[Bug c++/106863] New: internal compiler error: in write_template_arg_literal, at cp/mangle.cc:3678

[Bug c++/106863] New: internal compiler error: in write_template_arg_literal, at cp/mangle.cc:3678

[jehova at existiert dot net]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106863

            Bug ID: 106863
           Summary: internal compiler error: in
                    write_template_arg_literal, at cp/mangle.cc:3678
           Product: gcc
           Version: 12.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: jehova at existiert dot net
  Target Milestone: ---

$ g++ --version
g++ (GCC) 12.2.0
Copyright (C) 2022 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.


$ g++ -c bug.cxx -freport-bug
bug.cxx: In instantiation of ‘decltype ((g(t), (void)0)) f(T) [with T = int]’:
bug.cxx:4:6: internal compiler error: in write_template_arg_literal, at
cp/mangle.cc:3678
    4 | auto f(T t) -> decltype(g(t), void{})
      |      ^
0x19eab38 internal_error(char const*, ...)
        ???:0
0x6546f4 fancy_abort(char const*, int, char const*)
        ???:0
0x728a60 mangle_decl(tree_node*)
        ???:0
0x984016 symbol_table::finalize_compilation_unit()
        ???:0
Please submit a full bug report, with preprocessed source.
Please include the complete backtrace with any bug report.
See <https://bugs.archlinux.org/> for instructions.
Preprocessed source stored into /tmp/ccL1sCjr.out file, please attach this to
your bugreport.


$ cat bug.cxx 
void g(int);

template <typename T>
auto f(T t) -> decltype(g(t), void{})
{
   return g(t);
}

int main()
{
   f(0);
}


$ cat ccL1sCjr.out 
// Target: x86_64-pc-linux-gnu
// Configured with: /build/gcc/src/gcc/configure
--enable-languages=c,c++,ada,fortran,go,lto,objc,obj-c++,d --enable-bootstrap
--prefix=/usr --libdir=/usr/lib --libexecdir=/usr/lib --mandir=/usr/share/man
--infodir=/usr/share/info --with-bugurl=https://bugs.archlinux.org/
--with-build-config=bootstrap-lto --with-linker-hash-style=gnu
--with-system-zlib --enable-__cxa_atexit --enable-cet=auto
--enable-checking=release --enable-clocale=gnu --enable-default-pie
--enable-default-ssp --enable-gnu-indirect-function --enable-gnu-unique-object
--enable-libstdcxx-backtrace --enable-link-serialization=1
--enable-linker-build-id --enable-lto --enable-multilib --enable-plugin
--enable-shared --enable-threads=posix --disable-libssp --disable-libstdcxx-pch
--disable-werror
// Thread model: posix
// Supported LTO compression algorithms: zlib zstd
// gcc version 12.2.0 (GCC) 
// 
// bug.cxx: In instantiation of ‘decltype ((g(t), (void)0)) f(T) [with T =
int]’:
// bug.cxx:4:6: internal compiler error: in write_template_arg_literal, at
cp/mangle.cc:3678
//     4 | auto f(T t) -> decltype(g(t), void{})
//       |      ^
// 0x19eab38 internal_error(char const*, ...)
//      ???:0
// 0x6546f4 fancy_abort(char const*, int, char const*)
//      ???:0
// 0x728a60 mangle_decl(tree_node*)
//      ???:0
// 0x984016 symbol_table::finalize_compilation_unit()
//      ???:0
// Please submit a full bug report, with preprocessed source.
// Please include the complete backtrace with any bug report.
// See <https://bugs.archlinux.org/> for instructions.

// /usr/lib/gcc/x86_64-pc-linux-gnu/12.2.0/cc1plus -quiet -D_GNU_SOURCE bug.cxx
-quiet -dumpbase bug.cxx -dumpbase-ext .cxx -mtune=generic -march=x86-64
-freport-bug -o - -frandom-seed=0 -fdump-noaddr

# 0 "bug.cxx"
# 0 "<built-in>"
# 0 "<command-line>"
# 1 "/usr/include/stdc-predef.h" 1 3 4
# 0 "<command-line>" 2
# 1 "bug.cxx"
void g(int);

template <typename T>
auto f(T t) -> decltype(g(t), void{})
{
   return g(t);
}

int main()
{
   f(0);
}

[Bug c++/106863] ICE in write_template_arg_literal, at cp/mangle.cc:3678 since r12-4782-geca767aa51d1f696

[marxin at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106863

Martin Liška <marxin at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
     Ever confirmed|0                           |1
            Summary|internal compiler error: in |ICE in
                   |write_template_arg_literal, |write_template_arg_literal,
                   |at cp/mangle.cc:3678        |at cp/mangle.cc:3678 since
                   |                            |r12-4782-geca767aa51d1f696
   Last reconfirmed|                            |2022-09-07
                 CC|                            |jakub at gcc dot gnu.org,
                   |                            |marxin at gcc dot gnu.org

--- Comment #1 from Martin Liška <marxin at gcc dot gnu.org> ---
Started with r12-4782-geca767aa51d1f696, rejected before.

[Bug c++/106863] ICE in write_template_arg_literal, at cp/mangle.cc:3678 since r12-4782-geca767aa51d1f696

[jehova at existiert dot net]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106863

--- Comment #2 from jehova at existiert dot net ---
I'm not sure if 'ice-on-valid-code' is appropriate here, since the example code
is *not* valid.
It is if 'void{}' is replaced by 'void()' (which is perfectly accepted by GCC).

[Bug c++/106863] ICE in write_template_arg_literal, at cp/mangle.cc:3678 since r12-4782-geca767aa51d1f696

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106863

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED
           Assignee|unassigned at gcc dot gnu.org      |jakub at gcc dot gnu.org

--- Comment #3 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Created attachment 53722
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=53722&action=edit
gcc13-pr106863.patch

If we can mangle void{} the same as void(), then this patch achieves that
(or we could call build_functional_cast always, but for
!processing_template_decl it will in the end just return void_node).
Otherwise, we'd need to mangle void_node somehow (how?), but void_node doesn't
always imply void{}, it is created for many other cases.

[Bug c++/106863] ICE in write_template_arg_literal, at cp/mangle.cc:3678 since r12-4782-geca767aa51d1f696

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106863

--- Comment #4 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
And it is valid,
https://www.open-std.org/jtc1/sc22/wg21/docs/cwg_defects.html#2351
was applied as a DR to C++11 and later.

[Bug c++/106863] ICE in write_template_arg_literal, at cp/mangle.cc:3678 since r12-4782-geca767aa51d1f696

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106863

--- Comment #5 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Jakub Jelinek <jakub@gcc.gnu.org>:

https://gcc.gnu.org/g:5f9fac6ca86458ef21ab91ca471429d63f954003

commit r13-3429-g5f9fac6ca86458ef21ab91ca471429d63f954003
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Fri Oct 21 09:00:41 2022 +0200

    c++: Fix up mangling ICE with void{} [PR106863]

    We ICE on the following testcase during mangling, finish_compound_literal
    returns for void{} void_node and the mangler doesn't handle it.
    Handling void_node in the mangler seems problematic to me, because
    we don't know for which case it has been created.
    The following patch arranges to mangle it as other compound literals
    with no operands, so it demangles as void{}, by returning a void type
    COMPOUND_LITERAL_P with no elements if processing_template_decl.
    Otherwise it keeps returning void_node.

    2022-10-21  Jakub Jelinek  <jakub@redhat.com>

            PR c++/106863
            * semantics.cc (finish_compound_literal): For void{}, if
            processing_template_decl return a COMPOUND_LITERAL_P
            CONSTRUCTOR rather than void_node.

            * g++.dg/cpp0x/dr2351-2.C: New test.