[llvm-bugs] [Bug 49576] New: UNREACHABLE executed at LoopFuse.cpp:416!

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=49576

            Bug ID: 49576
           Summary: UNREACHABLE executed at LoopFuse.cpp:416!
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Scalar Optimizations
          Assignee: unassignedbugs at nondot.org
          Reporter: cszide at 163.com
                CC: llvm-bugs at lists.llvm.org

Created attachment 24641
  --> https://bugs.llvm.org/attachment.cgi?id=24641&action=edit
small.bc

$clang -v
clang version 13.0.0 (https://github.com/llvm/llvm-project.git
77394c12a48822bb7a9183408f922d90c1d563cd)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /home/jack-zhou/Documents/llvm/llvm_truck/llvm-project/build/bin
Found candidate GCC installation: /usr/lib/gcc/i686-linux-gnu/8
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/10
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.8
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.8.5
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/5
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/5.5.0
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/6
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/6.5.0
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/7
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/7.5.0
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/8
Selected GCC installation: /usr/lib/gcc/x86_64-linux-gnu/10
Candidate multilib: .;@m64
Selected multilib: .;@m64

$clang -O3 -c -emit-llvm -femit-all-decls -mllvm -disable-llvm-optzns small.c
-o small.bc

$opt -sroa -loop-unswitch  -loop-rotate -early-cse -loop-fusion small.bc -o
small-opt.bc
No dominance relationship between these fusion candidates!
UNREACHABLE executed at
/home/jack-zhou/Documents/llvm/llvm_truck/llvm-project/llvm/lib/Transforms/Scalar/LoopFuse.cpp:416!
PLEASE submit a bug report to https://bugs.llvm.org/ and include the crash
backtrace.
Stack dump:
0.      Program arguments:
/home/jack-zhou/Documents/llvm/llvm_truck/llvm-project/build/bin/opt -sroa
-loop-unswitch -loop-rotate -early-cse -loop-fusion small.bc -o small-opt.bc
1.      Running pass 'Function Pass Manager' on module 'small.bc'.
2.      Running pass 'Loop Fusion' on function '@main'
 #0 0x0000562b92ed05ec llvm::sys::PrintStackTrace(llvm::raw_ostream&, int)
(/home/jack-zhou/Documents/llvm/llvm_truck/llvm-project/build/bin/opt+0x2e865ec)
 #1 0x0000562b92ece2b4 llvm::sys::RunSignalHandlers()
(/home/jack-zhou/Documents/llvm/llvm_truck/llvm-project/build/bin/opt+0x2e842b4)
 #2 0x0000562b92ece423 SignalHandler(int) Signals.cpp:0:0
 #3 0x00007f66754688a0 __restore_rt
(/lib/x86_64-linux-gnu/libpthread.so.0+0x128a0)
 #4 0x00007f66740cff47 raise
/build/glibc-2ORdQG/glibc-2.27/signal/../sysdeps/unix/sysv/linux/raise.c:51:0
 #5 0x00007f66740d18b1 abort /build/glibc-2ORdQG/glibc-2.27/stdlib/abort.c:81:0
 #6 0x0000562b92e2faca
(/home/jack-zhou/Documents/llvm/llvm_truck/llvm-project/build/bin/opt+0x2de5aca)
 #7 0x0000562b92dbf8ba (anonymous
namespace)::FusionCandidateCompare::operator()((anonymous
namespace)::FusionCandidate const&, (anonymous namespace)::FusionCandidate
const&) const (.isra.76) LoopFuse.cpp:0:0
 #8 0x0000562b92dc222b std::pair<std::_Rb_tree_iterator<(anonymous
namespace)::FusionCandidate>, bool> std::_Rb_tree<(anonymous
namespace)::FusionCandidate, (anonymous namespace)::FusionCandidate,
std::_Identity<(anonymous namespace)::FusionCandidate>, (anonymous
namespace)::FusionCandidateCompare, std::allocator<(anonymous
namespace)::FusionCandidate> >::_M_insert_unique<(anonymous
namespace)::FusionCandidate const&>((anonymous namespace)::FusionCandidate
const&) LoopFuse.cpp:0:0
 #9 0x0000562b92dc287a (anonymous
namespace)::LoopFuser::collectFusionCandidates(llvm::SmallVector<llvm::Loop*,
4u> const&) LoopFuse.cpp:0:0
#10 0x0000562b92dcaaeb (anonymous
namespace)::LoopFuser::fuseLoops(llvm::Function&) LoopFuse.cpp:0:0
#11 0x0000562b92dcca63 (anonymous
namespace)::LoopFuseLegacy::runOnFunction(llvm::Function&) LoopFuse.cpp:0:0
#12 0x0000562b9267f918 llvm::FPPassManager::runOnFunction(llvm::Function&)
(/home/jack-zhou/Documents/llvm/llvm_truck/llvm-project/build/bin/opt+0x2635918)
#13 0x0000562b92680449 llvm::FPPassManager::runOnModule(llvm::Module&)
(/home/jack-zhou/Documents/llvm/llvm_truck/llvm-project/build/bin/opt+0x2636449)
#14 0x0000562b9267f196 llvm::legacy::PassManagerImpl::run(llvm::Module&)
(/home/jack-zhou/Documents/llvm/llvm_truck/llvm-project/build/bin/opt+0x2635196)
#15 0x0000562b909c0c0d main
(/home/jack-zhou/Documents/llvm/llvm_truck/llvm-project/build/bin/opt+0x976c0d)
#16 0x00007f66740b2b97 __libc_start_main
/build/glibc-2ORdQG/glibc-2.27/csu/../csu/libc-start.c:344:0
#17 0x0000562b90a89eaa _start
(/home/jack-zhou/Documents/llvm/llvm_truck/llvm-project/build/bin/opt+0xa3feaa)
Aborted (core dumped)

The source code of small.c is as follows.
--------------------------------------------------------
void main() {
  int a, b, c = a = b = 0;
  for (; b < 9; b++)
    if (c)
      ;
  for (; a < 3; a++)
    if (c)
      ;
}

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