[llvm-bugs] [Bug 48022] New: Regression: Assertion failure at kmp_dispatch

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=48022

            Bug ID: 48022
           Summary: Regression: Assertion failure at kmp_dispatch
           Product: OpenMP
           Version: unspecified
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: Runtime Library
          Assignee: unassignedbugs at nondot.org
          Reporter: jan-grimo.sobez at phys.chem.ethz.ch
                CC: llvm-bugs at lists.llvm.org

The following code non-deterministically trips a runtime assert on ubuntu 20.04
with the official llvm-apt clang 11 package:

int main() {
#pragma omp parallel for schedule(dynamic)
    for (int c = 0; c < 15; ++c)
#pragma omp parallel
      ;
}

The runtime assert is:
Assertion failure at kmp_dispatch.cpp(1332): victim.
OMP: Error #13: Assertion failure at kmp_dispatch.cpp(1332).
OMP: Hint Please submit a bug [...]

Relevant flags used for building (from CMake-generated Makefile) were:
CXX_FLAGS = -O3 -DNDEBUG   -march=native -fopenmp=libomp

Link command:
/usr/bin/clang++-11  -O3 -DNDEBUG   CMakeFiles/crash.dir/main.cpp.o  -o crash 
/usr/lib/llvm-11/lib/libomp.so /usr/lib/x86_64-linux-gnu/libpthread.so

Execution: no omp env variables set

The code is the result of several iterations of test case minimization and
by-hand refactoring. The interestingness script for the test case minimization
allows up to 100 executions of the program for tripping the assert, so you may
need to repeat execution rapidly for this to trip.

Minimum number of threads I was able to reproduce this with is four. I was
unable to reproduce this with clang 10.

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