[flang][openacc] Remove single reduction clause limitation

[razvanlupusoru]

Summary

The constraint that a single reduction clause is allowed is actually
not valid as per OpenACC specification. Multiple reduction clauses
are allowed, especially since reduction clauses can have different
reduction operators.

[razvanlupusoru]

I am adding tests as part of this: https://reviews.llvm.org/D151955

But I separated this change since it is not in the flang folder. I did keep [flang] in the title, just as was done with the commits when this file was first created.

[vzakhari]

LGTM. Thank you!

llvm/include/llvm/Frontend/OpenACC/ACC.td

let allowedClauses = [
     VersionedClause<ACCC_Copyout>,
     VersionedClause<ACCC_Create>,
     VersionedClause<ACCC_DevicePtr>,
     VersionedClause<ACCC_DeviceType>,
     VersionedClause<ACCC_NoCreate>,
     VersionedClause<ACCC_Present>,
     VersionedClause<ACCC_Private>,
     VersionedClause<ACCC_FirstPrivate>,
+    VersionedClause<ACCC_Reduction>,
     VersionedClause<ACCC_Wait>
   ];
   let allowedOnceClauses = [
     VersionedClause<ACCC_Async>,
     VersionedClause<ACCC_Default>,
     VersionedClause<ACCC_If>,
     VersionedClause<ACCC_NumGangs>,
     VersionedClause<ACCC_NumWorkers>,
-    VersionedClause<ACCC_Reduction>,
     VersionedClause<ACCC_Self>,
     VersionedClause<ACCC_VectorLength>
   ];
 }
 
 // 2.5.2
 def ACC_Serial : Directive<"serial"> {
   // Spec line 950-951: clause is as for the parallel construct except that the
   // num_gangs, num_workers, and vector_length clauses are not permitted.
   let allowedClauses = [
     VersionedClause<ACCC_Attach>,
     VersionedClause<ACCC_Copy>,
     VersionedClause<ACCC_Copyin>,
     VersionedClause<ACCC_Copyout>,
     VersionedClause<ACCC_Create>,
     VersionedClause<ACCC_DevicePtr>,
     VersionedClause<ACCC_DeviceType>,
     VersionedClause<ACCC_NoCreate>,
     VersionedClause<ACCC_Present>,
     VersionedClause<ACCC_Private>,
     VersionedClause<ACCC_FirstPrivate>,
+    VersionedClause<ACCC_Reduction>,
     VersionedClause<ACCC_Wait>
   ];
   let allowedOnceClauses = [
     VersionedClause<ACCC_Async>,
     VersionedClause<ACCC_Default>,
     VersionedClause<ACCC_If>,
-    VersionedClause<ACCC_Reduction>,
     VersionedClause<ACCC_Self>
   ];
 }
 
 // 2.9
 def ACC_Loop : Directive<"loop"> {
   let allowedClauses = [
     VersionedClause<ACCC_DeviceType>,
-    VersionedClause<ACCC_Private>
+    VersionedClause<ACCC_Private>,
+    VersionedClause<ACCC_Reduction>
   ];
   let allowedOnceClauses = [
     VersionedClause<ACCC_Collapse>,
     VersionedClause<ACCC_Gang>,
-    VersionedClause<ACCC_Reduction>,
     VersionedClause<ACCC_Tile>,
     VersionedClause<ACCC_Vector>,
     VersionedClause<ACCC_Worker>
   ];
   let allowedExclusiveClauses = [
     VersionedClause<ACCC_Auto>,
     VersionedClause<ACCC_Independent>,
     VersionedClause<ACCC_Seq>
let allowedClauses = [
     VersionedClause<ACCC_Copy>,
     VersionedClause<ACCC_Copyin>,
     VersionedClause<ACCC_Copyout>,
     VersionedClause<ACCC_Create>,
     VersionedClause<ACCC_DeviceType>,
     VersionedClause<ACCC_NoCreate>,
     VersionedClause<ACCC_Present>,
     VersionedClause<ACCC_Private>,
+    VersionedClause<ACCC_Reduction>,
     VersionedClause<ACCC_DevicePtr>,
     VersionedClause<ACCC_Attach>,
     VersionedClause<ACCC_Wait>
   ];
   let allowedOnceClauses = [
     VersionedClause<ACCC_Async>,
     VersionedClause<ACCC_Collapse>,
     VersionedClause<ACCC_Default>,
     VersionedClause<ACCC_Gang>,
     VersionedClause<ACCC_If>,
     VersionedClause<ACCC_NumGangs>,
     VersionedClause<ACCC_NumWorkers>,
-    VersionedClause<ACCC_Reduction>,
     VersionedClause<ACCC_Self>,
     VersionedClause<ACCC_Tile>,
     VersionedClause<ACCC_Vector>,
     VersionedClause<ACCC_VectorLength>,
     VersionedClause<ACCC_Worker>
   ];
   let allowedExclusiveClauses = [
     VersionedClause<ACCC_Auto>,
let allowedClauses = [
     VersionedClause<ACCC_Copyout>,
     VersionedClause<ACCC_Create>,
     VersionedClause<ACCC_DevicePtr>,
     VersionedClause<ACCC_DeviceType>,
     VersionedClause<ACCC_FirstPrivate>,
     VersionedClause<ACCC_NoCreate>,
     VersionedClause<ACCC_Present>,
     VersionedClause<ACCC_Private>,
+    VersionedClause<ACCC_Reduction>,
     VersionedClause<ACCC_Tile>,
     VersionedClause<ACCC_Wait>
   ];
   let allowedOnceClauses = [
     VersionedClause<ACCC_Async>,
     VersionedClause<ACCC_Collapse>,
     VersionedClause<ACCC_Default>,
     VersionedClause<ACCC_Gang>,
     VersionedClause<ACCC_If>,
     VersionedClause<ACCC_NumGangs>,
     VersionedClause<ACCC_NumWorkers>,
-    VersionedClause<ACCC_Reduction>,
     VersionedClause<ACCC_Self>,
     VersionedClause<ACCC_Vector>,
     VersionedClause<ACCC_VectorLength>,
     VersionedClause<ACCC_Worker>
   ];
   let allowedExclusiveClauses = [
     VersionedClause<ACCC_Auto>,
     VersionedClause<ACCC_Independent>,
let allowedClauses = [
     VersionedClause<ACCC_Copyout>,
     VersionedClause<ACCC_Create>,
     VersionedClause<ACCC_DevicePtr>,
     VersionedClause<ACCC_DeviceType>,
     VersionedClause<ACCC_FirstPrivate>,
     VersionedClause<ACCC_NoCreate>,
     VersionedClause<ACCC_Present>,
     VersionedClause<ACCC_Private>,
+    VersionedClause<ACCC_Reduction>,
     VersionedClause<ACCC_Wait>
   ];
   let allowedOnceClauses = [
     VersionedClause<ACCC_Async>,
     VersionedClause<ACCC_Collapse>,
     VersionedClause<ACCC_Default>,
     VersionedClause<ACCC_Gang>,
     VersionedClause<ACCC_If>,
-    VersionedClause<ACCC_Reduction>,
     VersionedClause<ACCC_Self>,
     VersionedClause<ACCC_Tile>,
     VersionedClause<ACCC_Vector>,
     VersionedClause<ACCC_Worker>
   ];
   let allowedExclusiveClauses = [
     VersionedClause<ACCC_Auto>,
     VersionedClause<ACCC_Independent>,
     VersionedClause<ACCC_Seq>
   ];
 }
 
 def ACC_Unknown : Directive<"unknown"> {
   let isDefault = true;
 }