[Flang][OpenMP] Assertion `(&MBB != &MBB.getParent()->front() || IgnoreMissingDefs) && "no reload in start block. Missing vreg def?"' failed.

[k-arrows]

Reproducer:

integer :: x
!$omp parallel private (x)
!$omp task shared (x) depend(out: x)
!$omp end task
!$omp end parallel
end

Assertion failure:

llvm-project/llvm/lib/CodeGen/RegAllocFast.cpp:696: void (anonymous namespace)::RegAllocFastImpl::reloadAtBegin(llvm::MachineBasicBlock &): Assertion `(&MBB != &MBB.getParent()->front() || IgnoreMissingDefs) && "no reload in start block. Missing vreg def?"' failed.

Stack dump:

 #0 0x00007f6a73a167d7 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int)
 #1 0x00007f6a73a1436e llvm::sys::RunSignalHandlers()
 #2 0x00007f6a73a16eaa SignalHandler(int) Signals.cpp:0:0
 #3 0x00007f6a73347520 (/lib/x86_64-linux-gnu/libc.so.6+0x42520)
 #4 0x00007f6a7339b9fc __pthread_kill_implementation ./nptl/pthread_kill.c:44:76
 #5 0x00007f6a7339b9fc __pthread_kill_internal ./nptl/pthread_kill.c:78:10
 #6 0x00007f6a7339b9fc pthread_kill ./nptl/pthread_kill.c:89:10
 #7 0x00007f6a73347476 gsignal ./signal/../sysdeps/posix/raise.c:27:6
 #8 0x00007f6a7332d7f3 abort ./stdlib/abort.c:81:7
 #9 0x00007f6a7332d71b _nl_load_domain ./intl/loadmsgcat.c:1177:9
#10 0x00007f6a7333ee96 (/lib/x86_64-linux-gnu/libc.so.6+0x39e96)
#11 0x00007f6a724b86ac (anonymous namespace)::RegAllocFastImpl::runOnMachineFunction(llvm::MachineFunction&) RegAllocFast.cpp:0:0
#12 0x00007f6a724c4a3a (anonymous namespace)::RegAllocFast::runOnMachineFunction(llvm::MachineFunction&) RegAllocFast.cpp:0:0
#13 0x00007f6a722d40c4 llvm::MachineFunctionPass::runOnFunction(llvm::Function&)
#14 0x00007f6a70c6196b llvm::FPPassManager::runOnFunction(llvm::Function&) 
#15 0x00007f6a70c698a1 llvm::FPPassManager::runOnModule(llvm::Module&) 
#16 0x00007f6a70c6237f llvm::legacy::PassManagerImpl::run(llvm::Module&) 
#17 0x00007f6a747f4b49 Fortran::frontend::CodeGenAction::executeAction() 
#18 0x00007f6a747e91ac Fortran::frontend::FrontendAction::execute() 
#19 0x00007f6a747cf0e2 Fortran::frontend::CompilerInstance::executeAction(Fortran::frontend::FrontendAction&) 
#20 0x00007f6a7496737c Fortran::frontend::executeCompilerInvocation(Fortran::frontend::CompilerInstance*) 
#21 0x0000558a1e9d3433 fc1_main(llvm::ArrayRef<char const*>, char const*) 
#22 0x0000558a1e9d197a main 
#23 0x00007f6a7332ed90 __libc_start_call_main ./csu/../sysdeps/nptl/libc_start_call_main.h:58:16
#24 0x00007f6a7332ee40 call_init ./csu/../csu/libc-start.c:128:20
#25 0x00007f6a7332ee40 __libc_start_main ./csu/../csu/libc-start.c:379:5
#26 0x0000558a1e9d1495 _start 
flang-20: error: unable to execute command: Aborted (core dumped)
flang-20: error: flang frontend command failed due to signal (use -v to see invocation)
flang version 20.0.0git (https://github.com/llvm/llvm-project.git cb1ad985b53c87b53974e37bba60129acb294f0d)
Target: x86_64-unknown-linux-gnu
Thread model: posix

[k-arrows]

Specifying -O1 or higher as the optimization level leads to another assertion failure.

llvm-project/llvm/lib/Transforms/Utils/ValueMapper.cpp:976: void (anonymous namespace)::Mapper::remapInstruction(llvm::Instruction *): Assertion `(Flags & RF_IgnoreMissingLocals) && "Referenced value not in value map!"' failed.

[llvmbot]

@llvm/issue-subscribers-flang-ir

Author: None (k-arrows)

Reproducer: ```f90 integer :: x !$omp parallel private (x) !$omp task shared (x) depend(out: x) !$omp end task !$omp end parallel end ```

Assertion failure:

llvm-project/llvm/lib/CodeGen/RegAllocFast.cpp:696: void (anonymous namespace)::RegAllocFastImpl::reloadAtBegin(llvm::MachineBasicBlock &): Assertion `(&MBB != &MBB.getParent()->front() || IgnoreMissingDefs) && "no reload in start block. Missing vreg def?"' failed.

Stack dump:

 #<!-- -->0 0x00007f6a73a167d7 llvm::sys::PrintStackTrace(llvm::raw_ostream&amp;, int)
 #<!-- -->1 0x00007f6a73a1436e llvm::sys::RunSignalHandlers()
 #<!-- -->2 0x00007f6a73a16eaa SignalHandler(int) Signals.cpp:0:0
 #<!-- -->3 0x00007f6a73347520 (/lib/x86_64-linux-gnu/libc.so.6+0x42520)
 #<!-- -->4 0x00007f6a7339b9fc __pthread_kill_implementation ./nptl/pthread_kill.c:44:76
 #<!-- -->5 0x00007f6a7339b9fc __pthread_kill_internal ./nptl/pthread_kill.c:78:10
 #<!-- -->6 0x00007f6a7339b9fc pthread_kill ./nptl/pthread_kill.c:89:10
 #<!-- -->7 0x00007f6a73347476 gsignal ./signal/../sysdeps/posix/raise.c:27:6
 #<!-- -->8 0x00007f6a7332d7f3 abort ./stdlib/abort.c:81:7
 #<!-- -->9 0x00007f6a7332d71b _nl_load_domain ./intl/loadmsgcat.c:1177:9
#<!-- -->10 0x00007f6a7333ee96 (/lib/x86_64-linux-gnu/libc.so.6+0x39e96)
#<!-- -->11 0x00007f6a724b86ac (anonymous namespace)::RegAllocFastImpl::runOnMachineFunction(llvm::MachineFunction&amp;) RegAllocFast.cpp:0:0
#<!-- -->12 0x00007f6a724c4a3a (anonymous namespace)::RegAllocFast::runOnMachineFunction(llvm::MachineFunction&amp;) RegAllocFast.cpp:0:0
#<!-- -->13 0x00007f6a722d40c4 llvm::MachineFunctionPass::runOnFunction(llvm::Function&amp;)
#<!-- -->14 0x00007f6a70c6196b llvm::FPPassManager::runOnFunction(llvm::Function&amp;) 
#<!-- -->15 0x00007f6a70c698a1 llvm::FPPassManager::runOnModule(llvm::Module&amp;) 
#<!-- -->16 0x00007f6a70c6237f llvm::legacy::PassManagerImpl::run(llvm::Module&amp;) 
#<!-- -->17 0x00007f6a747f4b49 Fortran::frontend::CodeGenAction::executeAction() 
#<!-- -->18 0x00007f6a747e91ac Fortran::frontend::FrontendAction::execute() 
#<!-- -->19 0x00007f6a747cf0e2 Fortran::frontend::CompilerInstance::executeAction(Fortran::frontend::FrontendAction&amp;) 
#<!-- -->20 0x00007f6a7496737c Fortran::frontend::executeCompilerInvocation(Fortran::frontend::CompilerInstance*) 
#<!-- -->21 0x0000558a1e9d3433 fc1_main(llvm::ArrayRef&lt;char const*&gt;, char const*) 
#<!-- -->22 0x0000558a1e9d197a main 
#<!-- -->23 0x00007f6a7332ed90 __libc_start_call_main ./csu/../sysdeps/nptl/libc_start_call_main.h:58:16
#<!-- -->24 0x00007f6a7332ee40 call_init ./csu/../csu/libc-start.c:128:20
#<!-- -->25 0x00007f6a7332ee40 __libc_start_main ./csu/../csu/libc-start.c:379:5
#<!-- -->26 0x0000558a1e9d1495 _start 
flang-20: error: unable to execute command: Aborted (core dumped)
flang-20: error: flang frontend command failed due to signal (use -v to see invocation)
flang version 20.0.0git (https://github.com/llvm/llvm-project.git cb1ad985b53c87b53974e37bba60129acb294f0d)
Target: x86_64-unknown-linux-gnu
Thread model: posix