[Bug c++/114858] New: Compilation Hang and Excessive RAM Consumption in GCC

[Bug c++/114858] New: Compilation Hang and Excessive RAM Consumption in GCC

[iamanonymous.cs at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114858

            Bug ID: 114858
           Summary: Compilation Hang and Excessive RAM Consumption in GCC
           Product: gcc
           Version: 14.0
            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

template <class F> void g(F);
template <class... A>
auto h(A &&... a) -> decltype(g(0,
(g<decltype(g<decltype(g<decltype(g<decltype(g<decltype(g<decltype(g<decltype(g<decltype(g<decltype(g<decltype(g<decltype(g<decltype(g<decltype(g<decltype(g<decltype(g<decltype(g<decltype(g<decltype(g<decltype(g<decltype(g<decltype(g<decltype(g<decltype(g<decltype(g<decltype(g<decltype(g<decltype(g<decltype(g<decltype(g<decltype(g<decltype(g<decltype(g<decltype()>)(a)...))
{
  h([] {});
}

int main() { 
  h(); 
  return 0; 
}
============================================
I observed that when attempting to compile this code using GCC, the compilation
process hangs indefinitely, without providing any output or indicating
successful compilation. 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/P1c7f664f)

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=/home/cTest/gcc/myinstall/libexec/gcc/x86_64-linux-gnu/14.0.1/lto-wrapper
Target: x86_64-linux-gnu
Configured with: ../configure -v --build=x86_64-linux-gnu
--host=x86_64-linux-gnu --target=x86_64-linux-gnu --enable-checking=no
--enable-languages=c,c++ --disable-multilib --prefix=/home/cTest/gcc/myinstall
--disable-bootstrap
Thread model: posix
Supported LTO compression algorithms: zlib
gcc version 14.0.1 20240329 (experimental) (GCC) 
============================================

[Bug c++/114858] [11/12/13/14 regression] Compilation Hang and Excessive RAM Consumption in GCC

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114858

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
      Known to fail|                            |4.8.4, 4.8.5
      Known to work|                            |4.8.2, 4.8.3
   Target Milestone|---                         |11.5
            Summary|Compilation Hang and        |[11/12/13/14 regression]
                   |Excessive RAM Consumption   |Compilation Hang and
                   |in GCC                      |Excessive RAM Consumption
                   |                            |in GCC

[Bug c++/114858] [11/12/13/14 regression] Compilation Hang and Excessive RAM Consumption in GCC with invalid input

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114858

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
     Ever confirmed|0                           |1
            Summary|[11/12/13/14 regression]    |[11/12/13/14 regression]
                   |Compilation Hang and        |Compilation Hang and
                   |Excessive RAM Consumption   |Excessive RAM Consumption
                   |in GCC                      |in GCC with invalid input
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2024-04-26

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Confirmed. Looks like a patch which was backported to the GCC 4.8.4 release is
the cause.

[Bug c++/114858] [11/12/13/14 regression] Compilation Hang and Excessive RAM Consumption in GCC with invalid input since r0-128725

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114858

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|[11/12/13/14 regression]    |[11/12/13/14 regression]
                   |Compilation Hang and        |Compilation Hang and
                   |Excessive RAM Consumption   |Excessive RAM Consumption
                   |in GCC with invalid input   |in GCC with invalid input
                   |                            |since r0-128725
                 CC|                            |jakub at gcc dot gnu.org,
                   |                            |jason at gcc dot gnu.org,
                   |                            |ppalka at gcc dot gnu.org

--- Comment #2 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Seems it started to hang with
r0-128725-g5d264d62dc6d381510bea36469d50175fa6a39c2
Before that commit it has been rejected with many errors.

[Bug c++/114858] [11/12/13/14/15 regression] Compilation Hang and Excessive RAM Consumption in GCC with invalid input since r0-128725

[hp at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114858

--- Comment #3 from Hans-Peter Nilsson <hp at gcc dot gnu.org> ---
Looks like it slowly chews up memory.  I killed an -O2 run when cc1plus had
consumed 110 GiB, x86_64-linux at r14-10114-g09680e3ee7d7.