimental) (x86_64-linux-gnu) compiled by GNU C version 11.4.0, GMP version 6.2.1, MPFR version 4.1.0, MPC version 1.2.1, isl version isl-0.24-GMP GGC heuristics: --param ggc-min-expand=30 --param ggc-min-heapsize=4096 ignoring nonexistent directory "/opt/compiler-explorer/gcc-trunk-20250630/bin/../lib/gcc/x86_64-linux-gnu/16.0.0/../../../../x86_64-linux-gnu/include" ignoring duplicate directory "/opt/compiler-explorer/gcc-trunk-20250630/bin/../lib/gcc/../../lib/gcc/x86_64-linux-gnu/16.0.0/../../../../include/c++/16.0.0" ignoring duplicate directory "/opt/compiler-explorer/gcc-trunk-20250630/bin/../lib/gcc/../../lib/gcc/x86_64-linux-gnu/16.0.0/../../../../include/c++/16.0.0/x86_64-linux-gnu" ignoring duplicate directory "/opt/compiler-explorer/gcc-trunk-20250630/bin/../lib/gcc/../../lib/gcc/x86_64-linux-gnu/16.0.0/../../../../include/c++/16.0.0/backward" ignoring duplicate directory "/opt/compiler-explorer/gcc-trunk-20250630/bin/../lib/gcc/../../lib/gcc/x86_64-linux-gnu/16.0.0/include" ignoring nonexistent directory "/usr/local/include/x86_64-linux-gnu" ignoring duplicate directory "/opt/compiler-explorer/gcc-trunk-20250630/bin/../lib/gcc/../../lib/gcc/x86_64-linux-gnu/16.0.0/include-fixed/x86_64-linux-gnu" ignoring duplicate directory "/opt/compiler-explorer/gcc-trunk-20250630/bin/../lib/gcc/../../lib/gcc/x86_64-linux-gnu/16.0.0/include-fixed" ignoring nonexistent directory "/opt/compiler-explorer/gcc-trunk-20250630/bin/../lib/gcc/../../lib/gcc/x86_64-linux-gnu/16.0.0/../../../../x86_64-linux-gnu/include" #include "..." search starts here: #include <...> search starts here: /opt/compiler-explorer/gcc-trunk-20250630/bin/../lib/gcc/x86_64-linux-gnu/16.0.0/../../../../include/c++/16.0.0 /opt/compiler-explorer/gcc-trunk-20250630/bin/../lib/gcc/x86_64-linux-gnu/16.0.0/../../../../include/c++/16.0.0/x86_64-linux-gnu /opt/compiler-explorer/gcc-trunk-20250630/bin/../lib/gcc/x86_64-linux-gnu/16.0.0/../../../../include/c++/16.0.0/backward /opt/compiler-explorer/gcc-trunk-20250630/bin/../lib/gcc/x86_64-linux-gnu/16.0.0/include /opt/compiler-explorer/gcc-trunk-20250630/bin/../lib/gcc/x86_64-linux-gnu/16.0.0/include-fixed/x86_64-linux-gnu /opt/compiler-explorer/gcc-trunk-20250630/bin/../lib/gcc/x86_64-linux-gnu/16.0.0/include-fixed /usr/local/include /opt/compiler-explorer/gcc-trunk-20250630/bin/../lib/gcc/../../include /usr/include/x86_64-linux-gnu /usr/include End of search list. Compiler executable checksum: 7cf76c5f6d00c279175354f3ebdbf134 <source>: In instantiation of 'trigger_ice<Foo>()::<lambda(std::index_sequence<_Inds ...>)> [with long unsigned int ...Is = {0}; std::index_sequence<_Inds ...> = std::integer_sequence<long unsigned int, 0>]': <source>:19:6: required from 'void trigger_ice() [with T = Foo]' 15 | [&]<size_t... Is>(std::index_sequence<Is...>) { | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 16 | (([&]() { | ~~~~~~~~~ 17 | using qux = decltype(std::get<Is>(tuple)); | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 18 | })(), ...); | ~~~~~~~~~~~ 19 | }(std::make_index_sequence<std::tuple_size_v<decltype(tuple)>>{}); | ~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ <source>:23:21: required from here 23 | trigger_ice<Foo>(); | ~~~~~~~~~~~~~~~~^~ <source>:14:10: internal compiler error: in tsubst, at cp/pt.cc:16787 14 | auto tuple = baz.as_tuple(); | ^~~~~ 0x2844425 diagnostic_context::diagnostic_impl(rich_location*, diagnostic_metadata const*, diagnostic_option_id, char const*, __va_list_tag (*) [1], diagnostic_t) ???:0 0x2866fc6 internal_error(char const*, ...) ???:0 0xaede72 fancy_abort(char const*, int, char const*) ???:0 0xd4bb3d tsubst(tree_node*, tree_node*, int, tree_node*) ???:0 0xd4c0c4 tsubst(tree_node*, tree_node*, int, tree_node*) ???:0 0xd67f75 tsubst_lambda_expr(tree_node*, tree_node*, int, tree_node*) ???:0 0xd61894 tsubst_pack_expansion(tree_node*, tree_node*, int, tree_node*) ???:0 0xd6e87d instantiate_decl(tree_node*, bool, bool) ???:0 0xbf7843 maybe_instantiate_decl(tree_node*) ???:0 0xbf95b7 mark_used(tree_node*, int) ???:0 0xb2a403 build_op_call(tree_node*, vec<tree_node*, va_gc, vl_embed>**, int) ???:0 0xd98c6e finish_call_expr(tree_node*, vec<tree_node*, va_gc, vl_embed>**, bool, bool, int) ???:0 0xd6e87d instantiate_decl(tree_node*, bool, bool) ???:0 0xd7de82 instantiate_pending_templates(int) ???:0 0xbfd5d1 c_parse_final_cleanups() ???:0 0xe7e498 c_common_parse_file() ???:0 Please submit a full bug report, with preprocessed source (by using -freport-bug). Please include the complete backtrace with any bug report. See <https://gcc.gnu.org/bugs/> for instructions. Compiler returned: 1 ```