https://gcc.gnu.org/bugzilla/show_bug.cgi?id=119938
Bug ID: 119938
Summary: [15/16 Regression][modules] Class type NTTPs are not
considered constant when imported
Product: gcc
Version: 15.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: nshead at gcc dot gnu.org
Blocks: 103524
Target Milestone: ---
There are a large number of issues caused by CNTTPs not properly being
considered constant when imported. Some examples:
===
// eg1.h
struct A { int x; };
template <A a> struct B { static_assert(a.x == 5); };
using C = B<A{5}>;
// eg1.cpp
import "eg1.h";
C c;
$ g++ -std=c++20 -fmodules -S eg1.h eg1.cpp
eg1.cpp:2:3: error: aggregate ‘C c’ has incomplete type and cannot be defined
2 | C c;
| ^
===
// eg2.h
struct A { int x; };
template <A a> void foo() { static_assert(a.x == 5); };
inline void bar() { foo<A{5}>(); }
// eg2.cpp
import "eg2.h";
int main() { bar(); }
$ g++ -std=c++20 -fmodules -S eg2.h eg2.cpp
eg2.cpp:2:21: internal compiler error: Segmentation fault
2 | int main() { bar(); }
| ^
0x3ce0f35 internal_error(char const*, ...)
../../gcc/gcc/diagnostic-global-context.cc:517
0x1d35e92 crash_signal
../../gcc/gcc/toplev.cc:322
0x7f0490a2732f ???
./signal/../sysdeps/unix/sysv/linux/x86_64/libc_sigaction.c:0
0xec9815 tree_check(tree_node const*, char const*, int, char const*, tree_code)
../../gcc/gcc/tree.h:3979
0x158fde8 symbol_table::decl_assembler_name_hash(tree_node const*)
../../gcc/gcc/symtab.cc:84
0x1592d30 symtab_node::get_for_asmname(tree_node const*)
../../gcc/gcc/symtab.cc:1067
0x1592fe1 symtab_node::verify_base()
../../gcc/gcc/symtab.cc:1158
0x15ac085 cgraph_node::verify_node()
../../gcc/gcc/cgraph.cc:3499
0x159394b symtab_node::verify()
../../gcc/gcc/symtab.cc:1362
0x1593d2d symtab_node::verify_symtab_nodes()
../../gcc/gcc/symtab.cc:1482
0x15bdd0e symtab_node::checking_verify_symtab_nodes()
../../gcc/gcc/cgraph.h:702
0x15bd1e7 symbol_table::compile()
../../gcc/gcc/cgraphunit.cc:2332
0x15bd899 symbol_table::finalize_compilation_unit()
../../gcc/gcc/cgraphunit.cc:2607
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.
===
// eg3.h
struct A { int x; };
template <A a> struct B { static constexpr int result = a.x; };
template <int=0> constexpr int foo() { return B<A{5}>::result; };
// eg3.cpp
import "eg3.h";
static_assert(foo() == 5);
$ g++ -std=c++20 -fmodules -S eg3.h eg3.cpp
eg3.cpp:2:21: error: non-constant condition for static assertion
2 | static_assert(foo() == 5);
| ~~~~~~^~~~
In module eg3.h, imported at eg3.cpp:1:
eg3.cpp:2:18: in ‘constexpr’ expansion of ‘foo<>()’
eg3.h:3:56: error: the value of ‘B<A{5}>::result’ is not usable in a constant
expression
3 | template <int=0> constexpr int foo() { return B<A{5}>::result; };
| ~~~~~~~~~^~~~~~
eg3.h:2:48: note: ‘B<A{5}>::result’ used in its own initialiser
2 | template <A a> struct B { static constexpr int result = a; };
^~~~~~
==
... and so forth. This worked correctly in GCC14. I have a patch that fixes
all these cases.
Referenced Bugs:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103524
[Bug 103524] [meta-bug] modules issue
