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

[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]

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) 
============================================

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

[redi at gcc dot gnu.org]

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

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|                            |2024-05-21
           Keywords|                            |diagnostic,
                   |                            |ice-on-invalid-code,
                   |                            |memory-hog
             Status|UNCONFIRMED                 |NEW
     Ever confirmed|0                           |1

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
I'm marking this as ice-on-invalid-code, even though it gets killed rather than
ICE-ing. But it is invalid.

The summary seems misleading, there are no nested initializer lists here. It's
just syntactically ill-formed code with mismatched braces and parentheses.

And most of the functions are irrelevant to the exponential code.

Reduced:

#include <initializer_list>

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

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(>)
{ } };
}


This seems like auto-generated garbage, not something anybody would ever write
by accident, so should be very low priority.

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

[redi at gcc dot gnu.org]

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

--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Further reduced:

struct string { string(int) { } };

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(>)
{ } };


Still garbage though.