[13/14] OpenACC: Allow implicit uses of assumed-size arrays in offload regions

diff --git a/gcc/fortran/trans-openmp.cc b/gcc/fortran/trans-openmp.cc
index 819d79cda28..230cebf250b 100644
--- a/gcc/fortran/trans-openmp.cc
+++ b/gcc/fortran/trans-openmp.cc
@@ -1587,6 +1587,7 @@  gfc_omp_finish_clause (tree c, gimple_seq *pre_p, bool openacc)
     return;
 
   tree decl = OMP_CLAUSE_DECL (c);
+  bool assumed_size = false;
 
   /* Assumed-size arrays can't be mapped implicitly, they have to be
      mapped explicitly using array sections.  */
@@ -1597,9 +1598,14 @@  gfc_omp_finish_clause (tree c, gimple_seq *pre_p, bool openacc)
 				GFC_TYPE_ARRAY_RANK (TREE_TYPE (decl)) - 1)
 	 == NULL)
     {
-      error_at (OMP_CLAUSE_LOCATION (c),
-		"implicit mapping of assumed size array %qD", decl);
-      return;
+      if (openacc)
+	assumed_size = true;
+      else
+	{
+	  error_at (OMP_CLAUSE_LOCATION (c),
+		    "implicit mapping of assumed size array %qD", decl);
+	  return;
+	}
     }
 
   if (OMP_CLAUSE_MAP_KIND (c) == GOMP_MAP_FORCE_DEVICEPTR)
@@ -1654,7 +1660,9 @@  gfc_omp_finish_clause (tree c, gimple_seq *pre_p, bool openacc)
       else
 	{
 	  OMP_CLAUSE_DECL (c) = decl;
-	  OMP_CLAUSE_SIZE (c) = NULL_TREE;
+	  OMP_CLAUSE_SIZE (c) = assumed_size ? size_zero_node : NULL_TREE;
+	  if (assumed_size)
+	    OMP_CLAUSE_MAP_MAYBE_ZERO_LENGTH_ARRAY_SECTION (c) = 1;
 	}
       if (TREE_CODE (TREE_TYPE (orig_decl)) == REFERENCE_TYPE
 	  && (GFC_DECL_GET_SCALAR_POINTER (orig_decl)
diff --git a/gcc/testsuite/gfortran.dg/goacc/assumed-size.f90 b/gcc/testsuite/gfortran.dg/goacc/assumed-size.f90
index 4fced2e70c9..12f44c4743a 100644
--- a/gcc/testsuite/gfortran.dg/goacc/assumed-size.f90
+++ b/gcc/testsuite/gfortran.dg/goacc/assumed-size.f90
@@ -4,7 +4,8 @@ 
 ! exit data, respectively.
 
 ! This does not appear to be supported by the OpenACC standard as of version
-! 3.0.  Check for an appropriate error message.
+! 3.0.  There is however real-world code that relies on this working, so we
+! make an attempt to support it.
 
 program test
   implicit none
@@ -26,7 +27,6 @@  subroutine dtest (a, n)
   !$acc enter data copyin(a(1:n))
 
   !$acc parallel loop
-! { dg-error {implicit mapping of assumed size array 'a'} "" { target *-*-* } .-1 }
   do i = 1, n
      a(i) = i
   end do
diff --git a/libgomp/testsuite/libgomp.oacc-fortran/nonlexical-assumed-size-1.f90 b/libgomp/testsuite/libgomp.oacc-fortran/nonlexical-assumed-size-1.f90
new file mode 100644
index 00000000000..4b61e1cee9b
--- /dev/null
+++ b/libgomp/testsuite/libgomp.oacc-fortran/nonlexical-assumed-size-1.f90
@@ -0,0 +1,28 @@ 
+! { dg-do run }
+
+program p
+implicit none
+integer :: myarr(10)
+
+myarr = 0
+
+call subr(myarr)
+
+if (myarr(5).ne.5) stop 1
+
+contains
+
+subroutine subr(arr)
+implicit none
+integer :: arr(*)
+
+!$acc enter data copyin(arr(1:10))
+
+!$acc serial
+arr(5) = 5
+!$acc end serial
+
+!$acc exit data copyout(arr(1:10))
+
+end subroutine subr
+end program p
diff --git a/libgomp/testsuite/libgomp.oacc-fortran/nonlexical-assumed-size-2.f90 b/libgomp/testsuite/libgomp.oacc-fortran/nonlexical-assumed-size-2.f90
new file mode 100644
index 00000000000..daf7089915f
--- /dev/null
+++ b/libgomp/testsuite/libgomp.oacc-fortran/nonlexical-assumed-size-2.f90
@@ -0,0 +1,40 @@ 
+! { dg-do run }
+
+program p
+implicit none
+integer :: myarr(10)
+
+myarr = 0
+
+call subr(myarr)
+
+if (myarr(5).ne.5) stop 1
+
+contains
+
+subroutine subr(arr)
+implicit none
+integer :: arr(*)
+
+! At first glance, it might not be obvious how this works.  The "enter data"
+! and "exit data" operations expand to a pair of mapping nodes for OpenACC,
+! GOMP_MAP_{TO/FROM} and GOMP_MAP_POINTER.  The former maps the array data,
+! and the latter creates a separate mapping on the target for the pointer
+! itself with a bias so it represents the "zeroth" element.
+
+!$acc enter data copyin(arr(2:8))
+
+! ...then this implicit mapping creates a zero-length array section
+! (GOMP_MAP_ZERO_LEN_ARRAY_SECTION) followed by another GOMP_MAP_POINTER for
+! 'arr'.  But now that pointer is already "present" on the target, so is not
+! overwritten.
+
+!$acc serial
+! This access is then done via the on-target pointer.
+arr(5) = 5
+!$acc end serial
+
+!$acc exit data copyout(arr(2:8))
+
+end subroutine subr
+end program p