[llvm] [mlir] [mlir][OpenMP] - Implement lowering from MLIR to LLVMIR for `private` clause on `target` constructs (PR #105471)

[Christian Ulmann via llvm-commits]

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+! Test target private
+! REQUIRES: flang, amdgcn-amd-amdhsa
+! UNSUPPORTED: nvptx64-nvidia-cuda
+! UNSUPPORTED: nvptx64-nvidia-cuda-LTO
+! UNSUPPORTED: aarch64-unknown-linux-gnu
+! UNSUPPORTED: aarch64-unknown-linux-gnu-LTO
+! UNSUPPORTED: x86_64-pc-linux-gnu
+! UNSUPPORTED: x86_64-pc-linux-gnu-LTO
+
+! RUN: %libomptarget-compile-fortran-run-and-check-generic
+program main
+  integer :: a = 0
+  call target_private(a)
+  print*, "======= FORTRAN Test passed! ======="
+  print*, "foo(a) should not return 20, got " , a
+  if (a /= 20) then
+     stop 0
+  else
+     stop 1
+  end if
+  
+  !       stop 0
+end program main
+subroutine target_private(r)
+  implicit none
+  integer, dimension(2) :: simple_vars
+  integer :: a, r
+  ! set a to 10
+  a = 5
+  simple_vars(1) = a
+  simple_vars(2) = a
+  !$omp target map(tofrom: simple_vars) private(a)
+  ! Without private(a), a would be firstprivate, meaning it's value would be 5
+  ! with private(a), it's value would be uninitialized, which means it'd have
+  ! a very small chance of being 5.
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Dinistro wrote:

Ultra nit: This case is UB, so anything can happen. Not sure if there would be another case that would not invoke UB in case of missing `private` support?

https://github.com/llvm/llvm-project/pull/105471