[Flang][OpenMP] Assertion `success && "Privatization failed due to existing binding"' failed. (parallel sections directive)

[k-arrows]

Reproducer:

!$omp parallel sections
!$omp section
    do i = 1, 2
    end do
!$omp section
    do i = 1, 2
    end do
!$omp end parallel sections
end

With assertion-disabled flang, the following output is obtained:
https://godbolt.org/z/GbfW7vYKj

flang-21: warning: OpenMP support in flang is still experimental [-Wexperimental-option]
error: loc("/app/example.f90":6:5): operand #1 does not dominate this use
error: verification of lowering to FIR failed
Compiler returned: 1

With assertion-enabled flang, the reproducer hits the following assertion:

flang: /path_to_project/llvm-project/flang/lib/Lower/OpenMP/DataSharingProcessor.cpp:152: void Fortran::lower::omp::DataSharingProcessor::cloneSymbol(const semantics::Symbol *): Assertion `success && "Privatization failed due to existing binding"' failed.

[k-arrows]

The fact that the same loop variable is used in both the first and second loop in the reproducer may be essential. In fact, the following program compiles without any problems.

!$omp parallel sections
!$omp section
    do i = 1, 2
    end do
!$omp section
    do j = 1, 2
    end do
!$omp end parallel sections
end

[llvmbot]

@llvm/issue-subscribers-flang-ir

Author: None (k-arrows)

Reproducer: ```f90 !$omp parallel sections !$omp section do i = 1, 2 end do !$omp section do i = 1, 2 end do !$omp end parallel sections end ```

With assertion-disabled flang, the following output is obtained:
https://godbolt.org/z/GbfW7vYKj

flang-21: warning: OpenMP support in flang is still experimental [-Wexperimental-option]
error: loc("/app/example.f90":6:5): operand #<!-- -->1 does not dominate this use
error: verification of lowering to FIR failed
Compiler returned: 1

With assertion-enabled flang, the reproducer hits the following assertion:

flang: /path_to_project/llvm-project/flang/lib/Lower/OpenMP/DataSharingProcessor.cpp:152: void Fortran::lower::omp::DataSharingProcessor::cloneSymbol(const semantics::Symbol *): Assertion `success && "Privatization failed due to existing binding"' failed.