[Bug c++/112302] New: The Os optimisation level removes variable value being set in a particular instance

[Bug c++/112302] New: The Os optimisation level removes variable value being set in a particular instance

[barryns86 at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112302

            Bug ID: 112302
           Summary: The Os optimisation level removes variable value being
                    set in a particular instance
           Product: gcc
           Version: 12.3.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: barryns86 at gmail dot com
  Target Milestone: ---

Created attachment 56478
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=56478&action=edit
intermediate build output

When I compile with optimization Os I am getting an over optimization that
breaks my cpp code (variable value is not being set correctly), and I don't see
the issue with O1, O2, or O3. Also Os does not produce the issue on 10.3 (my
current compiler), or earlier versions. but does in all versions of 11 and 12
(that I have tried up to 12.3), and I am trying to update the compiler for a
separate reason. 

I even tried doing O2 but setting the fno version of the flags that Os says it
does not include. That still worked.

In the code, The second parameter (v2) to sub_func2 (within function 1) should
be 25348, not 24580. The thing that is not happening is that variable b4 should
be set to 6, but its not. Its set to zero, no matter what value of "mode" is
passed to function1. I tried to simplify this example down as much as I can. If
you need me to try something else, or need any more info, please ask.


Here is my compile line for the test version of my issue. 
g++ -v -save-temps -Os test.cc -o test

Attached in the ii file produced with 11.4.1 and the issue is present.

And here is the output from the build:
Target: x86_64-redhat-linux

Configured with: ../configure --enable-bootstrap --enable-host-pie
--enable-host-bind-now --enable-languages=c,c++,fortran,lto --prefix=/usr
--mandir=/usr/share/man --infodir=/usr/share/info
--with-bugurl=http://bugzilla.redhat.com/bugzilla --enable-shared
--enable-threads=posix --enable-checking=release --with-system-zlib
--enable-__cxa_atexit --disable-libunwind-exceptions --enable-gnu-unique-object
--enable-linker-build-id --with-gcc-major-version-only --enable-plugin
--enable-initfini-array --without-isl --enable-multilib
--with-linker-hash-style=gnu --enable-offload-targets=nvptx-none
--without-cuda-driver --enable-gnu-indirect-function --enable-cet
--with-tune=generic --with-arch_64=x86-64-v2 --with-arch_32=x86-64
--build=x86_64-redhat-linux --with-build-config=bootstrap-lto
--enable-link-serialization=1

Thread model: posix

Supported LTO compression algorithms: zlib zstd

gcc version 11.4.1 20230605 (Red Hat 11.4.1-2) (GCC) 

COLLECT_GCC_OPTIONS='-v' '-save-temps' '-Os' '-o' 'test' '-shared-libgcc'
'-mtune=generic' '-march=x86-64-v2'

 /usr/libexec/gcc/x86_64-redhat-linux/11/cc1plus -E -quiet -v -D_GNU_SOURCE
test.cc -mtune=generic -march=x86-64-v2 -Os -fpch-preprocess -o test.ii

[Bug middle-end/112302] The Os optimisation level removes variable value being set in a particular instance

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112302

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
This might be undefined code dealing with unions and accesing the fields but
via a pointer outside a function ...

[Bug middle-end/112302] The Os optimisation level removes variable value being set in a particular instance

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112302

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |DUPLICATE
             Status|UNCONFIRMED                 |RESOLVED

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Dup of bug 106389.

*** This bug has been marked as a duplicate of bug 106389 ***

[Bug middle-end/112302] The Os optimisation level removes variable value being set in a particular instance

[barryns86 at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112302

--- Comment #3 from Barry Solomon <barryns86 at gmail dot com> ---
(In reply to Andrew Pinski from comment #2)
> Dup of bug 106389.
> 
> *** This bug has been marked as a duplicate of bug 106389 ***

Thank you very much. I did try looking around, and did not see this other bug.