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
```
