[AST][OpenMP] OpenMP Sections / Section constructs contain Structured blocks

[lebedev.ri]

Summary

I'm working on a clang-tidy check, much like existing bugprone-exception-escape,
to detect when an exception might escape out of an OpenMP construct it isn't supposed to escape from.
For that i will be using the nothrow bit of CapturedDecls.

While that bit is already correctly set for some constructs, e.g. #pragma omp parallel: https://godbolt.org/z/2La7pv
it isn't set for the #pragma omp sections, or #pragma omp section: https://godbolt.org/z/qZ-EbP

If i'm reading [[ https://www.openmp.org/wp-content/uploads/OpenMP-API-Specification-5.0.pdf | OpenMP Application Programming Interface Version 5.0 November 2018 ]] correctly,
they should be, as per 2.8.1 sections Construct, starting with page 86:

• The sections construct is a non-iterative worksharing construct that contains a set of structured blocks that are to be distributed among and executed by the threads in a team. Each structured block is executed once by one of the threads in the team in the context of its implicit task.
• The syntax of the sections construct is as follows: #pragma omp sections [clause[ [,] clause] ... ] new-line { [#pragma omp section new-line] structured-block ...
• Description Each structured block in the sections construct is preceded by a section directive except possibly the first block, for which a preceding section directive is optional.

• Restrictions • The code enclosed in a sections construct must be a structured block.
  • A throw executed inside a sections region must cause execution to resume within the same section of the sections region, and the same thread that threw the exception must catch it.

[ABataev]

LG

[lebedev.ri]

In D57585#1380673, @ABataev wrote:

LG

Okay, that sounds promising, thank you for the review!

lib/Sema/SemaOpenMP.cpp

for (Stmt *SectionStmt : llvm::make_range(std::next(S.begin()), S.end())) {
       cast<OMPSectionDirective>(SectionStmt)
           ->setHasCancel(DSAStack->isCancelRegion());
     }
   } else {
     Diag(AStmt->getBeginLoc(), diag::err_omp_sections_not_compound_stmt);
     return StmtError();
   }
 
+  // 1.2.2 OpenMP Language Terminology
+  // Structured block - An executable statement with a single entry at the
+  // top and a single exit at the bottom.
+  // The point of exit cannot be a branch out of the structured block.
+  // longjmp() and throw() must not violate the entry/exit criteria.
+  cast<CapturedStmt>(AStmt)->getCapturedDecl()->setNothrow();
+
   setFunctionHasBranchProtectedScope();
 
   return OMPSectionsDirective::Create(Context, StartLoc, EndLoc, Clauses, AStmt,
                                       DSAStack->isCancelRegion());
 }
 
 StmtResult Sema::ActOnOpenMPSectionDirective(Stmt *AStmt,
                                              SourceLocation StartLoc,
                                              SourceLocation EndLoc) {
   if (!AStmt)
     return StmtError();
 
   assert(isa<CapturedStmt>(AStmt) && "Captured statement expected");
 
+  // 1.2.2 OpenMP Language Terminology
+  // Structured block - An executable statement with a single entry at the
+  // top and a single exit at the bottom.
+  // The point of exit cannot be a branch out of the structured block.
+  // longjmp() and throw() must not violate the entry/exit criteria.
+  cast<CapturedStmt>(AStmt)->getCapturedDecl()->setNothrow();
+
   setFunctionHasBranchProtectedScope();
   DSAStack->setParentCancelRegion(DSAStack->isCancelRegion());
 
   return OMPSectionDirective::Create(Context, StartLoc, EndLoc, AStmt,
                                      DSAStack->isCancelRegion());
 }
 
 StmtResult Sema::ActOnOpenMPSingleDirective(ArrayRef<OMPClause *> Clauses,

test/AST/ast-dump-openmp-sections.cpp

+// RUN: %clang_cc1 -verify -fopenmp -ast-dump %s | FileCheck %s
+// RUN: %clang_cc1 -verify -fopenmp-simd -ast-dump %s | FileCheck %s
+// expected-no-diagnostics
+
+void sections() {
+#pragma omp sections
+  {
+#pragma omp section
+    {
+    }
+#pragma omp section
+    {
+    }
+  }
+}
+
+// CHECK: `-FunctionDecl
+// CHECK-NEXT:   `-CompoundStmt
+// CHECK-NEXT:     `-OMPSectionsDirective
+// CHECK-NEXT:       `-CapturedStmt
+// CHECK-NEXT:         `-CapturedDecl {{.*}} nothrow
+// CHECK-NEXT:           |-CompoundStmt
+// CHECK-NEXT:           | |-OMPSectionDirective
+// CHECK-NEXT:           | | `-CapturedStmt
+// CHECK-NEXT:           | |   `-CapturedDecl {{.*}} nothrow
+// CHECK-NEXT:           | |     |-CompoundStmt
+// CHECK-NEXT:           | |     `-ImplicitParamDecl
+// CHECK-NEXT:           | `-OMPSectionDirective
+// CHECK-NEXT:           |   `-CapturedStmt
+// CHECK-NEXT:           |     `-CapturedDecl {{.*}} nothrow
+// CHECK-NEXT:           |       |-CompoundStmt
+// CHECK-NEXT:           |       `-ImplicitParamDecl
+// CHECK-NEXT:           |-ImplicitParamDecl
+// CHECK-NEXT:           |-CXXRecordDecl
+// CHECK-NEXT:           | |-DefinitionData
+// CHECK-NEXT:           | | |-DefaultConstructor
+// CHECK-NEXT:           | | |-CopyConstructor
+// CHECK-NEXT:           | | |-MoveConstructor
+// CHECK-NEXT:           | | |-CopyAssignment
+// CHECK-NEXT:           | | |-MoveAssignment
+// CHECK-NEXT:           | | `-Destructor
+// CHECK-NEXT:           | `-CapturedRecordAttr
+// CHECK-NEXT:           |-CapturedDecl {{.*}} nothrow
+// CHECK-NEXT:           | |-CompoundStmt
+// CHECK-NEXT:           | `-ImplicitParamDecl
+// CHECK-NEXT:           |-CXXRecordDecl
+// CHECK-NEXT:           | |-DefinitionData
+// CHECK-NEXT:           | | |-DefaultConstructor
+// CHECK-NEXT:           | | |-CopyConstructor
+// CHECK-NEXT:           | | |-MoveConstructor
+// CHECK-NEXT:           | | |-CopyAssignment
+// CHECK-NEXT:           | | |-MoveAssignment
+// CHECK-NEXT:           | | `-Destructor
+// CHECK-NEXT:           | `-CapturedRecordAttr
+// CHECK-NEXT:           `-CapturedDecl {{.*}} nothrow
+// CHECK-NEXT:             |-CompoundStmt
+// CHECK-NEXT:             `-ImplicitParamDecl