(closes #3411) Remove OpenMP SUB reduction operator (use ADD instead)

changelog

@@ -1,4 +1,7 @@
-   9) PR #3406 for # 3406. Fix issue with comment before a subroutine that
+   10) PR #3413 for #3411. Remove OpenMP SUB reduction operator and relpace
+   with ADD as is required by OpenMP 5.2.
+
+   9) PR #3406 for #3406. Fix issue with comment before a subroutine that
    turns into a CodeBlock.
 
    8) PR #3371 towards #3012. Add workaround to bypass psyclonefc fixed-from

src/psyclone/psyir/backend/fortran.py

@@ -1636,7 +1636,6 @@ def operatorclause_node(self, node):
             OMPDependClause.DependClauseTypes.OUT: "out",
             OMPDependClause.DependClauseTypes.INOUT: "inout",
             OMPReductionClause.ReductionClauseTypes.ADD: "+",
-            OMPReductionClause.ReductionClauseTypes.SUB: "-",
             OMPReductionClause.ReductionClauseTypes.MUL: "*",
             OMPReductionClause.ReductionClauseTypes.AND: ".AND.",
             OMPReductionClause.ReductionClauseTypes.OR: ".OR.",

src/psyclone/psyir/nodes/omp_clauses.py

@@ -508,19 +508,18 @@ class ReductionClauseTypes(Enum):
         supported in PSyclone.'''
         # Arithmetic operators
         ADD = 0
-        SUB = 1
-        MUL = 2
+        MUL = 1
         # Logical operators
-        AND = 3
-        OR = 4
-        EQV = 5  # Fortran specific
-        NEQV = 6  # Fortran specific
+        AND = 2
+        OR = 3
+        EQV = 4  # Fortran specific
+        NEQV = 5  # Fortran specific
         # Intrinsic procedures
-        MAX = 7
-        MIN = 8
-        IAND = 9
-        IOR = 10
-        IEOR = 11
+        MAX = 6
+        MIN = 7
+        IAND = 8
+        IOR = 9
+        IEOR = 10
 
     def __init__(self, operator: ReductionClauseTypes, **kwargs):
         if not isinstance(operator, OMPReductionClause.ReductionClauseTypes):

src/psyclone/psyir/nodes/omp_directives.py

@@ -89,8 +89,9 @@
 MAP_REDUCTION_OP_TO_OMP = {
     BinaryOperation.Operator.ADD:
         OMPReductionClause.ReductionClauseTypes.ADD,
+    # From OpenMP 5.2 the - reduction is not supported, use + instead
     BinaryOperation.Operator.SUB:
-        OMPReductionClause.ReductionClauseTypes.SUB,
+        OMPReductionClause.ReductionClauseTypes.ADD,
     BinaryOperation.Operator.MUL:
         OMPReductionClause.ReductionClauseTypes.MUL,
     BinaryOperation.Operator.AND:

src/psyclone/tests/psyir/nodes/omp_directives_test.py

@@ -4871,6 +4871,9 @@ def test_reduction_arith_ops(op, fortran_reader, fortran_writer):
     loop = psyir.walk(Loop)[0]
     omplooptrans.apply(loop, enable_reductions=True)
     output = fortran_writer(psyir)
+    # The + and - operators are equivalent, from OpenMP 5.2 the - is deprecated
+    if op == "-":
+        op = "+"
     assert f"reduction({op}: acc)" in output