[Bug web/107494] New: -ffinite-loops is not enable by default

[Bug web/107494] New: -ffinite-loops is not enable by default

[570070308 at qq dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107494

            Bug ID: 107494
           Summary: -ffinite-loops is not enable by default
           Product: gcc
           Version: 12.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: web
          Assignee: unassigned at gcc dot gnu.org
          Reporter: 570070308 at qq dot com
  Target Milestone: ---

According to https://gcc.gnu.org/onlinedocs/gcc/Optimize-Options.html

```
-ffinite-loops
Assume that a loop with an exit will eventually take the exit and not loop
indefinitely. This allows the compiler to remove loops that otherwise have no
side-effects, not considering eventual endless looping as such.

This option is enabled by default at -O2 for C++ with -std=c++11 or higher.
```


How ever, it was not enable by default at -O2 for C++ with -std=c++11 or
higher:

```
ig@ig-virtual-machine:~/igc$ /usr/lib/gcc/x86_64-linux-gnu/12/cc1plus
-std=c++11 -O2 --help | grep finite-loops
  -ffinite-loops                        [disabled]
ig@ig-virtual-machine:~/igc$ /usr/lib/gcc/x86_64-linux-gnu/12/cc1plus
-std=gnu++23 -Ofast --help | grep finite-loops
  -ffinite-loops                        [disabled]
```

gcc version:
```
ig@ig-virtual-machine:~/igc$ gcc -v
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/12/lto-wrapper
OFFLOAD_TARGET_NAMES=nvptx-none:amdgcn-amdhsa
OFFLOAD_TARGET_DEFAULT=1
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu 12.2.0-3ubuntu1'
--with-bugurl=file:///usr/share/doc/gcc-12/README.Bugs
--enable-languages=c,ada,c++,go,d,fortran,objc,obj-c++,m2 --prefix=/usr
--with-gcc-major-version-only --program-suffix=-12
--program-prefix=x86_64-linux-gnu- --enable-shared --enable-linker-build-id
--libexecdir=/usr/lib --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-offload-targets=nvptx-none=/build/gcc-12-U8K4Qv/gcc-12-12.2.0/debian/tmp-nvptx/usr,amdgcn-amdhsa=/build/gcc-12-U8K4Qv/gcc-12-12.2.0/debian/tmp-gcn/usr
--enable-offload-defaulted --without-cuda-driver --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 12.2.0 (Ubuntu 12.2.0-3ubuntu1) 
ig@ig-virtual-machine:~/igc$
```

[Bug middle-end/107494] -ffinite-loops is not enable by default

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107494

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |diagnostic
          Component|web                         |middle-end

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
It definitely it is enabled:

  /* C++11 guarantees forward progress.  */
  SET_OPTION_IF_UNSET (&global_options, &global_options_set, flag_finite_loops,
                       optimize >= 2 && cxx_dialect >= cxx11);


option processing and showing --help sometimes does nto always agree.

[Bug middle-end/107494] -ffinite-loops does not show it is enabled with --help by default for C++11+

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107494

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
     Ever confirmed|0                           |1
            Summary|-ffinite-loops is not       |-ffinite-loops does not
                   |enable by default           |show it is enabled with
                   |                            |--help by default for
                   |                            |C++11+
   Last reconfirmed|                            |2022-11-28
             Status|UNCONFIRMED                 |NEW

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Confirmed.

  /* Exit early if we can (e.g. -help).  */
  if (!exit_after_options)
    {
      /* Just in case lang_hooks.post_options ends up calling a debug_hook.
         This can happen with incorrect pre-processed input. */
      debug_hooks = &do_nothing_debug_hooks;
      /* Allow the front end to perform consistency checks and do further
         initialization based on the command line options.  This hook also
         sets the original filename if appropriate (e.g. foo.i -> foo.c)
         so we can correctly initialize debug output.  */
      bool no_backend = lang_hooks.post_options (&main_input_filename);


So the language hook that does the SET_OPTION_IF_UNSET is not called at all.