[WIP][Flang][OpenMP] Add support for integer subtraction reduction in worksharing-loop

[DylanFleming-arm]

Summary

Adds support for reduction of subtraction.

WIP: Currently, MLIR outputs from this patch appear correct
but when compiled and ran the wrong result is given.

[DylanFleming-arm]

Feature fully deprecated in D132060

flang/lib/Lower/OpenMP.cpp

 }
 
 /// This function returns the identity value of the operator \p reductionOpName.
 /// For example:
 ///    0 + x = x,
 ///    1 * x = x
 static int getOperationIdentity(llvm::StringRef reductionOpName,
                                 mlir::Location loc) {
-  if (reductionOpName.contains("add"))
+  if (reductionOpName.contains("add") || reductionOpName.contains("subtract"))
     return 0;
   else if (reductionOpName.contains("multiply"))
     return 1;
   TODO(loc, "Reduction of some intrinsic operators is not supported");
 }
 
 static Value getReductionInitValue(mlir::Location loc, mlir::Type type,
                                    llvm::StringRef reductionOpName,
static omp::ReductionDeclareOp createReductionDecl(
   mlir::Value op1 = decl.reductionRegion().front().getArgument(0);
   mlir::Value op2 = decl.reductionRegion().front().getArgument(1);
 
   Value res;
   switch (intrinsicOp) {
   case Fortran::parser::DefinedOperator::IntrinsicOperator::Add:
     res = builder.create<mlir::arith::AddIOp>(loc, op1, op2);
     break;
+  case Fortran::parser::DefinedOperator::IntrinsicOperator::Subtract:
+    res = builder.create<mlir::arith::SubIOp>(loc, op1, op2);
+    break;
   case Fortran::parser::DefinedOperator::IntrinsicOperator::Multiply:
     res = builder.create<mlir::arith::MulIOp>(loc, op1, op2);
     break;
   default:
     TODO(loc, "Reduction of some intrinsic operators is not supported");
   }
 
   builder.create<omp::YieldOp>(loc, res);
static std::string getReductionName(
     Fortran::parser::DefinedOperator::IntrinsicOperator intrinsicOp,
     mlir::Type ty) {
   std::string reductionName;
 
   switch (intrinsicOp) {
   case Fortran::parser::DefinedOperator::IntrinsicOperator::Add:
     reductionName = "add_reduction";
     break;
+  case Fortran::parser::DefinedOperator::IntrinsicOperator::Subtract:
+    reductionName = "subtract_reduction";
+    break;
   case Fortran::parser::DefinedOperator::IntrinsicOperator::Multiply:
     reductionName = "multiply_reduction";
     break;
   default:
     reductionName = "other_reduction";
     break;
   }
 
if (const auto &scheduleClause =
           std::get<Fortran::parser::OmpObjectList>(reductionClause->v.t)};
       if (const auto &redDefinedOp =
               std::get_if<Fortran::parser::DefinedOperator>(&redOperator.u)) {
         const auto &intrinsicOp{
             std::get<Fortran::parser::DefinedOperator::IntrinsicOperator>(
                 redDefinedOp->u)};
         switch (intrinsicOp) {
         case Fortran::parser::DefinedOperator::IntrinsicOperator::Add:
+        case Fortran::parser::DefinedOperator::IntrinsicOperator::Subtract:
         case Fortran::parser::DefinedOperator::IntrinsicOperator::Multiply:
           break;
 
         default:
           TODO(currentLocation,
                "Reduction of some intrinsic operators is not supported");
           break;
         }
if (const auto &reductionClause =
       if (auto reductionOp =
               std::get_if<Fortran::parser::DefinedOperator>(&redOperator.u)) {
         const auto &intrinsicOp{
             std::get<Fortran::parser::DefinedOperator::IntrinsicOperator>(
                 reductionOp->u)};
 
         switch (intrinsicOp) {
         case Fortran::parser::DefinedOperator::IntrinsicOperator::Add:
+        case Fortran::parser::DefinedOperator::IntrinsicOperator::Subtract:
         case Fortran::parser::DefinedOperator::IntrinsicOperator::Multiply:
           break;
         default:
           continue;
         }
         for (const auto &ompObject : objectList.v) {
           if (const auto *name{
                   Fortran::parser::Unwrap<Fortran::parser::Name>(ompObject)}) {