[gcc/devel/omp/gcc-16] openmp: Disable strided target updates when iterators are used

https://gcc.gnu.org/g:f9b688be25d266f85a9eb745954998346685f361

commit f9b688be25d266f85a9eb745954998346685f361
Author: Kwok Cheung Yeung <[email protected]>
Date:   Thu Apr 23 22:34:40 2026 +0000

    openmp: Disable strided target updates when iterators are used
    
    Non-contiguous target updates result in the new strided target updates code
    being used, resulting in new clauses such as GOMP_MAP_GRID_DIM,
    GOMP_MAP_GRID_STRIDE etc. These are not currently supported in conjunction
    with iterators, so this code-path is disabled when used together with
    iterators.
    
    The older target updates supports non-contiguous updates as long as a stride
    is not applied.
    
    gcc/c/
    
            * c-typeck.cc (handle_omp_array_sections): Add extra argument.  Set
            argument to true if array section has a stride that is not one.
            (c_finish_omp_clauses): Disable strided updates when iterators are
            used in the clause.  Emit sorry if strided.
    
    gcc/cp/
    
            * semantics.cc (handle_omp_array_sections): Add extra argument.  Set
            argument to true if array section has a stride that is not one.
            (finish_omp_clauses): Disable strided updates when iterators are
            used in the clause.  Emit sorry if strided.
    
    gcc/fortran/
    
            * trans-openmp.cc (gfc_trans_omp_clauses): Disable strided updates
            when iterators are used in the clause.

Diff:
---
 gcc/c/c-typeck.cc           | 17 ++++++++++++++---
 gcc/cp/semantics.cc         | 18 ++++++++++++++----
 gcc/fortran/trans-openmp.cc |  3 +++
 3 files changed, 31 insertions(+), 7 deletions(-)

diff --git a/gcc/c/c-typeck.cc b/gcc/c/c-typeck.cc
index 9b1967ef9262..672f55c2f996 100644
--- a/gcc/c/c-typeck.cc
+++ b/gcc/c/c-typeck.cc
@@ -16310,7 +16310,7 @@ omp_array_section_low_bound (location_t loc, tree node)
 
 static bool
 handle_omp_array_sections (tree *pc, tree **pnext, enum c_omp_region_type ort,
-			   int *discontiguous)
+			   int *discontiguous, bool *strided = NULL)
 {
   tree c = *pc;
   bool maybe_zero_len = false;
@@ -16399,6 +16399,8 @@ handle_omp_array_sections (tree *pc, tree **pnext, enum c_omp_region_type ort,
 
 	  if (stride == NULL_TREE)
 	    stride = size_one_node;
+	  if (strided && !integer_onep (stride))
+	    *strided = true;
 	  if (discontiguous && *discontiguous)
 	    {
 	      /* This condition is similar to the error check below, but
@@ -17889,13 +17891,22 @@ c_finish_omp_clauses (tree clauses, enum c_omp_region_type ort)
 		grp_sentinel = OMP_CLAUSE_CHAIN (c);
 
 		tree *pnext = NULL;
+		/* FIXME: Strided target updates not supported together with
+		   iterators yet.  */
 		int discontiguous
 		  = (OMP_CLAUSE_CODE (c) == OMP_CLAUSE_TO
-		     || OMP_CLAUSE_CODE (c) == OMP_CLAUSE_FROM);
-		if (handle_omp_array_sections (pc, &pnext, ort, &discontiguous))
+		     || OMP_CLAUSE_CODE (c) == OMP_CLAUSE_FROM)
+		    && !OMP_CLAUSE_ITERATORS (c);
+		bool strided = false;
+		if (handle_omp_array_sections (pc, &pnext, ort, &discontiguous,
+					       &strided))
 		  remove = true;
 		else
 		  {
+		    if ((OMP_CLAUSE_CODE (c) == OMP_CLAUSE_TO
+			 || OMP_CLAUSE_CODE (c) == OMP_CLAUSE_FROM)
+			&& OMP_CLAUSE_ITERATORS (c) && strided)
+		      sorry ("strided target updates with iterators");
 		    c = *pc;
 		    t = OMP_CLAUSE_DECL (c);
 		    if (!omp_mappable_type (TREE_TYPE (t)))
diff --git a/gcc/cp/semantics.cc b/gcc/cp/semantics.cc
index 50e4493bcf4b..24e3bd9b82d7 100644
--- a/gcc/cp/semantics.cc
+++ b/gcc/cp/semantics.cc
@@ -6515,7 +6515,7 @@ omp_array_section_low_bound (location_t loc, tree node)
 
 static bool
 handle_omp_array_sections (tree *pc, tree **pnext, enum c_omp_region_type ort,
-			   int *discontiguous)
+			   int *discontiguous, bool *strided = NULL)
 {
   tree c = *pc;
   bool maybe_zero_len = false;
@@ -6609,6 +6609,8 @@ handle_omp_array_sections (tree *pc, tree **pnext, enum c_omp_region_type ort,
 
 	  if (stride == NULL_TREE)
 	    stride = size_one_node;
+	  if (strided && !integer_onep (stride))
+	    *strided = true;
 	  if (discontiguous && *discontiguous)
 	    {
 	      /* This condition is similar to the error check below, but
@@ -9546,15 +9548,23 @@ finish_omp_clauses (tree clauses, enum c_omp_region_type ort)
 	      {
 		grp_start_p = pc;
 		grp_sentinel = OMP_CLAUSE_CHAIN (c);
-
+		/* FIXME: Strided target updates not supported together with
+		   iterators yet.  */
 		int discontiguous
 		  = (OMP_CLAUSE_CODE (c) == OMP_CLAUSE_TO
-		     || OMP_CLAUSE_CODE (c) == OMP_CLAUSE_FROM);
+		     || OMP_CLAUSE_CODE (c) == OMP_CLAUSE_FROM)
+		    && !OMP_CLAUSE_ITERATORS (c);
+		bool strided = false;
 		tree *pnext = NULL;
-		if (handle_omp_array_sections (pc, &pnext, ort, &discontiguous))
+		if (handle_omp_array_sections (pc, &pnext, ort, &discontiguous,
+					       &strided))
 		  remove = true;
 		else
 		  {
+		    if ((OMP_CLAUSE_CODE (c) == OMP_CLAUSE_TO
+			 || OMP_CLAUSE_CODE (c) == OMP_CLAUSE_FROM)
+			&& OMP_CLAUSE_ITERATORS (c) && strided)
+		      sorry ("strided target updates with iterators");
 		    /* We might have replaced the clause, so refresh C.  */
 		    c = *pc;
 		    t = OMP_CLAUSE_DECL (c);
diff --git a/gcc/fortran/trans-openmp.cc b/gcc/fortran/trans-openmp.cc
index 743e63767944..d2895b05e9ec 100644
--- a/gcc/fortran/trans-openmp.cc
+++ b/gcc/fortran/trans-openmp.cc
@@ -5852,7 +5852,10 @@ gfc_trans_omp_clauses (stmtblock_t *block, gfc_omp_clauses *clauses,
 		  gcc_unreachable ();
 		}
 
+	      /* FIXME: Currently no support for strided target updates with
+		 iterators.  */
 	      if ((list == OMP_LIST_TO || list == OMP_LIST_FROM)
+		  && !iterator
 		  && (!n->expr
 		       || (n->expr
 			   && n->expr->ref