improved construct termination and control flow error recovery

12 files changed, 283 insertions, 229 deletions

diff --git a/include/flang/Basic/DiagnosticSemaKinds.td b/include/flang/Basic/DiagnosticSemaKinds.td
index f96aece914..dc3f105672 100644
--- a/include/flang/Basic/DiagnosticSemaKinds.td
+++ b/include/flang/Basic/DiagnosticSemaKinds.td
@@ -112,15 +112,15 @@ def warn_unused_stmt_label : Warning<"unused statement label '%0'">,
   InGroup<UnusedLabel>, DefaultIgnore;
 
 def err_expected_stmt_label_end_do : Error<
-  "expected a statement with a statement label '%0' to mark the end of a do loop">;
+  "expected a do termination statement with a statement label '%0'">;
 
 def err_invalid_do_terminating_stmt : Error<
   "invalid terminating statement for a DO loop">;
 
 def err_stmt_not_in_if : Error<
-  "'%0' statement must be a part of an if construct">;
+  "use of '%0' outside an if construct">;
 def err_end_do_without_do : Error<
-  "use of 'END DO' without the do statement">;
+  "use of 'end do' outside a do construct">;
 
 def err_use_implicit_none_stmt : Error<
   "use of 'IMPLICIT NONE' after 'IMPLICIT'">;
diff --git a/include/flang/Sema/Scope.h b/include/flang/Sema/Scope.h
index 8036cc4e8a..d04f0bfb71 100644
--- a/include/flang/Sema/Scope.h
+++ b/include/flang/Sema/Scope.h
@@ -56,8 +56,9 @@ public:
     Entry(IfStmt *S)
       : Statement(S), BeginOffset(0) {
     }
-    inline bool is(Stmt::StmtClass StmtType) const {
-      return Statement->getStmtClass() == StmtType;
+
+    bool hasExpectedDoLabel() const {
+      return ExpectedEndDoLabel != nullptr;
     }
   };
 
@@ -75,13 +76,12 @@ public:
     return StmtList;
   }
 
-  inline const Entry &LastEntered() const {
+  const Entry &LastEntered() const {
     return ControlFlowStack.back();
   }
-  inline bool HasEntered() const {
+  bool HasEntered() const {
     return ControlFlowStack.size() != 0;
   }
-  bool HasEntered(Stmt::StmtClass StmtType) const;
 
   void Append(Stmt *S);
 private:
@@ -191,7 +191,7 @@ public:
   bool ApplyNone();
 
   /// \brief returns true if IMPLICIT NONE was used in this scope.
-  inline bool isNoneInThisScope() const {
+  bool isNoneInThisScope() const {
     return None;
   }
 
diff --git a/include/flang/Sema/Sema.h b/include/flang/Sema/Sema.h
index f09e8d0cd6..dfe25865ed 100644
--- a/include/flang/Sema/Sema.h
+++ b/include/flang/Sema/Sema.h
@@ -600,6 +600,25 @@ public:
                               SourceLocation Loc,
                               bool ReportUnterminatedLabeledDo = true);
 
+  /// Leaves the last block construct, and performs any clean up
+  /// that might be needed.
+  void LeaveLastBlock();
+
+  /// Leaves block constructs until a do construct is reached.
+  /// NB: the do statements with a termination label such as DO 100 I = ..
+  /// are popped.
+  Stmt *LeaveBlocksUntilDo(SourceLocation Loc);
+
+  /// Returns true if the current statement is inside a do construct which
+  /// is terminated by the given statement label.
+  bool IsInLabeledDo(const Expr *StmtLabel);
+
+  /// Leaves block constructs until a label termination do construct is reached.
+  DoStmt *LeaveBlocksUntilLabeledDo(SourceLocation Loc, const Expr *StmtLabel);
+
+  /// Leaves block constructs until an if construct is reached.
+  IfStmt *LeaveBlocksUntilIf(SourceLocation Loc);
+
 };
 
 } // end flang namespace
diff --git a/lib/Sema/Sema.cpp b/lib/Sema/Sema.cpp
index 1bf7b7bd86..7275cd9793 100644
--- a/lib/Sema/Sema.cpp
+++ b/lib/Sema/Sema.cpp
@@ -76,39 +76,6 @@ void Sema::PushExecutableProgramUnit(ExecutableProgramUnitScope &Scope) {
   CurExecutableStmts = &Scope.Body;
 }
 
-// Unterminated labeled do statement
-static void ReportUnterminatedLabeledDoStmt(DiagnosticsEngine &Diags,
-                                            const BlockStmtBuilder::Entry &S,
-                                            SourceLocation Loc) {
-  std::string Str;
-  llvm::raw_string_ostream Stream(Str);
-  S.ExpectedEndDoLabel->dump(Stream);
-  Diags.Report(Loc, diag::err_expected_stmt_label_end_do) << Stream.str();
-}
-
-// Unterminated if/do statement
-void Sema::ReportUnterminatedStmt(const BlockStmtBuilder::Entry &S,
-                                  SourceLocation Loc,
-                                  bool ReportUnterminatedLabeledDo) {
-  const char * Keyword;
-  switch(S.Statement->getStmtClass()) {
-  case Stmt::IfStmtClass: Keyword = "END IF"; break;
-  case Stmt::DoWhileStmtClass:
-  case Stmt::DoStmtClass: {
-    if(S.ExpectedEndDoLabel) {
-      if(ReportUnterminatedLabeledDo)
-        ReportUnterminatedLabeledDoStmt(Diags, S, Loc);
-      return;
-    }
-    else Keyword = "END DO";
-    break;
-  }
-  default:
-    llvm_unreachable("Invalid stmt");
-  }
-  Diags.Report(Loc, diag::err_expected_kw) << Keyword;
-}
-
 void Sema::PopExecutableProgramUnit(SourceLocation Loc) {
 
   // Fix the forward statement label references
@@ -162,7 +129,7 @@ void BlockStmtBuilder::Enter(Entry S) {
 }
 
 Stmt *BlockStmtBuilder::CreateBody(ASTContext &C,
-                                             const Entry &Last) {
+                                   const Entry &Last) {
   auto Ref = ArrayRef<Stmt*>(StmtList);
   return BlockStmt::Create(C, Last.Statement->getLocation(),
                            ArrayRef<Stmt*>(Ref.begin() + Last.BeginOffset,
@@ -198,13 +165,6 @@ Stmt *BlockStmtBuilder::LeaveOuterBody(ASTContext &C, SourceLocation Loc) {
   return BlockStmt::Create(C, Loc, StmtList);
 }
 
-bool BlockStmtBuilder::HasEntered(Stmt::StmtClass StmtType) const {
-  for(auto I : ControlFlowStack) {
-    if(I.is(StmtType)) return true;
-  }
-  return false;
-}
-
 void BlockStmtBuilder::Append(Stmt *S) {
   assert(S);
   StmtList.push_back(S);
diff --git a/lib/Sema/SemaExecStmt.cpp b/lib/Sema/SemaExecStmt.cpp
index d138d448d0..708dc00097 100644
--- a/lib/Sema/SemaExecStmt.cpp
+++ b/lib/Sema/SemaExecStmt.cpp
@@ -7,8 +7,8 @@
 //
 //===----------------------------------------------------------------------===//
 //
-// This file implements the checking and AST construction for the DATA
-// statement.
+// This file implements the checking and AST construction for the executable
+// statements.
 //
 //===----------------------------------------------------------------------===//
 
@@ -16,6 +16,7 @@
 #include "flang/Sema/DeclSpec.h"
 #include "flang/Sema/SemaDiagnostic.h"
 #include "flang/Sema/SemaInternal.h"
+#include "flang/Parse/ParseDiagnostic.h"
 #include "flang/AST/ASTContext.h"
 #include "flang/AST/Decl.h"
 #include "flang/AST/Stmt.h"
@@ -103,6 +104,10 @@ StmtResult Sema::ActOnGotoStmt(ASTContext &C, SourceLocation Loc,
   return Result;
 }
 
+// =========================================================================
+// Block statements entry
+// =========================================================================
+
 StmtResult Sema::ActOnIfStmt(ASTContext &C, SourceLocation Loc,
                              ExprResult Condition, Expr *StmtLabel) {
   if(Condition.isUsable())
@@ -116,98 +121,6 @@ StmtResult Sema::ActOnIfStmt(ASTContext &C, SourceLocation Loc,
   return Result;
 }
 
-StmtResult Sema::ActOnElseIfStmt(ASTContext &C, SourceLocation Loc,
-                                 ExprResult Condition, Expr *StmtLabel) {
-  if(!getCurrentBody()->HasEntered() ||
-     !getCurrentBody()->LastEntered().is(Stmt::IfStmtClass)) {
-    if(getCurrentBody()->HasEntered(Stmt::IfStmtClass))
-      ReportUnterminatedStmt( getCurrentBody()->LastEntered(), Loc);
-    else
-      Diags.Report(Loc, diag::err_stmt_not_in_if) << "ELSE IF";
-    return StmtError();
-  }
-
-  // typecheck
-  if(Condition.isUsable())
-    StmtRequiresLogicalExpression(Loc, Condition.get());
-
-  auto Result = IfStmt::Create(C, Loc, Condition.get(), StmtLabel);
-  auto ParentIf = cast<IfStmt>(getCurrentBody()->LastEntered().Statement);
-  getCurrentBody()->Leave(C);
-  if(Condition.isUsable())
-    ParentIf->setElseStmt(Result);
-  if(StmtLabel) DeclareStatementLabel(StmtLabel, Result);
-  getCurrentBody()->Enter(Result);
-  return Result;
-}
-
-StmtResult Sema::ActOnElseStmt(ASTContext &C, SourceLocation Loc, Expr *StmtLabel) {
-  if(!getCurrentBody()->HasEntered() ||
-     !getCurrentBody()->LastEntered().is(Stmt::IfStmtClass)) {
-    if(getCurrentBody()->HasEntered(Stmt::IfStmtClass))
-      ReportUnterminatedStmt(getCurrentBody()->LastEntered(), Loc);
-    else
-      Diags.Report(Loc, diag::err_stmt_not_in_if) << "ELSE";
-    return StmtError();
-  }
-  auto Result = ConstructPartStmt::Create(C, ConstructPartStmt::ElseStmtClass, Loc, nullptr, StmtLabel);
-  getCurrentBody()->Append(Result);
-  getCurrentBody()->LeaveIfThen(C);
-  if(StmtLabel) DeclareStatementLabel(StmtLabel, Result);
-  return Result;
-}
-
-StmtResult Sema::ActOnEndIfStmt(ASTContext &C, SourceLocation Loc, Expr *StmtLabel) {
-  // Report begin .. end mismatch
-  if(!getCurrentBody()->HasEntered() ||
-     !getCurrentBody()->LastEntered().is(Stmt::IfStmtClass)) {
-    if(getCurrentBody()->HasEntered(Stmt::IfStmtClass))
-      ReportUnterminatedStmt(getCurrentBody()->LastEntered(), Loc);
-    else
-      Diags.Report(Loc, diag::err_stmt_not_in_if) << "END IF";
-    return StmtError();
-  }
-
-  auto Result = ConstructPartStmt::Create(C, ConstructPartStmt::EndIfStmtClass, Loc, nullptr, StmtLabel);
-  getCurrentBody()->Append(Result);
-  getCurrentBody()->Leave(C);
-  if(StmtLabel) DeclareStatementLabel(StmtLabel, Result);
-  return Result;
-}
-
-/// The terminal statement of a DO-loop must not be an unconditional GO TO,
-/// assigned GO TO, arithmetic IF, block IF, ELSE IF, ELSE, END IF, RETURN, STOP, END, or DO statement.
-/// If the terminal statement of a DO-loop is a logical IF statement,
-/// it may contain any executable statement except a DO,
-/// block IF, ELSE IF, ELSE, END IF, END, or another logical IF statement.
-///
-/// FIXME: TODO full
-static bool IsValidDoLogicalIfThenStatement(const Stmt *S) {
-  switch(S->getStmtClass()) {
-  case Stmt::DoStmtClass: case Stmt::IfStmtClass: case Stmt::DoWhileStmtClass:
-  case Stmt::ConstructPartStmtClass:
-    return false;
-  default:
-    return true;
-  }
-}
-
-bool Sema::IsValidDoTerminatingStatement(const Stmt *S) {
-  switch(S->getStmtClass()) {
-  case Stmt::GotoStmtClass: case Stmt::AssignedGotoStmtClass:
-  case Stmt::StopStmtClass: case Stmt::DoStmtClass:
-  case Stmt::DoWhileStmtClass:
-  case Stmt::ConstructPartStmtClass:
-    return false;
-  case Stmt::IfStmtClass: {
-    auto NextStmt = cast<IfStmt>(S)->getThenStmt();
-    return NextStmt && IsValidDoLogicalIfThenStatement(NextStmt);
-  }
-  default:
-    return true;
-  }
-}
-
 void StmtLabelResolver::VisitDoStmt(DoStmt *S) {
   S->setTerminatingStmt(StmtLabelReference(StmtLabelDecl));
 }
@@ -271,44 +184,6 @@ StmtResult Sema::ActOnDoStmt(ASTContext &C, SourceLocation Loc, SourceLocation E
   return Result;
 }
 
-/// FIXME: Fortran 90+: make multiple do end at one label obsolete
-void Sema::CheckStatementLabelEndDo(Expr *StmtLabel, Stmt *S) {
-  if(!getCurrentBody()->HasEntered())
-    return;
-
-  auto I = getCurrentBody()->ControlFlowStack.size();
-  size_t LastUnterminated = 0;
-  do {
-    I--;
-    if(!isa<DoStmt>(getCurrentBody()->ControlFlowStack[I].Statement)) {
-      if(!LastUnterminated) LastUnterminated = I;
-    } else {
-      auto ParentDo = cast<DoStmt>(getCurrentBody()->ControlFlowStack[I].Statement);
-      auto ParentDoExpectedLabel = getCurrentBody()->ControlFlowStack[I].ExpectedEndDoLabel;
-      if(!ParentDoExpectedLabel) {
-        if(!LastUnterminated) LastUnterminated = I;
-      } else {
-        if(getCurrentStmtLabelScope()->IsSame(ParentDoExpectedLabel, StmtLabel)) {
-          // END DO
-          getCurrentStmtLabelScope()->RemoveForwardReference(ParentDo);
-          if(!IsValidDoTerminatingStatement(S)) {
-            Diags.Report(S->getLocation(),
-                         diag::err_invalid_do_terminating_stmt);
-          }
-          ParentDo->setTerminatingStmt(StmtLabelReference(S));
-          if(!LastUnterminated) {
-            RemoveLoopVar(ParentDo->getDoVar());
-            getCurrentBody()->Leave(Context);
-          }
-          else
-            ReportUnterminatedStmt(getCurrentBody()->ControlFlowStack[LastUnterminated],
-                                   S->getLocation());
-        } else if(!LastUnterminated) LastUnterminated = I;
-      }
-    }
-  } while(I>0);
-}
-
 StmtResult Sema::ActOnDoWhileStmt(ASTContext &C, SourceLocation Loc, ExprResult Condition,
                                   Expr *StmtLabel) {
   if(Condition.isUsable())
@@ -321,43 +196,212 @@ StmtResult Sema::ActOnDoWhileStmt(ASTContext &C, SourceLocation Loc, ExprResult
   return Result;
 }
 
-StmtResult Sema::ActOnEndDoStmt(ASTContext &C, SourceLocation Loc, Expr *StmtLabel) {
-  // Report begin .. end mismatch
-  if(!getCurrentBody()->HasEntered() ||
-     (!isa<DoStmt>(getCurrentBody()->LastEntered().Statement) &&
-      !isa<DoWhileStmt>(getCurrentBody()->LastEntered().Statement))) {
-    bool HasMatchingDo = false;
-    for(auto I : getCurrentBody()->ControlFlowStack) {
-      if(isa<DoWhileStmt>(I.Statement) ||
-        (isa<DoStmt>(I.Statement) && !I.ExpectedEndDoLabel)) {
-        HasMatchingDo = true;
-        break;
+
+// =============================================================
+// Block statements termination and control flow
+// =============================================================
+
+void Sema::ReportUnterminatedStmt(const BlockStmtBuilder::Entry &S,
+                                  SourceLocation Loc,
+                                  bool ReportUnterminatedLabeledDo) {
+  const char *Keyword;
+  const char *BeginKeyword;
+  switch(S.Statement->getStmtClass()) {
+  case Stmt::IfStmtClass:
+    Keyword = "end if";
+    BeginKeyword = "if";
+    break;
+  case Stmt::DoWhileStmtClass:
+  case Stmt::DoStmtClass: {
+    if(S.ExpectedEndDoLabel) {
+      if(ReportUnterminatedLabeledDo) {
+        std::string Str;
+        llvm::raw_string_ostream Stream(Str);
+        S.ExpectedEndDoLabel->dump(Stream);
+        Diags.Report(Loc, diag::err_expected_stmt_label_end_do) << Stream.str();
+        Diags.Report(S.Statement->getLocation(), diag::note_matching) << "do";
       }
+      return;
     }
-    if(!HasMatchingDo)
-      Diags.Report(Loc, diag::err_end_do_without_do);
-    else ReportUnterminatedStmt(getCurrentBody()->LastEntered(), Loc);
-    return StmtError();
+    Keyword = "end do";
+    BeginKeyword = "do";
+    break;
+  }
+  default:
+    llvm_unreachable("Invalid stmt");
+  }
+  Diags.Report(Loc, diag::err_expected_kw) << Keyword;
+  Diags.Report(S.Statement->getLocation(), diag::note_matching) << BeginKeyword;
+}
+
+void Sema::LeaveLastBlock() {
+  auto Last = getCurrentBody()->LastEntered().Statement;
+  if(auto Do = dyn_cast<DoStmt>(Last)) {
+    RemoveLoopVar(Do->getDoVar());
   }
+  getCurrentBody()->Leave(Context);
+}
 
-  auto Last = getCurrentBody()->LastEntered();
+IfStmt *Sema::LeaveBlocksUntilIf(SourceLocation Loc) {
+  auto Stack = getCurrentBody()->ControlFlowStack;
+  for(size_t I = Stack.size(); I != 0;) {
+    --I;
+    if(auto If = dyn_cast<IfStmt>(Stack[I].Statement))
+      return If;
+    ReportUnterminatedStmt(Stack[I], Loc);
+    LeaveLastBlock();
+  }
+  return nullptr;
+}
 
-  if(auto Do = dyn_cast<DoStmt>(Last.Statement)) {
-    // If last loop was a DO with terminating label, we expect it to finish before this loop
-    if(getCurrentBody()->LastEntered().ExpectedEndDoLabel) {
-      //FIXME: ReportUnterminatedLabeledDoStmt(getCurrentBody()->LastEntered(), Loc);
-      return StmtError();
+Stmt *Sema::LeaveBlocksUntilDo(SourceLocation Loc) {
+  auto Stack = getCurrentBody()->ControlFlowStack;
+  for(size_t I = Stack.size(); I != 0;) {
+    --I;
+    auto S = Stack[I].Statement;
+    if(isa<DoWhileStmt>(S) ||
+       isa<DoStmt>(S) && !Stack[I].hasExpectedDoLabel())
+      return S;
+    ReportUnterminatedStmt(Stack[I], Loc);
+    LeaveLastBlock();
+  }
+  return nullptr;
+}
+
+/// The terminal statement of a DO-loop must not be an unconditional GO TO,
+/// assigned GO TO, arithmetic IF, block IF, ELSE IF, ELSE, END IF, RETURN, STOP, END, or DO statement.
+/// If the terminal statement of a DO-loop is a logical IF statement,
+/// it may contain any executable statement except a DO,
+/// block IF, ELSE IF, ELSE, END IF, END, or another logical IF statement.
+///
+/// FIXME: TODO full
+static bool IsValidDoLogicalIfThenStatement(const Stmt *S) {
+  switch(S->getStmtClass()) {
+  case Stmt::DoStmtClass: case Stmt::IfStmtClass: case Stmt::DoWhileStmtClass:
+  case Stmt::ConstructPartStmtClass:
+    return false;
+  default:
+    return true;
+  }
+}
+
+bool Sema::IsValidDoTerminatingStatement(const Stmt *S) {
+  switch(S->getStmtClass()) {
+  case Stmt::GotoStmtClass: case Stmt::AssignedGotoStmtClass:
+  case Stmt::StopStmtClass: case Stmt::DoStmtClass:
+  case Stmt::DoWhileStmtClass:
+  case Stmt::ConstructPartStmtClass:
+    return false;
+  case Stmt::IfStmtClass: {
+    auto NextStmt = cast<IfStmt>(S)->getThenStmt();
+    return NextStmt && IsValidDoLogicalIfThenStatement(NextStmt);
+  }
+  default:
+    return true;
+  }
+}
+
+bool Sema::IsInLabeledDo(const Expr *StmtLabel) {
+  auto Stack = getCurrentBody()->ControlFlowStack;
+  for(size_t I = Stack.size(); I != 0;) {
+    --I;
+    if(isa<DoStmt>(Stack[I].Statement)) {
+      if(Stack[I].hasExpectedDoLabel()) {
+        if(getCurrentStmtLabelScope()->IsSame(Stack[I].ExpectedEndDoLabel, StmtLabel))
+          return true;
+      }
     }
-    RemoveLoopVar(Do->getDoVar());
   }
+  return false;
+}
+
+DoStmt *Sema::LeaveBlocksUntilLabeledDo(SourceLocation Loc, const Expr *StmtLabel) {
+  auto Stack = getCurrentBody()->ControlFlowStack;
+  for(size_t I = Stack.size(); I != 0;) {
+    --I;
+    if(auto Do = dyn_cast<DoStmt>(Stack[I].Statement)) {
+      if(Stack[I].hasExpectedDoLabel()) {
+        if(getCurrentStmtLabelScope()->IsSame(Stack[I].ExpectedEndDoLabel, StmtLabel))
+          return Do;
+      }
+    }
+    ReportUnterminatedStmt(Stack[I], Loc);
+    LeaveLastBlock();
+  }
+  return nullptr;
+}
+
+StmtResult Sema::ActOnElseIfStmt(ASTContext &C, SourceLocation Loc,
+                                 ExprResult Condition, Expr *StmtLabel) {
+  auto IfBegin = LeaveBlocksUntilIf(Loc);
+  if(!IfBegin)
+    Diags.Report(Loc, diag::err_stmt_not_in_if) << "else if";
+
+  // typecheck
+  if(Condition.isUsable())
+    StmtRequiresLogicalExpression(Loc, Condition.get());
+
+  auto Result = IfStmt::Create(C, Loc, Condition.get(), StmtLabel);
+  if(IfBegin) {
+    LeaveLastBlock();
+    if(Condition.isUsable())
+      IfBegin->setElseStmt(Result);
+  }
+  if(StmtLabel) DeclareStatementLabel(StmtLabel, Result);
+  getCurrentBody()->Enter(Result);
+  return Result;
+}
+
+StmtResult Sema::ActOnElseStmt(ASTContext &C, SourceLocation Loc, Expr *StmtLabel) {
+  auto IfBegin = LeaveBlocksUntilIf(Loc);
+  if(!IfBegin)
+    Diags.Report(Loc, diag::err_stmt_not_in_if) << "else";
+
+  auto Result = ConstructPartStmt::Create(C, ConstructPartStmt::ElseStmtClass, Loc, nullptr, StmtLabel);
+  getCurrentBody()->Append(Result);
+  if(IfBegin) getCurrentBody()->LeaveIfThen(C);
+  if(StmtLabel) DeclareStatementLabel(StmtLabel, Result);
+  return Result;
+}
+
+StmtResult Sema::ActOnEndIfStmt(ASTContext &C, SourceLocation Loc, Expr *StmtLabel) {
+  auto IfBegin = LeaveBlocksUntilIf(Loc);
+  if(!IfBegin)
+    Diags.Report(Loc, diag::err_stmt_not_in_if) << "end if";
+
+  auto Result = ConstructPartStmt::Create(C, ConstructPartStmt::EndIfStmtClass, Loc, nullptr, StmtLabel);
+  getCurrentBody()->Append(Result);
+  if(IfBegin) LeaveLastBlock();
+  if(StmtLabel) DeclareStatementLabel(StmtLabel, Result);
+  return Result;
+}
+
+StmtResult Sema::ActOnEndDoStmt(ASTContext &C, SourceLocation Loc, Expr *StmtLabel) {
+  auto DoBegin = LeaveBlocksUntilDo(Loc);
+  if(!DoBegin)
+    Diags.Report(Loc, diag::err_end_do_without_do);
 
   auto Result = ConstructPartStmt::Create(C, ConstructPartStmt::EndDoStmtClass, Loc, nullptr, StmtLabel);
   getCurrentBody()->Append(Result);
-  getCurrentBody()->Leave(C);
+  if(DoBegin) LeaveLastBlock();
   if(StmtLabel) DeclareStatementLabel(StmtLabel, Result);
   return Result;
 }
 
+/// FIXME: Fortran 90+: make multiple do end at one label obsolete
+void Sema::CheckStatementLabelEndDo(Expr *StmtLabel, Stmt *S) {
+  if(!getCurrentBody()->HasEntered()) return;
+  if(!IsInLabeledDo(StmtLabel)) return;
+  auto DoBegin = LeaveBlocksUntilLabeledDo(S->getLocation(), StmtLabel);
+
+  getCurrentStmtLabelScope()->RemoveForwardReference(DoBegin);
+  if(!IsValidDoTerminatingStatement(S))
+    Diags.Report(S->getLocation(), diag::err_invalid_do_terminating_stmt);
+  DoBegin->setTerminatingStmt(StmtLabelReference(S));
+  LeaveLastBlock();
+}
+
+
 StmtResult Sema::ActOnContinueStmt(ASTContext &C, SourceLocation Loc, Expr *StmtLabel) {
   auto Result = ContinueStmt::Create(C, Loc, StmtLabel);
   getCurrentBody()->Append(Result);
diff --git a/test/Parser/do.f95 b/test/Parser/do.f95
index 2f3d69a94a..d732f491a7 100644
--- a/test/Parser/do.f95
+++ b/test/Parser/do.f95
@@ -50,7 +50,6 @@ PROGRAM dotest
     ENDDO
 
     DO x I = 1,2 ! expected-error {{expected '='}}
-    ! END DO
+    END DO
 
-    DO I = 1,5 ! expected-error@+1 {{expected 'END DO'}}
 END PROGRAM
diff --git a/test/Parser/if.f95 b/test/Parser/if.f95
index 2c3397bc13..7657c53155 100644
--- a/test/Parser/if.f95
+++ b/test/Parser/if.f95
@@ -56,6 +56,6 @@ PROGRAM iftest
     ENDIF
   END IF
 
-  IF(1 == 2) THEN
-    C = "NO" ! expected-error@+1 {{expected 'END IF'}}
+  IF(1 == 2) THEN ! expected-note {{to match this 'if'}}
+    C = "NO" ! expected-error@+1 {{expected 'end if'}}
 END PROGRAM iftest
diff --git a/test/Sema/beginEndRecovery.f95 b/test/Sema/beginEndRecovery.f95
new file mode 100644
index 0000000000..4defe9b5db
--- /dev/null
+++ b/test/Sema/beginEndRecovery.f95
@@ -0,0 +1,36 @@
+! RUN: %flang -fsyntax-only -verify < %s
+
+program recovery
+
+  do i = 1, 10
+    if (i == 0) then ! expected-note {{to match this 'if'}}
+  end do ! expected-error {{expected 'end if'}}
+
+  do while(.true.) ! expected-error@+3 {{expected a do termination statement with a statement label '100'}}
+    do 100 i = 1, 10   ! expected-note {{to match this 'do'}}
+      if (i == 0) then ! expected-note {{to match this 'if'}}
+  end do ! expected-error {{expected 'end if'}}
+
+  i = 0
+
+  if(i == 1) then
+    do i = 1, 10 ! expected-note {{to match this 'do'}}
+  end if ! expected-error {{expected 'end do'}}
+
+  if(i == 1) then
+    do i = 1, 10 ! expected-note {{to match this 'do'}}
+  else ! expected-error {{expected 'end do'}}
+  end if
+
+  if(i == 1) then
+    do 100 i = 1,10 ! expected-note {{to match this 'do'}}
+  else if(i == 3) then ! expected-error {{expected a do termination statement with a statement label '100'}}
+  end if
+
+  do 200 i = 1,10
+    do j = 1,10  ! expected-note {{to match this 'do'}}
+300   print *,i
+200 continue ! expected-error {{expected 'end do'}}
+
+100 continue
+end
diff --git a/test/Sema/do.f95 b/test/Sema/do.f95
index ebe5f50341..ac6accbdbf 100644
--- a/test/Sema/do.f95
+++ b/test/Sema/do.f95
@@ -12,20 +12,19 @@ PROGRAM dotest
       R = I * R
 10  CONTINUE ! expected-note {{previous definition is here}}
 
-    END DO ! expected-error {{use of 'END DO' without the do statement}}
+    END DO ! expected-error {{use of 'end do' outside a do construct}}
 
     DO 10 I = 1, 5 ! expected-error {{the statement label '10' must be declared after the 'DO' statement}}
 20    R = R * R
 
     DO 25 II = 1, 10
-      IF(.true.) THEN
-25      CONTINUE ! expected-error {{expected 'END IF'}}
-      END IF
+      IF(.true.) THEN ! expected-note {{to match this 'if'}}
+25      CONTINUE ! expected-error {{expected 'end if'}}
 
     DO 666 I = 1, 10,2  ! expected-error {{use of undeclared statement label '666'}}
-      R = I * R
-
-    END DO ! expected-error {{expected a statement with a statement label '666' to mark the end of a do loop}}
+      R = I * R ! expected-note@-1 {{to match this 'do'}}
+    END DO ! expected-error {{expected a do termination statement with a statement label '666'}}
+    CONTINUE ! expected-error@-1 {{use of 'end do' outside a do construct}}
 
     DO 30 C = 1, 3 ! expected-error {{statement requires an integer variable ('complex' invalid)}}
 30  CONTINUE
diff --git a/test/Sema/dowhile.f95 b/test/Sema/dowhile.f95
index 938a3c2fee..6583c6de3b 100644
--- a/test/Sema/dowhile.f95
+++ b/test/Sema/dowhile.f95
@@ -8,8 +8,8 @@ PROGRAM dowhiletest
   END DO
 
   IF(.true.) THEN
-    DO WHILE(.false.)
+    DO WHILE(.false.) ! expected-note {{to match this 'do'}}
 
-    END IF ! expected-error {{expected 'END DO'}}
+    END IF ! expected-error {{expected 'end do'}}
 
-END ! expected-error {{expected 'END DO'}}
+END
diff --git a/test/Sema/if.f95 b/test/Sema/if.f95
index e5b8e40b5a..679711c6bc 100644
--- a/test/Sema/if.f95
+++ b/test/Sema/if.f95
@@ -10,9 +10,9 @@ PROGRAM iftest
     I = 2
   END IF
 
-  ELSE ! expected-error {{'ELSE' statement must be a part of an if construct}}
-  ELSE IF(2 == 2) THEN ! expected-error {{'ELSE IF' statement must be a part of an if construct}}
-  END IF ! expected-error {{'END IF' statement must be a part of an if construct}}
+  ELSE ! expected-error {{use of 'else' outside an if construct}}
+  ELSE IF(2 == 2) THEN ! expected-error {{use of 'else if' outside an if construct}}
+  END IF ! FIXME: report as out of place end if?
 
   IF(2) THEN ! expected-error {{statement requires an expression of logical type ('integer' invalid)}}
     I = 3
@@ -28,8 +28,4 @@ PROGRAM iftest
     I = 3
   END IF
 
-  IF(.true.) THEN
-    DO I = 1, 10
-  END IF ! expected-error {{expected 'END DO'}}
-
-END PROGRAM ! expected-error {{expected 'END DO'}}
+END PROGRAM
diff --git a/test/Sema/subprogram.f95 b/test/Sema/subprogram.f95
index fd21665569..88d51a68ab 100644
--- a/test/Sema/subprogram.f95
+++ b/test/Sema/subprogram.f95
@@ -22,8 +22,9 @@ END
 SUBROUTINE SUBB ! expected-note {{previous definition is here}}
   INTEGER SUBB ! expected-error {{redefinition of 'subb'}}
   REAL FUNC2
-  IF(SUBB .EQ. 0) FUNC2 = 0 ! expected-error {{expected a variable}}
-END ! expected-error {{expected 'END IF'}}
+  LOGICAL L
+  L = SUBB .EQ. 0 ! expected-error {{expected a variable}}
+END
 
 FUNCTION FUNC3()
   INTEGER FUNC3