[Bug c++/124084] New: Gem5 miscomputes with gcc 16

[kugan at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=124084

            Bug ID: 124084
           Summary: Gem5 miscomputes with gcc 16
           Product: gcc
           Version: 16.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: kugan at gcc dot gnu.org
  Target Milestone: ---

Created attachment 63657
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=63657&action=edit
testcase

GGC 16 regresses for the attached test case (reduced from gem5). Bisect points
to bc42128330c0ea70a015b74b655cb8c48b6a8c06 but AFIK it just exposes it.

gcc -v
Using built-in specs.
COLLECT_GCC=../install/bin/gcc
COLLECT_LTO_WRAPPER=/mnt/scratch.grco_devs3/kvivekananda/hierarchical/install/libexec/gcc/aarch64-unknown-linux-gnu/16.0.1/lto-wrapper
Target: aarch64-unknown-linux-gnu
Configured with:
/mnt/scratch.grco_devs3/kvivekananda/hierarchical/gcc/configure
--prefix=/mnt/scratch.grco_devs3/kvivekananda/hierarchical/install
--disable-bootstrap --enable-languages=c,c++,fortran,lto
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 16.0.1 20260121 (experimental) (GCC)