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From: "slyfox at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug middle-end/110515] New: [14 Regression] llvm-15.0.7 possibly
 invalid code on -O3
Date: Sat, 01 Jul 2023 21:52:54 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D110515

            Bug ID: 110515
           Summary: [14 Regression] llvm-15.0.7 possibly invalid code on
                    -O3
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
          Assignee: unassigned at gcc dot gnu.org
          Reporter: slyfox at gcc dot gnu.org
  Target Milestone: ---

Created attachment 55447
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=3D55447&action=3Dedit
DwarfCompileUnit.cpp

Initially the failure is observed on r14-2233-gfca6d9c12f5bf0 where llvm-15=
.0.7
test suite fails a single test:

  Failed Tests (1):
    LLVM :: DebugInfo/X86/vla-multi.ll

I think I shrunk it down to DwarfCompileUnit.cpp:

$ g++ -std=3Dc++14 DwarfCompileUnit.cpp -O2 $cxxflags -o bug-O2 && ./bug-O2
Illegal instruction (core dumped)
$ g++ -std=3Dc++14 DwarfCompileUnit.cpp -O1 $cxxflags -o bug-O1 && ./bug-O1
<ok>

It's a very fragile test:
- any inlines I try seem to repair the test
- -fno-strict-aliasing unbreaks it (I believe the code is strict-aliasing
clean)
- optimization option changes repair the test

$ g++ -v
Using built-in specs.
COLLECT_GCC=3D/<<NIX>>/gcc-14.0.0/bin/g++
COLLECT_LTO_WRAPPER=3D/<<NIX>>/gcc-14.0.0/libexec/gcc/x86_64-unknown-linux-=
gnu/14.0.0/lto-wrapper
Target: x86_64-unknown-linux-gnu
Configured with:
Thread model: posix
Supported LTO compression algorithms: zlib
gcc version 14.0.0 99999999 (experimental) (GCC)=