[flang][OpenMP] Add functionality to check "close nesting" of regions, which can be used for Semantic checks.

[arnamoy10]

Summary

This patch adds a function to help Semantic checks that deal with "closely nesting" condition check.

Also modifies the closely nesting semantic check code for worksharing regions. Previously the check was checking only the immediate parent. e.g

!$omp do
 !omp target
  !$omp do

In the previous code, though the inside do is closely nested inside the outside do (no parallel in between), the existing check would not catch the violation, as the immediate parent of the nested do is target.

With the new function, this condition will be caught.

More test cases are added to check more scenarios.

[kiranchandramohan]

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

130

I was thinking you will be doing the following. Is there an issue with this approach?

1. curIndex = index of top of stack
2. curDir = Directive at curIndex
3. If (curDir is a violating nesting) return true
4. if (curDir is parallel) return false
5. if curIndex == -1 return false
6. curIndex = curIndex - 1
7. goto step 2

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

169

Can you change the name to IsCloselyNestedRegion.

Note that the definition of closely nested construct is different. A construct nested inside another construct with no other construct nested between them.

[arnamoy10]

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

130

I do not think I understand Step 3: If (curDir is a violating nesting) return true

Let's say we are doing the violation check that barrier is not allowed inside a task

$!omp task
  $!omp target
    $!omp barrier --> top of stack

So curDir is barrier. Could you tell me how step 3 would work as per your algorithm?

[kiranchandramohan]

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

130

In the algorithm I was suggesting the assumption I made is that the top of stack is !$omp target and not !$omp barrier.

[arnamoy10]

1. Updating the algorithm as per suggestion
2. Modified the name of the function to IsCloselyNestedRegion()

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

130

That makes sense, thank you. I think the suggested algorithm is cleaner and I updated the patch with the implementation

[kiranchandramohan]

LGTM. Thanks for the changes and the tests.

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

#include "llvm/Frontend/OpenMP/OMP.inc"
   llvm::omp::Clause GetClauseKindForParserClass(const A &) {
 #define GEN_FLANG_CLAUSE_PARSER_KIND_MAP
 #include "llvm/Frontend/OpenMP/OMP.inc"
   }
 
 private:
   bool HasInvalidWorksharingNesting(
       const parser::CharBlock &, const OmpDirectiveSet &);
-
+  bool IsCloselyNestedRegion(const OmpDirectiveSet &set);
   // specific clause related
   bool ScheduleModifierHasType(const parser::OmpScheduleClause &,
       const parser::OmpScheduleModifierType::ModType &);
   void CheckAllowedMapTypes(const parser::OmpMapType::Type &,
       const std::list<parser::OmpMapType::Type> &);
   llvm::StringRef getClauseName(llvm::omp::Clause clause) override;
   llvm::StringRef getDirectiveName(llvm::omp::Directive directive) override;
 

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

 
 private:
   SemanticsContext &context_;
   const parser::CharBlock *cycleSource_;
   std::int64_t cycleLevel_;
   std::map<std::string, std::int64_t> labelNamesandLevels_;
 };
 
+bool OmpStructureChecker::IsCloselyNestedRegion(const OmpDirectiveSet &set) {
+  // Definition of close nesting:
+  //
+  // `A region nested inside another region with no parallel region nested
+  // between them`
+  //
+  // Examples:
+  //   non-parallel construct 1
+  //    non-parallel construct 2
+  //      parallel construct
+  //        construct 3
+  // In the above example, construct 3 is NOT closely nested inside construct 1
+  // or 2
+  //
+  //   non-parallel construct 1
+  //    non-parallel construct 2
+  //        construct 3
+  // In the above example, construct 3 is closely nested inside BOTH construct 1
+  // and 2
+  //
+  // Algorithm:
+  // Starting from the parent context, Check in a bottom-up fashion, each level
+  // of the context stack. If we have a match for one of the (supplied)
+  // violating directives, `close nesting` is satisfied. If no match is there in
+  // the entire stack, `close nesting` is not satisfied. If at any level, a
+  // `parallel` region is found, `close nesting` is not satisfied.
+
+  if (CurrentDirectiveIsNested()) {
+    int index = dirContext_.size() - 2;
+    while (index != -1) {
+      if (set.test(dirContext_[index].directive)) {
+        return true;
+      } else if (llvm::omp::parallelSet.test(dirContext_[index].directive)) {
+        return false;
+      }
+      index--;
+    }
+  }
+  return false;
+}
+
 bool OmpStructureChecker::HasInvalidWorksharingNesting(
     const parser::CharBlock &source, const OmpDirectiveSet &set) {
   // set contains all the invalid closely nested directives
   // for the given directive (`source` here)
-  if (CurrentDirectiveIsNested() && set.test(GetContextParent().directive)) {
+  if (IsCloselyNestedRegion(set)) {
     context_.Say(source,
         "A worksharing region may not be closely nested inside a "
         "worksharing, explicit task, taskloop, critical, ordered, atomic, or "
         "master region"_err_en_US);
     return true;
   }
   return false;
 }

flang/test/Semantics/omp-do05.f90

 ! RUN: %S/test_errors.sh %s %t %flang -fopenmp
 ! OpenMP Version 4.5
 ! 2.7.1 Loop Construct restrictions on single directive.
 
 
 program omp_do
 
   integer n
-  integer i,j
+  integer i,j,k
   !$omp do
   do i=1,10
     !ERROR: A worksharing region may not be closely nested inside a worksharing, explicit task, taskloop, critical, ordered, atomic, or master region
     !$omp single
     do j=1,10
       print *,"hello"
     end do
     !$omp end single
   end do
   !$omp end do
 
+  !$omp do
+  do i=1,10
+    !$omp task
+    do j=1,10
+      !ERROR: A worksharing region may not be closely nested inside a worksharing, explicit task, taskloop, critical, ordered, atomic, or master region
+      !$omp single
+      do k=1,10
+        print *,"hello"
+      end do
+      !$omp end single
+    end do
+    !$omp end task
+  end do
+  !$omp end do
+
+  !$omp do
+  do i=1,10
+    !$omp parallel
+    do j=1,10
+      !$omp single
+      do k=1,10
+        print *,"hello"
+      end do
+      !$omp end single
+    end do
+    !$omp end parallel
+  end do
+  !$omp end do
+
+!$omp do
+do i=1,10
+  !ERROR: A worksharing region may not be closely nested inside a worksharing, explicit task, taskloop, critical, ordered, atomic, or master region
+  !$omp single
+  do j=1,10
+    !ERROR: A worksharing region may not be closely nested inside a worksharing, explicit task, taskloop, critical, ordered, atomic, or master region
+    !$omp single
+    do k=1,10
+      print *,"hello"
+    end do
+    !$omp end single
+  end do
+  !$omp end single
+
+  !ERROR: A worksharing region may not be closely nested inside a worksharing, explicit task, taskloop, critical, ordered, atomic, or master region
+  !$omp single
+    do k=1,10
+      print *,"hello"
+    end do
+  !$omp end single
+
+  !ERROR: A worksharing region may not be closely nested inside a worksharing, explicit task, taskloop, critical, ordered, atomic, or master region
+  !$omp do
+    do k=1,10
+      print *,"hello"
+    end do
+  !$omp end do
+end do
+!$omp end do
+
+  !$omp parallel default(shared)
+  !$omp do
+  do i = 1, n
+    !ERROR: A worksharing region may not be closely nested inside a worksharing, explicit task, taskloop, critical, ordered, atomic, or master region
+    !$omp single
+    call work(i, 1)
+    !$omp end single
+  end do
+  !$omp end do
+  !$omp end parallel
+
   !$omp parallel default(shared)
   !$omp do
   do i = 1, n
+    !$omp task
+    do j=1,10
       !ERROR: A worksharing region may not be closely nested inside a worksharing, explicit task, taskloop, critical, ordered, atomic, or master region
       !$omp single
       call work(i, 1)
       !$omp end single
     end do
+    !$omp end task
+  end do
   !$omp end do
   !$omp end parallel
 
 end program omp_do

flang/test/Semantics/omp-nested01.f90

 ! RUN: %S/test_errors.sh %s %t %flang -fopenmp
 
 ! Check OpenMP 2.17 Nesting of Regions
 
   N = 1024
   !$omp do
   do i = 1, N
      !ERROR: A worksharing region may not be closely nested inside a worksharing, explicit task, taskloop, critical, ordered, atomic, or master region
      !$omp do
      do j = 1, N
         a = 3.14
      enddo
   enddo
+
+  !$omp do
+  do i = 1, N
+   !$omp target
+   do k = 1,N
+     !ERROR: A worksharing region may not be closely nested inside a worksharing, explicit task, taskloop, critical, ordered, atomic, or master region
+     !$omp do
+     do j = 1, N
+        a = 3.14
+     enddo
+   enddo
+   !$omp end target
+  enddo
+  
+
+  !$omp do
+  do i = 1, N
+   !$omp parallel
+   do k = 1,N
+     !$omp do
+     do j = 1, N
+        a = 3.14
+     enddo
+   enddo
+   !$omp end parallel
+  enddo
 end

flang/test/Semantics/omp-reduction07.f90

!$omp sections private(k)
   !ERROR: REDUCTION variable 'k' is PRIVATE in outer context must be shared in the parallel regions to which any of the worksharing regions arising from the worksharing construct bind.
   !$omp do reduction(+:k) reduction(max:j)
   do i = 1, 10
     k = k + 1
   end do
   !$omp end do
 !$omp end sections
 
+!$omp sections private(k)
+  !$omp target
+  do j = 1,10
+    !ERROR: A worksharing region may not be closely nested inside a worksharing, explicit task, taskloop, critical, ordered, atomic, or master region
+    !$omp do reduction(+:k) reduction(max:j)
+    do i = 1, 10
+      k = k + 1
+    end do
+    !$omp end do
+  end do
+  !$omp end target
+!$omp end sections
+
 !$omp parallel reduction(+:a)
 !ERROR: REDUCTION variable 'a' is REDUCTION in outer context must be shared in the parallel regions to which any of the worksharing regions arising from the worksharing construct bind.
 !$omp sections reduction(-:a)
 a = 10
 !$omp end sections
 !$omp end parallel
 
 !$omp parallel reduction(-:a)