[AST][OpenMP] OpenMP single Construct contains Structured block

[lebedev.ri]

Summary

[[ https://www.openmp.org/wp-content/uploads/OpenMP-API-Specification-5.0.pdf | OpenMP Application Programming Interface Version 5.0 November 2018 ]], 2.8.2 single Construct, starting with page 89:

• The single construct specifies that the associated structured block is executed by only one of the threads in the team (not necessarily the master thread), in the context of its implicit task.
• Restrictions • A throw executed inside a single region must cause execution to resume within the same single region, and the same thread that threw the exception must catch it.

[ABataev]

LG

[lebedev.ri]

Let's instead solve the problem of structured block not having an AST representation.

lib/Sema/SemaOpenMP.cpp

StmtResult Sema::ActOnOpenMPSingleDirective(ArrayRef<OMPClause *> Clauses,
                                             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();
 
   // OpenMP [2.7.3, single Construct, Restrictions]
   // The copyprivate clause must not be used with the nowait clause.
   const OMPClause *Nowait = nullptr;
   const OMPClause *Copyprivate = nullptr;
   for (const OMPClause *Clause : Clauses) {
     if (Clause->getClauseKind() == OMPC_nowait)

test/AST/ast-dump-openmp-single.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 single() {
+#pragma omp single
+  {
+  }
+}
+
+// CHECK:`-FunctionDecl
+// CHECK-NEXT:  `-CompoundStmt
+// CHECK-NEXT:    `-OMPSingleDirective
+// CHECK-NEXT:      `-CapturedStmt
+// CHECK-NEXT:        `-CapturedDecl {{.*}} nothrow
+// CHECK-NEXT:          |-CompoundStmt
+// CHECK-NEXT:          `-ImplicitParamDecl