https://gcc.gnu.org/bugzilla/show_bug.cgi?id=125677
Bug ID: 125677
Summary: The C++ frontend fails to reject an invalid un-deduced
auto in a trailing return type when forming a function
reference type for a variable template instantiation.
This invalid AST is then passed to the backend,
causing a Segmentation fault (ICE) during t
Product: gcc
Version: 13.4.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: 1794833681 at qq dot com
Target Milestone: ---
Description:
The C++ frontend fails to reject an invalid un-deduced auto in a trailing
return type when forming a function reference type for a variable template
instantiation. This invalid AST is then passed to the backend, causing a
Segmentation fault (ICE) during the RTL expansion phase.
Minimal Reproducible Example:
C++
template <typename a>
inline constexpr bool t = false;
int main()
{
return t<auto(&)(const int*) -> auto&>;
}
Command Line Arguments:
Bash
g++ -std=c++23 source.cpp
Tested Versions:
Reproduced on: x86-64 gcc 11.3 up to x86-64 gcc 13.4 (including builds with
assertions enabled).
Compiler Output / Backtrace:
Plaintext
<source>: In function 'int main()':
<source>:6:12: internal compiler error: Segmentation fault
6 | return t<auto(&)(const int*) -> auto&>;
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
0x1bb069e internal_error(char const*, ...)
???:0
0x10eb0c3 make_decl_rtl(tree_node*)
???:0
0xaa8bc3 expand_expr_real_1(tree_node*, rtx_def*, machine_mode,
expand_modifier, rtx_def**, bool)
???:0
0xab4219 store_expr(tree_node*, rtx_def*, int, bool, bool)
???:0
Please submit a full bug report, with preprocessed source (by using
-freport-bug).
Expected Behavior:
The compiler should gracefully reject the code and emit a syntax or type error
regarding the invalid use of auto in the function prototype without a valid
deduction context, rather than crashing in the backend.
