[Flang][openmp][5/5] Make dist_schedule clause part of OmpClause

After discussion in `D93482` we found that the some of the clauses were not
following the common OmpClause convention.

The benefits of using OmpClause:
- Functionalities from structure checker are mostly aligned to work with
  `llvm::omp::Clause`.
- The unparsing as well can take advantage.
- Homogeneity with OpenACC and rest of the clauses in OpenMP.
- Could even generate the parser with TableGen, when there is homogeneity.
- It becomes confusing when to use `flangClass` and `flangClassValue` inside
  TableGen, if incase we generate parser using TableGen we could have only a
  single `let expression`.

This patch makes `OmpDistScheduleClause` clause part of `OmpClause`.
The unparse function for `OmpDistScheduleClause` is adapted since the keyword
and parenthesis are issued by the corresponding unparse function for
`parser::OmpClause::DistSchedule`.

Reviewed By: clementval, kiranktp

Differential Revision: https://reviews.llvm.org/D93644

flang/include/flang/Parser/dump-parse-tree.h

@@ -485,7 +485,6 @@ public:
   NODE_ENUM(OmpDependenceType, Type)
   NODE(parser, OmpDependSinkVec)
   NODE(parser, OmpDependSinkVecLength)
-  NODE(parser, OmpDistScheduleClause)
   NODE(parser, OmpEndAtomic)
   NODE(parser, OmpEndBlockDirective)
   NODE(parser, OmpEndCriticalDirective)

flang/include/flang/Parser/parse-tree.h

@@ -3456,10 +3456,6 @@ struct OmpDependClause {
   std::variant<Source, Sink, InOut> u;
 };
 
-// dist_schedule clause does not fit in generic clause class for tablegen.
-// Therefore it is declared separatly here.
-WRAPPER_CLASS(OmpDistScheduleClause, std::optional<ScalarIntExpr>);
-
 // OpenMP Clauses
 struct OmpClause {
   UNION_CLASS_BOILERPLATE(OmpClause);

flang/lib/Parser/openmp-parsers.cpp

@@ -176,7 +176,7 @@ TYPE_PARSER(
     "DEVICE" >> construct<OmpClause>(construct<OmpClause::Device>(
                     parenthesized(scalarIntExpr))) ||
     "DIST_SCHEDULE" >>
-        construct<OmpClause>(construct<OmpDistScheduleClause>(
+        construct<OmpClause>(construct<OmpClause::DistSchedule>(
             parenthesized("STATIC" >> maybe("," >> scalarIntExpr)))) ||
     "FINAL" >> construct<OmpClause>(construct<OmpClause::Final>(
                    parenthesized(scalarLogicalExpr))) ||

flang/lib/Parser/unparse.cpp

@@ -2065,11 +2065,6 @@ public:
         std::get<std::optional<OmpDefaultmapClause::VariableCategory>>(x.t));
     Word(")");
   }
-  void Unparse(const OmpDistScheduleClause &x) {
-    Word("DIST_SCHEDULE(STATIC");
-    Walk(", ", x.v);
-    Put(")");
-  }
 #define GEN_FLANG_CLAUSE_UNPARSE
 #include "llvm/Frontend/OpenMP/OMP.inc"
   void Unparse(const OmpLoopDirective &x) {

flang/lib/Semantics/check-omp-structure.cpp

@@ -430,6 +430,7 @@ CHECK_SIMPLE_CLAUSE(Release, OMPC_release)
 CHECK_SIMPLE_CLAUSE(Relaxed, OMPC_relaxed)
 CHECK_SIMPLE_CLAUSE(Hint, OMPC_hint)
 CHECK_SIMPLE_CLAUSE(ProcBind, OMPC_proc_bind)
+CHECK_SIMPLE_CLAUSE(DistSchedule, OMPC_dist_schedule)
 
 CHECK_REQ_SCALAR_INT_CLAUSE(Allocator, OMPC_allocator)
 CHECK_REQ_SCALAR_INT_CLAUSE(Grainsize, OMPC_grainsize)
@@ -493,7 +494,6 @@ void OmpStructureChecker::CheckIsVarPartOfAnotherVar(
   }
 }
 // Following clauses have a seperate node in parse-tree.h.
-CHECK_SIMPLE_PARSER_CLAUSE(OmpDistScheduleClause, OMPC_dist_schedule)
 CHECK_SIMPLE_PARSER_CLAUSE(OmpReductionClause, OMPC_reduction)
 // Atomic-clause
 CHECK_SIMPLE_PARSER_CLAUSE(OmpAtomicRead, OMPC_read)

flang/lib/Semantics/check-omp-structure.h

@@ -139,6 +139,7 @@ public:
   void Enter(const parser::OmpClause::Copyprivate &);
   void Enter(const parser::OmpClause::Default &);
   void Enter(const parser::OmpClause::Device &);
+  void Enter(const parser::OmpClause::DistSchedule &);
   void Enter(const parser::OmpClause::Final &);
   void Enter(const parser::OmpClause::Firstprivate &);
   void Enter(const parser::OmpClause::From &);
@@ -179,7 +180,6 @@ public:
   void Enter(const parser::OmpAlignedClause &);
   void Enter(const parser::OmpDefaultmapClause &);
   void Enter(const parser::OmpDependClause &);
-  void Enter(const parser::OmpDistScheduleClause &);
   void Enter(const parser::OmpIfClause &);
   void Enter(const parser::OmpLinearClause &);
   void Enter(const parser::OmpMapClause &);

llvm/include/llvm/Frontend/OpenMP/OMP.td

@@ -204,7 +204,6 @@ def OMPC_Hint : Clause<"hint"> {
 }
 def OMPC_DistSchedule : Clause<"dist_schedule"> {
   let clangClass = "OMPDistScheduleClause";
-  let flangClass = "OmpDistScheduleClause";
   let flangClassValue = "ScalarIntExpr";
   let isValueOptional = true;
 }