[Flang][openmp][1/5] Make Allocate 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 `allocate` clause part of `OmpClause`.The unparse function for
`OmpAllocateClause` is adapted since the keyword and parenthesis are issued by
the corresponding unparse function for `parser::OmpClause::Allocate`.

Reviewed By: clementval

Differential Revision: https://reviews.llvm.org/D93640

flang/lib/Parser/openmp-parsers.cpp

@@ -157,8 +157,8 @@ TYPE_PARSER(
     "ACQ_REL" >> construct<OmpClause>(construct<OmpClause::AcqRel>()) ||
     "ALIGNED" >>
         construct<OmpClause>(parenthesized(Parser<OmpAlignedClause>{})) ||
-    "ALLOCATE" >>
-        construct<OmpClause>(parenthesized(Parser<OmpAllocateClause>{})) ||
+    "ALLOCATE" >> construct<OmpClause>(construct<OmpClause::Allocate>(
+                      parenthesized(Parser<OmpAllocateClause>{}))) ||
     "ALLOCATOR" >> construct<OmpClause>(construct<OmpClause::Allocator>(
                        parenthesized(scalarIntExpr))) ||
     "COLLAPSE" >> construct<OmpClause>(construct<OmpClause::Collapse>(

flang/lib/Parser/unparse.cpp

@@ -2020,10 +2020,9 @@ public:
     Put(")");
   }
   void Unparse(const OmpAllocateClause &x) {
-    Word("ALLOCATE(");
-    Walk(std::get<std::optional<OmpAllocateClause::Allocator>>(x.t), ":");
+    Walk(std::get<std::optional<OmpAllocateClause::Allocator>>(x.t));
+    Put(":");
     Walk(std::get<OmpObjectList>(x.t));
-    Put(")");
   }
   void Unparse(const OmpDependSinkVecLength &x) {
     Walk(std::get<DefinedOperator>(x.t));

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

@@ -403,6 +403,7 @@ void OmpStructureChecker::Enter(const parser::OmpClause &x) {
 
 // Following clauses do not have a seperate node in parse-tree.h.
 // They fall under 'struct OmpClause' in parse-tree.h.
+CHECK_SIMPLE_CLAUSE(Allocate, OMPC_allocate)
 CHECK_SIMPLE_CLAUSE(Copyin, OMPC_copyin)
 CHECK_SIMPLE_CLAUSE(Copyprivate, OMPC_copyprivate)
 CHECK_SIMPLE_CLAUSE(Device, OMPC_device)
@@ -489,7 +490,6 @@ void OmpStructureChecker::CheckIsVarPartOfAnotherVar(
   }
 }
 // Following clauses have a seperate node in parse-tree.h.
-CHECK_SIMPLE_PARSER_CLAUSE(OmpAllocateClause, OMPC_allocate)
 CHECK_SIMPLE_PARSER_CLAUSE(OmpDefaultClause, OMPC_default)
 CHECK_SIMPLE_PARSER_CLAUSE(OmpDistScheduleClause, OMPC_dist_schedule)
 CHECK_SIMPLE_PARSER_CLAUSE(OmpNowait, OMPC_nowait)

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

@@ -127,6 +127,7 @@ public:
   void Leave(const parser::OmpClauseList &);
   void Enter(const parser::OmpClause &);
   void Enter(const parser::OmpNowait &);
+  void Enter(const parser::OmpClause::Allocate &);
   void Enter(const parser::OmpClause::Allocator &);
   void Enter(const parser::OmpClause::Inbranch &);
   void Enter(const parser::OmpClause::Mergeable &);
@@ -174,7 +175,6 @@ public:
   void Enter(const parser::OmpAtomicCapture &);
   void Leave(const parser::OmpAtomic &);
   void Enter(const parser::OmpAlignedClause &);
-  void Enter(const parser::OmpAllocateClause &);
   void Enter(const parser::OmpDefaultClause &);
   void Enter(const parser::OmpDefaultmapClause &);
   void Enter(const parser::OmpDependClause &);

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

@@ -254,7 +254,7 @@ def OMPC_AtomicDefaultMemOrder : Clause<"atomic_default_mem_order"> {
 }
 def OMPC_Allocate : Clause<"allocate"> {
   let clangClass = "OMPAllocateClause";
-  let flangClass = "OmpAllocateClause";
+  let flangClassValue = "OmpAllocateClause";
 }
 def OMPC_NonTemporal : Clause<"nontemporal"> {
   let clangClass = "OMPNontemporalClause";