[Bug c++/115173] New: GCC hang and memory exhaustion issue with complex nested initializer lists in C++ std::string construction

["iamanonymous.cs at gmail dot com" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115173

            Bug ID: 115173
           Summary: GCC hang and memory exhaustion issue with complex
                    nested initializer lists in C++ std::string
                    construction
           Product: gcc
           Version: 13.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: iamanonymous.cs at gmail dot com
  Target Milestone: ---

The following code snippet triggers a hang issue:
============================================
$ cat bug.cpp

#include <initializer_list>

struct string { string(std::initializer_list<char>) { } };

void f() {
  string({});
}
void g() {
  string(string({}); 
}
void h() {
  string(string({}));
}
void i() {
  string(string(string({}));
}
void j() {
 
string(string(string(string(string(string(string(string(string(string(string(string(string(string(string(string(string(string(string(string(string(string(string(string(string(string(string(string(string(string(string(string(string(string(string(string(string(string(string(string(string(string(string(string(string(string(string(string(string(string(string(>)
{ } };

void f() {
  auto y =
  {
    string(Equation()) 
  }; 
}
============================================
I observed that when attempting to compile this code using GCC, the compilation
process hangs indefinitely. Additionally, the RAM usage continuously increases,
leading to excessive consumption of system resources.

However, it is worth noting that when using LLVM as the compiler, the code
compiles quickly and produces the expected compilation output.

We have found that this issue still persists in the latest version of GCC(see
https://godbolt.org/z/oKKe5WK9v)

The command we used is(no error output):
============================================
g++ bug.cpp
============================================


The GCC version:
============================================
$ gcc -v
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/libexec/gcc/x86_64-linux-gnu/13/lto-wrapper
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu
13.1.0-8ubuntu1~20.04.2' --with-bugurl=file:///usr/share/doc/gcc-13/README.Bugs
--enable-languages=c,ada,c++,go,d,fortran,objc,obj-c++,m2,rust --prefix=/usr
--with-gcc-major-version-only --program-suffix=-13
--program-prefix=x86_64-linux-gnu- --enable-shared --enable-linker-build-id
--libexecdir=/usr/libexec --without-included-gettext --enable-threads=posix
--libdir=/usr/lib --enable-nls --enable-clocale=gnu --enable-libstdcxx-debug
--enable-libstdcxx-time=yes --with-default-libstdcxx-abi=new
--enable-gnu-unique-object --disable-vtable-verify --enable-plugin
--enable-default-pie --with-system-zlib --enable-libphobos-checking=release
--with-target-system-zlib=auto --enable-objc-gc=auto --enable-multiarch
--disable-werror --enable-cet --with-arch-32=i686 --with-abi=m64
--with-multilib-list=m32,m64,mx32 --enable-multilib --with-tune=generic
--enable-checking=release --build=x86_64-linux-gnu --host=x86_64-linux-gnu
--target=x86_64-linux-gnu
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 13.1.0 (Ubuntu 13.1.0-8ubuntu1~20.04.2) 
============================================