[flang][acc] Allow nested gang loops inside acc routines (#158693)

The following commit incorrectly prohibited nested gang loops inside acc
routines. This PR limits the restriction to loops within kernels
constructs only.
8470027

Author: khaki3

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

@@ -136,10 +136,10 @@ void AccStructureChecker::CheckNotInComputeConstruct() {
   }
 }
 
-bool AccStructureChecker::IsInsideParallelConstruct() const {
+bool AccStructureChecker::IsInsideKernelsConstruct() const {
   if (auto directive = getParentComputeConstruct())
-    if (*directive == llvm::acc::ACCD_parallel ||
-        *directive == llvm::acc::ACCD_parallel_loop)
+    if (*directive == llvm::acc::ACCD_kernels ||
+        *directive == llvm::acc::ACCD_kernels_loop)
       return true;
   return false;
 }
@@ -293,7 +293,10 @@ void AccStructureChecker::CheckNotInSameOrSubLevelLoopConstruct() {
           bool invalid{false};
           if (parentClause == llvm::acc::Clause::ACCC_gang &&
               cl == llvm::acc::Clause::ACCC_gang) {
-            if (IsInsideParallelConstruct()) {
+            if (IsInsideKernelsConstruct()) {
+              context_.Say(GetContext().clauseSource,
+                  "Nested GANG loops are not allowed in the region of a KERNELS construct"_err_en_US);
+            } else {
               auto parentDim = getGangDimensionSize(parent);
               auto currentDim = getGangDimensionSize(GetContext());
               std::int64_t parentDimNum = 1, currentDimNum = 1;
@@ -317,8 +320,6 @@ void AccStructureChecker::CheckNotInSameOrSubLevelLoopConstruct() {
                     parentDimStr);
                 continue;
               }
-            } else {
-              invalid = true;
             }
           } else if (parentClause == llvm::acc::Clause::ACCC_worker &&
               (cl == llvm::acc::Clause::ACCC_gang ||

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

@@ -101,7 +101,7 @@ class AccStructureChecker
   bool IsLoopConstruct(llvm::acc::Directive directive) const;
   std::optional<llvm::acc::Directive> getParentComputeConstruct() const;
   bool IsInsideComputeConstruct() const;
-  bool IsInsideParallelConstruct() const;
+  bool IsInsideKernelsConstruct() const;
   void CheckNotInComputeConstruct();
   std::optional<std::int64_t> getGangDimensionSize(
       DirectiveContext &dirContext);

flang/test/Semantics/OpenACC/acc-loop.f90

@@ -340,10 +340,10 @@ program openacc_loop_validity
 
   !$acc kernels loop gang(dim:3)
   do i = 1, n
-    !ERROR: GANG clause is not allowed in the region of a loop with the GANG clause
+    !ERROR: Nested GANG loops are not allowed in the region of a KERNELS construct
     !$acc loop gang(dim:2)
     do j = 1, n
-      !ERROR: GANG clause is not allowed in the region of a loop with the GANG clause
+      !ERROR: Nested GANG loops are not allowed in the region of a KERNELS construct
       !$acc loop gang(dim:1) worker vector
       do k = 1, i
       end do
@@ -447,4 +447,35 @@ program openacc_loop_validity
     END DO
   END DO
 
+contains
+
+  subroutine sub1()
+    !$acc routine gang(dim:2)
+    implicit none
+    integer, parameter :: N = 256
+    integer :: i, j
+
+    !$acc loop gang(dim:2)
+    DO j = 1, N
+       !$acc loop gang(dim:1) vector
+       DO i = 1, N
+       END DO
+    END DO
+  end subroutine sub1
+
+  subroutine sub2()
+    !$acc routine gang(dim:2)
+    implicit none
+    integer, parameter :: N = 256
+    integer :: i, j
+
+    !$acc loop gang(dim:2)
+    DO j = 1, N
+       !ERROR: GANG(dim:2) clause is not allowed in the region of a loop with the GANG(dim:2) clause
+       !$acc loop gang(dim:2) vector
+       DO i = 1, N
+       END DO
+    END DO
+  end subroutine sub2
+
 end program openacc_loop_validity