[OpenACC] Implement 'gang' clause for Combined Constructs

This one is a bit complicated, as it has some interesting interactions,
as 'gang' Sema is required to look at its containing compute construct.
Except in the case of a combined construct, they are the same. This
resulted in a large refactor of the checking code for CheckGangExpr,
plus some additional work on the diagnostics for its interaction with
'num_gangs' and 'vector'/'worker'.

Author: erichkeane

clang/include/clang/AST/OpenACCClause.h

@@ -483,6 +483,14 @@ class OpenACCGangClause final
     return {getGangKind(I), getExprs()[I]};
   }
 
+  bool hasExprOfKind(OpenACCGangKind GK) const {
+    for (unsigned I = 0; I < getNumExprs(); ++I) {
+      if (getGangKind(I) == GK)
+        return true;
+    }
+    return false;
+  }
+
   static OpenACCGangClause *
   Create(const ASTContext &Ctx, SourceLocation BeginLoc,
          SourceLocation LParenLoc, ArrayRef<OpenACCGangKind> GangKinds,

clang/include/clang/Basic/DiagnosticSemaKinds.td

@@ -12755,21 +12755,22 @@ def err_acc_gang_multiple_elt
     : Error<"OpenACC 'gang' clause may have at most one %select{unnamed or "
             "'num'|'dim'|'static'}0 argument">;
 def err_acc_int_arg_invalid
-    : Error<"'%1' argument on '%0' clause is not permitted on a%select{n "
-            "orphaned|||}2 'loop' construct %select{|associated with a "
-            "'parallel' compute construct|associated with a 'kernels' compute "
-            "construct|associated with a 'serial' compute construct}2">;
+    : Error<"'%0' argument on '%1' clause is not permitted on a%select{|n "
+            "orphaned}2 '%3' construct%select{| associated with a '%5' compute "
+            "construct}4">;
 def err_acc_gang_dim_value
     : Error<"argument to 'gang' clause dimension must be %select{a constant "
             "expression|1, 2, or 3: evaluated to %1}0">;
 def err_acc_num_arg_conflict
-    : Error<"'num' argument to '%0' clause not allowed on a 'loop' construct "
-            "associated with a 'kernels' construct that has a "
-            "'%select{num_gangs|num_workers|vector_length}1' "
-            "clause">;
+    : Error<"'num' argument to '%0' clause not allowed on a '%1' "
+            "construct%select{| associated with a '%3' construct}2 that has a "
+            "'%4' clause">;
+def err_acc_num_arg_conflict_reverse
+    : Error<"'num_gangs' clause not allowed on a 'kernels loop' construct that "
+            "has a 'gang' clause with a 'num' argument">;
 def err_acc_clause_in_clause_region
     : Error<"loop with a '%0' clause may not exist in the region of a '%1' "
-            "clause%select{| on a 'kernels' compute construct}2">;
+            "clause%select{| on a '%3' construct}2">;
 def err_acc_gang_reduction_conflict
     : Error<"%select{OpenACC 'gang' clause with a 'dim' value greater than "
             "1|OpenACC 'reduction' clause}0 cannot "

clang/include/clang/Sema/SemaOpenACC.h

@@ -164,9 +164,14 @@ class SemaOpenACC : public SemaBase {
   }
 
   /// If there is a current 'active' loop construct with a 'gang' clause on a
-  /// 'kernel' construct, this will have the source location for it. This
-  /// permits us to implement the restriction of no further 'gang' clauses.
-  SourceLocation LoopGangClauseOnKernelLoc;
+  /// 'kernel' construct, this will have the source location for it, and the
+  /// 'kernel kind'. This permits us to implement the restriction of no further
+  /// 'gang' clauses.
+  struct LoopGangOnKernelTy {
+    SourceLocation Loc;
+    OpenACCDirectiveKind DirKind = OpenACCDirectiveKind::Invalid;
+  } LoopGangClauseOnKernel;
+
   /// If there is a current 'active' loop construct with a 'worker' clause on it
   /// (on any sort of construct), this has the source location for it.  This
   /// permits us to implement the restriction of no further 'gang' or 'worker'
@@ -705,7 +710,9 @@ class SemaOpenACC : public SemaBase {
   ExprResult CheckTileSizeExpr(Expr *SizeExpr);
 
   // Check a single expression on a gang clause.
-  ExprResult CheckGangExpr(OpenACCGangKind GK, Expr *E);
+  ExprResult CheckGangExpr(ArrayRef<const OpenACCClause *> ExistingClauses,
+                           OpenACCDirectiveKind DK, OpenACCGangKind GK,
+                           Expr *E);
 
   // Does the checking for a 'gang' clause that needs to be done in dependent
   // and not dependent cases.
@@ -771,7 +778,7 @@ class SemaOpenACC : public SemaBase {
     SemaOpenACC &SemaRef;
     ComputeConstructInfo OldActiveComputeConstructInfo;
     OpenACCDirectiveKind DirKind;
-    SourceLocation OldLoopGangClauseOnKernelLoc;
+    LoopGangOnKernelTy OldLoopGangClauseOnKernel;
     SourceLocation OldLoopWorkerClauseLoc;
     SourceLocation OldLoopVectorClauseLoc;
     LoopWithoutSeqCheckingInfo OldLoopWithoutSeqInfo;