[flang][openmp] initialize allocatable components of firstprivate copies (#121808)

Descriptors of allocatable components of firstprivate derived type
copies need to be set-up. Otherwise the program later die when
manipulating them inside OpenMP region.

Author: jeanPerier

flang/lib/Lower/Bridge.cpp

@@ -833,7 +833,11 @@ class FirConverter : public Fortran::lower::AbstractConverter {
           if_builder.end();
         },
         [&](const auto &) -> void {
-          if (skipDefaultInit)
+          // Always initialize allocatable component descriptor, even when the
+          // value is later copied from the host (e.g. firstprivate) because the
+          // assignment from the host to the copy will fail if the component
+          // descriptors are not initialized.
+          if (skipDefaultInit && !hlfir::mayHaveAllocatableComponent(hSymType))
             return;
           // Initialize local/private derived types with default
           // initialization (Fortran 2023 section 11.1.7.5 and OpenMP 5.2

flang/test/Lower/OpenMP/firstprivate-alloc-comp.f90

@@ -0,0 +1,19 @@
+! Test delayed privatization for derived types with allocatable components.
+! RUN: %flang_fc1 -emit-hlfir -fopenmp -o - %s | FileCheck %s
+
+subroutine firstprivate_alloc_comp
+  type t1
+    integer, allocatable :: c(:)
+  end type
+  type(t1) :: x
+  !$omp parallel firstprivate(x)
+    print *, allocated(x%c)
+  !$omp end parallel
+end
+
+  call firstprivate_alloc_comp()
+end
+! CHECK-LABEL:   omp.private {type = firstprivate} @_QFfirstprivate_alloc_compEx_firstprivate_ref_rec__QFfirstprivate_alloc_compTt1 : !fir.ref<!fir.type<_QFfirstprivate_alloc_compTt1{c:!fir.box<!fir.heap<!fir.array<?xi32>>>}>> alloc {
+! CHECK:     fir.call @_FortranAInitialize(
+! CHECK:   } copy {
+! ...