[gcc r16-6513] openmp: Improve Fortran Diagnostics for Linear Clause

[Gio T]

https://gcc.gnu.org/g:cdb15b390035fc4843e11363bcc4e0eff419d6a3

commit r16-6513-gcdb15b390035fc4843e11363bcc4e0eff419d6a3
Author: supers1ngular <supers1ngular@baylibre.com>
Date:   Mon Jan 5 17:09:02 2026 -0800

    openmp: Improve Fortran Diagnostics for Linear Clause
    
    This patch improves diagnostics for the linear clause,
    providing a more accurate and intuitive recommendation
    for remediation if the deprecated syntax is used.
    Additionally updates the relevant test to reflect the
    changed verbiage of the warning.
    
    gcc/fortran/ChangeLog:
    
            * openmp.cc (gfc_match_omp_clauses): New diagnostic logic.
    
    libgomp/ChangeLog:
    
            * testsuite/libgomp.fortran/pr84418-1.f90: Fix verbiage of
            dg-warning to reflect updated warning.

Diff:
---
 gcc/fortran/openmp.cc                           | 51 ++++++++++++++++++++++---
 libgomp/testsuite/libgomp.fortran/pr84418-1.f90 |  3 +-
 2 files changed, 48 insertions(+), 6 deletions(-)

diff --git a/gcc/fortran/openmp.cc b/gcc/fortran/openmp.cc
index dddb42f2d998..5823ac41fa51 100644
--- a/gcc/fortran/openmp.cc
+++ b/gcc/fortran/openmp.cc
@@ -3481,11 +3481,6 @@ gfc_match_omp_clauses (gfc_omp_clauses **cp, const omp_mask mask,
 		  gfc_current_locus = old_loc;
 		  break;
 		}
-	      if (old_linear_modifier)
-		gfc_warning (OPT_Wdeprecated_openmp,
-			     "Specification of the list items as arguments to "
-			     "the modifiers at %L is deprecated since "
-			     "OpenMP 5.2", &saved_loc);
 	      if (linear_op != OMP_LINEAR_DEFAULT)
 		{
 		  if (gfc_match (" :") == MATCH_YES)
@@ -3509,6 +3504,52 @@ gfc_match_omp_clauses (gfc_omp_clauses **cp, const omp_mask mask,
 		      goto error;
 		    }
 		}
+	      if (old_linear_modifier)
+		{
+		  char var_names[512]{};
+		  int count, offset = 0;
+		  for (gfc_omp_namelist *n = *head; n; n = n->next)
+		    {
+		      if (!n->next)
+			count = snprintf (var_names + offset,
+					  sizeof (var_names) - offset,
+					  "%s", n->sym->name);
+		      else
+			count = snprintf (var_names + offset,
+					  sizeof (var_names) - offset,
+					  "%s, ", n->sym->name);
+		      if (count < 0 || count >= ((int)sizeof (var_names))
+						- offset)
+			{
+			  snprintf (var_names, 512, "%s, ..., ",
+				    (*head)->sym->name);
+			  while (n->next)
+			    n = n->next;
+			  offset = strlen (var_names);
+			  snprintf (var_names + offset,
+				    sizeof (var_names) - offset,
+				    "%s", n->sym->name);
+			  break;
+			}
+		      offset += count;
+		    }
+		  char *var_names_for_warn = var_names;
+		  const char *op_name;
+		  switch (linear_op)
+		    {
+		      case OMP_LINEAR_REF: op_name = "ref"; break;
+		      case OMP_LINEAR_VAL: op_name = "val"; break;
+		      case OMP_LINEAR_UVAL: op_name = "uval"; break;
+		      default: gcc_unreachable ();
+		    }
+		  gfc_warning (OPT_Wdeprecated_openmp,
+			       "Specification of the list items as "
+			       "arguments to the modifiers at %L is "
+			       "deprecated; since OpenMP 5.2, use "
+			       "%<linear(%s : %s%s)%>", &saved_loc,
+			       var_names_for_warn, op_name,
+			       step == nullptr ? "" : ", step(...)");
+		}
 	      else if (end_colon)
 		{
 		  bool has_error = false;
diff --git a/libgomp/testsuite/libgomp.fortran/pr84418-1.f90 b/libgomp/testsuite/libgomp.fortran/pr84418-1.f90
index 65dae5d0b0b0..b86dfe5d92ad 100644
--- a/libgomp/testsuite/libgomp.fortran/pr84418-1.f90
+++ b/libgomp/testsuite/libgomp.fortran/pr84418-1.f90
@@ -3,6 +3,7 @@
 ! { dg-options "-fno-inline" }
 ! { dg-additional-options "-msse2" { target sse2_runtime } }
 ! { dg-additional-options "-mavx" { target avx_runtime } }
+! { dg-warning "Specification of the list items as arguments to the modifiers at \\(1\\) is deprecated; since OpenMP 5.2, use 'linear\\(x, y : ref\\)' \\\[-Wdeprecated-openmp\\\]" "" { target *-*-* } 24 }
 
   real :: a(1024), b(1024), c(1024)
   integer :: i
@@ -20,7 +21,7 @@
 contains
   real function foo (x, y)
     real :: x, y
-    !$omp declare simd linear (ref (x, y)) ! { dg-warning "Specification of the list items as arguments to the modifiers at \\(1\\) is deprecated since OpenMP 5.2 \\\[-Wdeprecated-openmp\\\]" }
+    !$omp declare simd linear (ref (x, y))
     foo = x + y
   end function
 end