diff --git a/clang/include/clang/Basic/DiagnosticSemaKinds.td b/clang/include/clang/Basic/DiagnosticSemaKinds.td
index 0d301e76c92d7..1854c8e522b82 100644
--- a/clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -10523,10 +10523,16 @@ def err_omp_atomic_compare : Error<
   " '{x = x == e ? d : x;}', '{x = e == x ? d : x;}', or 'if(expr ordop x) {x = expr;}', 'if(x ordop expr) {x = expr;}', 'if(x == e) {x = d;}',"
   " 'if(e == x) {x = d;}' where 'x' is an lvalue expression with scalar type, 'expr', 'e', and 'd' are expressions with scalar type,"
   " and 'ordop' is one of '<' or '>'.">;
+def err_omp_atomic_compare_capture : Error<
+  "the statement for 'atomic compare capture' must be a compound statement of form '{v = x; cond-up-stmt}', ''{cond-up-stmt v = x;}', '{if(x == e) {x = d;} else {v = x;}}',"
+  " '{r = x == e; if(r) {x = d;}}', or '{r = x == e; if(r) {x = d;} else {v = x;}}', where 'cond-update-stmt' can have one of the following forms: 'if(expr ordop x) {x = expr;}',"
+  " 'if(x ordop expr) {x = expr;}', 'if(x == e) {x = d;}', or 'if(e == x) {x = d;}' where 'x', 'r', and 'v' are lvalue expressions with scalar type, 'expr', 'e', and 'd' are expressions with scalar type,"
+  " and 'ordop' is one of '<' or '>'.">;
 def note_omp_atomic_compare: Note<
   "%select{expected compound statement|expected exactly one expression statement|expected assignment statement|expected conditional operator|expect result value to be at false expression|"
   "expect binary operator in conditional expression|expect '<', '>' or '==' as order operator|expect comparison in a form of 'x == e', 'e == x', 'x ordop expr', or 'expr ordop x'|"
-  "expect lvalue for result value|expect scalar value|expect integer value|unexpected 'else' statement}0">;
+  "expect lvalue for result value|expect scalar value|expect integer value|unexpected 'else' statement|expect '==' operator|expect an assignment statement 'v = x'|"
+  "expect a 'if' statement|expect no more than two statements|expect a compound statement|expect 'else' statement|expect a form 'r = x == e; if (r) ...'}0">;
 def err_omp_atomic_several_clauses : Error<
   "directive '#pragma omp atomic' cannot contain more than one 'read', 'write', 'update', 'capture', or 'compare' clause">;
 def err_omp_several_mem_order_clauses : Error<
diff --git a/clang/lib/Sema/SemaOpenMP.cpp b/clang/lib/Sema/SemaOpenMP.cpp
index c32609e4e32e3..43386c1ef8edb 100644
--- a/clang/lib/Sema/SemaOpenMP.cpp
+++ b/clang/lib/Sema/SemaOpenMP.cpp
@@ -10976,6 +10976,20 @@ class OpenMPAtomicCompareChecker {
     NotInteger,
     /// 'else' statement is not expected.
     UnexpectedElse,
+    /// Not an equality operator.
+    NotEQ,
+    /// Invalid assignment (not v == x).
+    InvalidAssignment,
+    /// Not if statement
+    NotIfStmt,
+    /// More than two statements in a compund statement.
+    MoreThanTwoStmts,
+    /// Not a compound statement.
+    NotCompoundStmt,
+    /// No else statement.
+    NoElse,
+    /// Not 'if (r)'.
+    InvalidCondition,
     /// No error.
     NoError,
   };
@@ -10999,7 +11013,7 @@ class OpenMPAtomicCompareChecker {
   Expr *getCond() const { return C; }
   bool isXBinopExpr() const { return IsXBinopExpr; }
 
-private:
+protected:
   /// Reference to ASTContext
   ASTContext &ContextRef;
   /// 'x' lvalue part of the source atomic expression.
@@ -11026,6 +11040,35 @@ class OpenMPAtomicCompareChecker {
 
   /// Check if all captured values have right type.
   bool checkType(ErrorInfoTy &ErrorInfo) const;
+
+  static bool CheckValue(const Expr *E, ErrorInfoTy &ErrorInfo,
+                         bool ShouldBeLValue) {
+    if (ShouldBeLValue && !E->isLValue()) {
+      ErrorInfo.Error = ErrorTy::XNotLValue;
+      ErrorInfo.ErrorLoc = ErrorInfo.NoteLoc = E->getExprLoc();
+      ErrorInfo.ErrorRange = ErrorInfo.NoteRange = E->getSourceRange();
+      return false;
+    }
+
+    if (!E->isInstantiationDependent()) {
+      QualType QTy = E->getType();
+      if (!QTy->isScalarType()) {
+        ErrorInfo.Error = ErrorTy::NotScalar;
+        ErrorInfo.ErrorLoc = ErrorInfo.NoteLoc = E->getExprLoc();
+        ErrorInfo.ErrorRange = ErrorInfo.NoteRange = E->getSourceRange();
+        return false;
+      }
+
+      if (!QTy->isIntegerType()) {
+        ErrorInfo.Error = ErrorTy::NotInteger;
+        ErrorInfo.ErrorLoc = ErrorInfo.NoteLoc = E->getExprLoc();
+        ErrorInfo.ErrorRange = ErrorInfo.NoteRange = E->getSourceRange();
+        return false;
+      }
+    }
+
+    return true;
+  }
 };
 
 bool OpenMPAtomicCompareChecker::checkCondUpdateStmt(IfStmt *S,
@@ -11215,41 +11258,13 @@ bool OpenMPAtomicCompareChecker::checkType(ErrorInfoTy &ErrorInfo) const {
   // 'x' and 'e' cannot be nullptr
   assert(X && E && "X and E cannot be nullptr");
 
-  auto CheckValue = [&ErrorInfo](const Expr *E, bool ShouldBeLValue) {
-    if (ShouldBeLValue && !E->isLValue()) {
-      ErrorInfo.Error = ErrorTy::XNotLValue;
-      ErrorInfo.ErrorLoc = ErrorInfo.NoteLoc = E->getExprLoc();
-      ErrorInfo.ErrorRange = ErrorInfo.NoteRange = E->getSourceRange();
-      return false;
-    }
-
-    if (!E->isInstantiationDependent()) {
-      QualType QTy = E->getType();
-      if (!QTy->isScalarType()) {
-        ErrorInfo.Error = ErrorTy::NotScalar;
-        ErrorInfo.ErrorLoc = ErrorInfo.NoteLoc = E->getExprLoc();
-        ErrorInfo.ErrorRange = ErrorInfo.NoteRange = E->getSourceRange();
-        return false;
-      }
-
-      if (!QTy->isIntegerType()) {
-        ErrorInfo.Error = ErrorTy::NotInteger;
-        ErrorInfo.ErrorLoc = ErrorInfo.NoteLoc = E->getExprLoc();
-        ErrorInfo.ErrorRange = ErrorInfo.NoteRange = E->getSourceRange();
-        return false;
-      }
-    }
-
-    return true;
-  };
-
-  if (!CheckValue(X, true))
+  if (!CheckValue(X, ErrorInfo, true))
     return false;
 
-  if (!CheckValue(E, false))
+  if (!CheckValue(E, ErrorInfo, false))
     return false;
 
-  if (D && !CheckValue(D, false))
+  if (D && !CheckValue(D, ErrorInfo, false))
     return false;
 
   return true;
@@ -11297,6 +11312,413 @@ bool OpenMPAtomicCompareChecker::checkStmt(
 
   return checkType(ErrorInfo);
 }
+
+class OpenMPAtomicCompareCaptureChecker final
+    : public OpenMPAtomicCompareChecker {
+public:
+  OpenMPAtomicCompareCaptureChecker(Sema &S) : OpenMPAtomicCompareChecker(S) {}
+
+  Expr *getV() const { return V; }
+  Expr *getR() const { return R; }
+  bool isFailOnly() const { return IsFailOnly; }
+
+  /// Check if statement \a S is valid for <tt>atomic compare capture</tt>.
+  bool checkStmt(Stmt *S, ErrorInfoTy &ErrorInfo);
+
+private:
+  bool checkType(ErrorInfoTy &ErrorInfo);
+
+  // NOTE: Form 3, 4, 5 in the following comments mean the 3rd, 4th, and 5th
+  // form of 'conditional-update-capture-atomic' structured block on the v5.2
+  // spec p.p. 82:
+  // (1) { v = x; cond-update-stmt }
+  // (2) { cond-update-stmt v = x; }
+  // (3) if(x == e) { x = d; } else { v = x; }
+  // (4) { r = x == e; if(r) { x = d; } }
+  // (5) { r = x == e; if(r) { x = d; } else { v = x; } }
+
+  /// Check if it is valid 'if(x == e) { x = d; } else { v = x; }' (form 3)
+  bool checkForm3(IfStmt *S, ErrorInfoTy &ErrorInfo);
+
+  /// Check if it is valid '{ r = x == e; if(r) { x = d; } }',
+  /// or '{ r = x == e; if(r) { x = d; } else { v = x; } }' (form 4 and 5)
+  bool checkForm45(Stmt *S, ErrorInfoTy &ErrorInfo);
+
+  /// 'v' lvalue part of the source atomic expression.
+  Expr *V = nullptr;
+  /// 'r' lvalue part of the source atomic expression.
+  Expr *R = nullptr;
+  /// If 'v' is only updated when the comparison fails.
+  bool IsFailOnly = false;
+};
+
+bool OpenMPAtomicCompareCaptureChecker::checkType(ErrorInfoTy &ErrorInfo) {
+  if (!OpenMPAtomicCompareChecker::checkType(ErrorInfo))
+    return false;
+
+  if (V && !CheckValue(V, ErrorInfo, true))
+    return false;
+
+  if (R && !CheckValue(R, ErrorInfo, true))
+    return false;
+
+  return true;
+}
+
+bool OpenMPAtomicCompareCaptureChecker::checkForm3(IfStmt *S,
+                                                   ErrorInfoTy &ErrorInfo) {
+  IsFailOnly = true;
+
+  auto *Then = S->getThen();
+  if (auto *CS = dyn_cast<CompoundStmt>(Then)) {
+    if (CS->body_empty()) {
+      ErrorInfo.Error = ErrorTy::NoStmt;
+      ErrorInfo.ErrorLoc = ErrorInfo.NoteLoc = CS->getBeginLoc();
+      ErrorInfo.ErrorRange = ErrorInfo.NoteRange = CS->getSourceRange();
+      return false;
+    }
+    if (CS->size() > 1) {
+      ErrorInfo.Error = ErrorTy::MoreThanOneStmt;
+      ErrorInfo.ErrorLoc = ErrorInfo.NoteLoc = CS->getBeginLoc();
+      ErrorInfo.ErrorRange = ErrorInfo.NoteRange = CS->getSourceRange();
+      return false;
+    }
+    Then = CS->body_front();
+  }
+
+  auto *BO = dyn_cast<BinaryOperator>(Then);
+  if (!BO) {
+    ErrorInfo.Error = ErrorTy::NotAnAssignment;
+    ErrorInfo.ErrorLoc = ErrorInfo.NoteLoc = Then->getBeginLoc();
+    ErrorInfo.ErrorRange = ErrorInfo.NoteRange = Then->getSourceRange();
+    return false;
+  }
+  if (BO->getOpcode() != BO_Assign) {
+    ErrorInfo.Error = ErrorTy::NotAnAssignment;
+    ErrorInfo.ErrorLoc = BO->getExprLoc();
+    ErrorInfo.NoteLoc = BO->getOperatorLoc();
+    ErrorInfo.ErrorRange = ErrorInfo.NoteRange = BO->getSourceRange();
+    return false;
+  }
+
+  X = BO->getLHS();
+  D = BO->getRHS();
+
+  auto *Cond = dyn_cast<BinaryOperator>(S->getCond());
+  if (!Cond) {
+    ErrorInfo.Error = ErrorTy::NotABinaryOp;
+    ErrorInfo.ErrorLoc = ErrorInfo.NoteLoc = S->getCond()->getExprLoc();
+    ErrorInfo.ErrorRange = ErrorInfo.NoteRange = S->getCond()->getSourceRange();
+    return false;
+  }
+  if (Cond->getOpcode() != BO_EQ) {
+    ErrorInfo.Error = ErrorTy::NotEQ;
+    ErrorInfo.ErrorLoc = ErrorInfo.NoteLoc = Cond->getExprLoc();
+    ErrorInfo.ErrorRange = ErrorInfo.NoteRange = Cond->getSourceRange();
+    return false;
+  }
+
+  if (checkIfTwoExprsAreSame(ContextRef, X, Cond->getLHS())) {
+    E = Cond->getRHS();
+  } else if (checkIfTwoExprsAreSame(ContextRef, X, Cond->getRHS())) {
+    E = Cond->getLHS();
+  } else {
+    ErrorInfo.Error = ErrorTy::InvalidComparison;
+    ErrorInfo.ErrorLoc = ErrorInfo.NoteLoc = Cond->getExprLoc();
+    ErrorInfo.ErrorRange = ErrorInfo.NoteRange = Cond->getSourceRange();
+    return false;
+  }
+
+  C = Cond;
+
+  if (!S->getElse()) {
+    ErrorInfo.Error = ErrorTy::NoElse;
+    ErrorInfo.ErrorLoc = ErrorInfo.NoteLoc = S->getBeginLoc();
+    ErrorInfo.ErrorRange = ErrorInfo.NoteRange = S->getSourceRange();
+    return false;
+  }
+
+  auto *Else = S->getElse();
+  if (auto *CS = dyn_cast<CompoundStmt>(Else)) {
+    if (CS->body_empty()) {
+      ErrorInfo.Error = ErrorTy::NoStmt;
+      ErrorInfo.ErrorLoc = ErrorInfo.NoteLoc = CS->getBeginLoc();
+      ErrorInfo.ErrorRange = ErrorInfo.NoteRange = CS->getSourceRange();
+      return false;
+    }
+    if (CS->size() > 1) {
+      ErrorInfo.Error = ErrorTy::MoreThanOneStmt;
+      ErrorInfo.ErrorLoc = ErrorInfo.NoteLoc = CS->getBeginLoc();
+      ErrorInfo.ErrorRange = ErrorInfo.NoteRange = S->getSourceRange();
+      return false;
+    }
+    Else = CS->body_front();
+  }
+
+  auto *ElseBO = dyn_cast<BinaryOperator>(Else);
+  if (!ElseBO) {
+    ErrorInfo.Error = ErrorTy::NotAnAssignment;
+    ErrorInfo.ErrorLoc = ErrorInfo.NoteLoc = Else->getBeginLoc();
+    ErrorInfo.ErrorRange = ErrorInfo.NoteRange = Else->getSourceRange();
+    return false;
+  }
+  if (ElseBO->getOpcode() != BO_Assign) {
+    ErrorInfo.Error = ErrorTy::NotAnAssignment;
+    ErrorInfo.ErrorLoc = ElseBO->getExprLoc();
+    ErrorInfo.NoteLoc = ElseBO->getOperatorLoc();
+    ErrorInfo.ErrorRange = ErrorInfo.NoteRange = ElseBO->getSourceRange();
+    return false;
+  }
+
+  if (!checkIfTwoExprsAreSame(ContextRef, X, ElseBO->getRHS())) {
+    ErrorInfo.Error = ErrorTy::InvalidAssignment;
+    ErrorInfo.ErrorLoc = ErrorInfo.NoteLoc = ElseBO->getRHS()->getExprLoc();
+    ErrorInfo.ErrorRange = ErrorInfo.NoteRange =
+        ElseBO->getRHS()->getSourceRange();
+    return false;
+  }
+
+  V = ElseBO->getLHS();
+
+  return checkType(ErrorInfo);
+}
+
+bool OpenMPAtomicCompareCaptureChecker::checkForm45(Stmt *S,
+                                                    ErrorInfoTy &ErrorInfo) {
+  // We don't check here as they should be already done before call this
+  // function.
+  auto *CS = cast<CompoundStmt>(S);
+  assert(CS->size() == 2 && "CompoundStmt size is not expected");
+  auto *S1 = cast<BinaryOperator>(CS->body_front());
+  auto *S2 = cast<IfStmt>(CS->body_back());
+  assert(S1->getOpcode() == BO_Assign && "unexpected binary operator");
+
+  if (!checkIfTwoExprsAreSame(ContextRef, S1->getLHS(), S2->getCond())) {
+    ErrorInfo.Error = ErrorTy::InvalidCondition;
+    ErrorInfo.ErrorLoc = ErrorInfo.NoteLoc = S2->getCond()->getExprLoc();
+    ErrorInfo.ErrorRange = ErrorInfo.NoteRange = S1->getLHS()->getSourceRange();
+    return false;
+  }
+
+  R = S1->getLHS();
+
+  auto *Then = S2->getThen();
+  if (auto *ThenCS = dyn_cast<CompoundStmt>(Then)) {
+    if (ThenCS->body_empty()) {
+      ErrorInfo.Error = ErrorTy::NoStmt;
+      ErrorInfo.ErrorLoc = ErrorInfo.NoteLoc = ThenCS->getBeginLoc();
+      ErrorInfo.ErrorRange = ErrorInfo.NoteRange = ThenCS->getSourceRange();
+      return false;
+    }
+    if (ThenCS->size() > 1) {
+      ErrorInfo.Error = ErrorTy::MoreThanOneStmt;
+      ErrorInfo.ErrorLoc = ErrorInfo.NoteLoc = ThenCS->getBeginLoc();
+      ErrorInfo.ErrorRange = ErrorInfo.NoteRange = ThenCS->getSourceRange();
+      return false;
+    }
+    Then = ThenCS->body_front();
+  }
+
+  auto *ThenBO = dyn_cast<BinaryOperator>(Then);
+  if (!ThenBO) {
+    ErrorInfo.Error = ErrorTy::NotAnAssignment;
+    ErrorInfo.ErrorLoc = ErrorInfo.NoteLoc = S2->getBeginLoc();
+    ErrorInfo.ErrorRange = ErrorInfo.NoteRange = S2->getSourceRange();
+    return false;
+  }
+  if (ThenBO->getOpcode() != BO_Assign) {
+    ErrorInfo.Error = ErrorTy::NotAnAssignment;
+    ErrorInfo.ErrorLoc = ThenBO->getExprLoc();
+    ErrorInfo.NoteLoc = ThenBO->getOperatorLoc();
+    ErrorInfo.ErrorRange = ErrorInfo.NoteRange = ThenBO->getSourceRange();
+    return false;
+  }
+
+  X = ThenBO->getLHS();
+  D = ThenBO->getRHS();
+
+  auto *BO = cast<BinaryOperator>(S1->getRHS()->IgnoreImpCasts());
+  if (BO->getOpcode() != BO_EQ) {
+    ErrorInfo.Error = ErrorTy::NotEQ;
+    ErrorInfo.ErrorLoc = BO->getExprLoc();
+    ErrorInfo.NoteLoc = BO->getOperatorLoc();
+    ErrorInfo.ErrorRange = ErrorInfo.NoteRange = BO->getSourceRange();
+    return false;
+  }
+
+  C = BO;
+
+  if (checkIfTwoExprsAreSame(ContextRef, X, BO->getLHS())) {
+    E = BO->getRHS();
+  } else if (checkIfTwoExprsAreSame(ContextRef, X, BO->getRHS())) {
+    E = BO->getLHS();
+  } else {
+    ErrorInfo.Error = ErrorTy::InvalidComparison;
+    ErrorInfo.ErrorLoc = ErrorInfo.NoteLoc = BO->getExprLoc();
+    ErrorInfo.ErrorRange = ErrorInfo.NoteRange = BO->getSourceRange();
+    return false;
+  }
+
+  if (S2->getElse()) {
+    IsFailOnly = true;
+
+    auto *Else = S2->getElse();
+    if (auto *ElseCS = dyn_cast<CompoundStmt>(Else)) {
+      if (ElseCS->body_empty()) {
+        ErrorInfo.Error = ErrorTy::NoStmt;
+        ErrorInfo.ErrorLoc = ErrorInfo.NoteLoc = ElseCS->getBeginLoc();
+        ErrorInfo.ErrorRange = ErrorInfo.NoteRange = ElseCS->getSourceRange();
+        return false;
+      }
+      if (ElseCS->size() > 1) {
+        ErrorInfo.Error = ErrorTy::MoreThanOneStmt;
+        ErrorInfo.ErrorLoc = ErrorInfo.NoteLoc = ElseCS->getBeginLoc();
+        ErrorInfo.ErrorRange = ErrorInfo.NoteRange = ElseCS->getSourceRange();
+        return false;
+      }
+      Else = ElseCS->body_front();
+    }
+
+    auto *ElseBO = dyn_cast<BinaryOperator>(Else);
+    if (!ElseBO) {
+      ErrorInfo.Error = ErrorTy::NotAnAssignment;
+      ErrorInfo.ErrorLoc = ErrorInfo.NoteLoc = Else->getBeginLoc();
+      ErrorInfo.ErrorRange = ErrorInfo.NoteRange = Else->getSourceRange();
+      return false;
+    }
+    if (ElseBO->getOpcode() != BO_Assign) {
+      ErrorInfo.Error = ErrorTy::NotAnAssignment;
+      ErrorInfo.ErrorLoc = ElseBO->getExprLoc();
+      ErrorInfo.NoteLoc = ElseBO->getOperatorLoc();
+      ErrorInfo.ErrorRange = ErrorInfo.NoteRange = ElseBO->getSourceRange();
+      return false;
+    }
+    if (!checkIfTwoExprsAreSame(ContextRef, X, ElseBO->getRHS())) {
+      ErrorInfo.Error = ErrorTy::InvalidAssignment;
+      ErrorInfo.ErrorLoc = ElseBO->getRHS()->getExprLoc();
+      ErrorInfo.NoteLoc = X->getExprLoc();
+      ErrorInfo.ErrorRange = ElseBO->getRHS()->getSourceRange();
+      ErrorInfo.NoteRange = X->getSourceRange();
+      return false;
+    }
+
+    V = ElseBO->getLHS();
+  }
+
+  return checkType(ErrorInfo);
+}
+
+bool OpenMPAtomicCompareCaptureChecker::checkStmt(Stmt *S,
+                                                  ErrorInfoTy &ErrorInfo) {
+  // if(x == e) { x = d; } else { v = x; }
+  if (auto *IS = dyn_cast<IfStmt>(S))
+    return checkForm3(IS, ErrorInfo);
+
+  auto *CS = dyn_cast<CompoundStmt>(S);
+  if (!CS) {
+    ErrorInfo.Error = ErrorTy::NotCompoundStmt;
+    ErrorInfo.ErrorLoc = ErrorInfo.NoteLoc = S->getBeginLoc();
+    ErrorInfo.ErrorRange = ErrorInfo.NoteRange = S->getSourceRange();
+    return false;
+  }
+  if (CS->body_empty()) {
+    ErrorInfo.Error = ErrorTy::NoStmt;
+    ErrorInfo.ErrorLoc = ErrorInfo.NoteLoc = CS->getBeginLoc();
+    ErrorInfo.ErrorRange = ErrorInfo.NoteRange = CS->getSourceRange();
+    return false;
+  }
+
+  // { if(x == e) { x = d; } else { v = x; } }
+  if (CS->size() == 1) {
+    auto *IS = dyn_cast<IfStmt>(CS->body_front());
+    if (!IS) {
+      ErrorInfo.Error = ErrorTy::NotIfStmt;
+      ErrorInfo.ErrorLoc = ErrorInfo.NoteLoc = CS->body_front()->getBeginLoc();
+      ErrorInfo.ErrorRange = ErrorInfo.NoteRange =
+          CS->body_front()->getSourceRange();
+      return false;
+    }
+
+    return checkForm3(IS, ErrorInfo);
+  } else if (CS->size() == 2) {
+    auto *S1 = CS->body_front();
+    auto *S2 = CS->body_back();
+
+    Stmt *UpdateStmt = nullptr;
+    Stmt *CondUpdateStmt = nullptr;
+
+    if (auto *BO = dyn_cast<BinaryOperator>(S1)) {
+      // { v = x; cond-update-stmt } or form 45.
+      UpdateStmt = S1;
+      CondUpdateStmt = S2;
+      // Check if form 45.
+      if (dyn_cast<BinaryOperator>(BO->getRHS()->IgnoreImpCasts()) &&
+          dyn_cast<IfStmt>(S2))
+        return checkForm45(CS, ErrorInfo);
+    } else {
+      // { cond-update-stmt v = x; }
+      UpdateStmt = S2;
+      CondUpdateStmt = S1;
+    }
+
+    auto CheckCondUpdateStmt = [this, &ErrorInfo](Stmt *CUS) {
+      auto *IS = dyn_cast<IfStmt>(CUS);
+      if (!IS) {
+        ErrorInfo.Error = ErrorTy::NotIfStmt;
+        ErrorInfo.ErrorLoc = ErrorInfo.NoteLoc = CUS->getBeginLoc();
+        ErrorInfo.ErrorRange = ErrorInfo.NoteRange = CUS->getSourceRange();
+        return false;
+      }
+
+      if (!checkCondUpdateStmt(IS, ErrorInfo))
+        return false;
+
+      return true;
+    };
+
+    // CheckUpdateStmt has to be called *after* CheckCondUpdateStmt.
+    auto CheckUpdateStmt = [this, &ErrorInfo](Stmt *US) {
+      auto *BO = dyn_cast<BinaryOperator>(US);
+      if (!BO) {
+        ErrorInfo.Error = ErrorTy::NotAnAssignment;
+        ErrorInfo.ErrorLoc = ErrorInfo.NoteLoc = US->getBeginLoc();
+        ErrorInfo.ErrorRange = ErrorInfo.NoteRange = US->getSourceRange();
+        return false;
+      }
+      if (BO->getOpcode() != BO_Assign) {
+        ErrorInfo.Error = ErrorTy::NotAnAssignment;
+        ErrorInfo.ErrorLoc = BO->getExprLoc();
+        ErrorInfo.NoteLoc = BO->getOperatorLoc();
+        ErrorInfo.ErrorRange = ErrorInfo.NoteRange = BO->getSourceRange();
+        return false;
+      }
+      if (!checkIfTwoExprsAreSame(ContextRef, this->X, BO->getRHS())) {
+        ErrorInfo.Error = ErrorTy::InvalidAssignment;
+        ErrorInfo.ErrorLoc = BO->getRHS()->getExprLoc();
+        ErrorInfo.NoteLoc = this->X->getExprLoc();
+        ErrorInfo.ErrorRange = BO->getRHS()->getSourceRange();
+        ErrorInfo.NoteRange = this->X->getSourceRange();
+        return false;
+      }
+
+      this->V = BO->getLHS();
+
+      return true;
+    };
+
+    if (!CheckCondUpdateStmt(CondUpdateStmt))
+      return false;
+    if (!CheckUpdateStmt(UpdateStmt))
+      return false;
+  } else {
+    ErrorInfo.Error = ErrorTy::MoreThanTwoStmts;
+    ErrorInfo.ErrorLoc = ErrorInfo.NoteLoc = CS->getBeginLoc();
+    ErrorInfo.ErrorRange = ErrorInfo.NoteRange = CS->getSourceRange();
+    return false;
+  }
+
+  return checkType(ErrorInfo);
+}
 } // namespace
 
 StmtResult Sema::ActOnOpenMPAtomicDirective(ArrayRef<OMPClause *> Clauses,
@@ -11794,6 +12216,15 @@ StmtResult Sema::ActOnOpenMPAtomicDirective(ArrayRef<OMPClause *> Clauses,
       UE = V = E = X = nullptr;
   } else if (AtomicKind == OMPC_compare) {
     if (IsCompareCapture) {
+      OpenMPAtomicCompareCaptureChecker::ErrorInfoTy ErrorInfo;
+      OpenMPAtomicCompareCaptureChecker Checker(*this);
+      if (!Checker.checkStmt(Body, ErrorInfo)) {
+        Diag(ErrorInfo.ErrorLoc, diag::err_omp_atomic_compare_capture)
+            << ErrorInfo.ErrorRange;
+        Diag(ErrorInfo.NoteLoc, diag::note_omp_atomic_compare)
+            << ErrorInfo.Error << ErrorInfo.NoteRange;
+        return StmtError();
+      }
       // TODO: We don't set X, D, E, etc. here because in code gen we will emit
       // error directly.
     } else {
diff --git a/clang/test/OpenMP/atomic_messages.c b/clang/test/OpenMP/atomic_messages.c
index c66cd19b5aca3..4066d7518c628 100644
--- a/clang/test/OpenMP/atomic_messages.c
+++ b/clang/test/OpenMP/atomic_messages.c
@@ -500,4 +500,199 @@ void compare(void) {
       fx = fe;
   }
 }
+
+void compare_capture(void) {
+  int x = 0;
+  int d = 0;
+  int e = 0;
+  int v = 0;
+  int r = 0;
+// omp51-error@+3 {{the statement for 'atomic compare capture' must be a compound statement of form '{v = x; cond-up-stmt}', ''{cond-up-stmt v = x;}', '{if(x == e) {x = d;} else {v = x;}}', '{r = x == e; if(r) {x = d;}}', or '{r = x == e; if(r) {x = d;} else {v = x;}}', where 'cond-update-stmt' can have one of the following forms: 'if(expr ordop x) {x = expr;}', 'if(x ordop expr) {x = expr;}', 'if(x == e) {x = d;}', or 'if(e == x) {x = d;}' where 'x' is an lvalue expression with scalar type, 'expr', 'e', and 'd' are expressions with scalar type, and 'ordop' is one of '<' or '>'.}}
+// omp51-note@+2 {{expected compound statement}}
+#pragma omp atomic compare capture
+  if (x == e) {}
+// omp51-error@+3 {{the statement for 'atomic compare capture' must be a compound statement of form '{v = x; cond-up-stmt}', ''{cond-up-stmt v = x;}', '{if(x == e) {x = d;} else {v = x;}}', '{r = x == e; if(r) {x = d;}}', or '{r = x == e; if(r) {x = d;} else {v = x;}}', where 'cond-update-stmt' can have one of the following forms: 'if(expr ordop x) {x = expr;}', 'if(x ordop expr) {x = expr;}', 'if(x == e) {x = d;}', or 'if(e == x) {x = d;}' where 'x' is an lvalue expression with scalar type, 'expr', 'e', and 'd' are expressions with scalar type, and 'ordop' is one of '<' or '>'.}}
+// omp51-note@+2 {{expected exactly one expression statement}}
+#pragma omp atomic compare capture
+  if (x == e) {
+    x = d;
+    v = x;
+  }
+// omp51-error@+4 {{the statement for 'atomic compare capture' must be a compound statement of form '{v = x; cond-up-stmt}', ''{cond-up-stmt v = x;}', '{if(x == e) {x = d;} else {v = x;}}', '{r = x == e; if(r) {x = d;}}', or '{r = x == e; if(r) {x = d;} else {v = x;}}', where 'cond-update-stmt' can have one of the following forms: 'if(expr ordop x) {x = expr;}', 'if(x ordop expr) {x = expr;}', 'if(x == e) {x = d;}', or 'if(e == x) {x = d;}' where 'x' is an lvalue expression with scalar type, 'expr', 'e', and 'd' are expressions with scalar type, and 'ordop' is one of '<' or '>'.}}
+// omp51-note@+3 {{expected assignment statement}}
+#pragma omp atomic compare capture
+  if (x == e) {
+    bbar();
+  }
+// omp51-error@+4 {{the statement for 'atomic compare capture' must be a compound statement of form '{v = x; cond-up-stmt}', ''{cond-up-stmt v = x;}', '{if(x == e) {x = d;} else {v = x;}}', '{r = x == e; if(r) {x = d;}}', or '{r = x == e; if(r) {x = d;} else {v = x;}}', where 'cond-update-stmt' can have one of the following forms: 'if(expr ordop x) {x = expr;}', 'if(x ordop expr) {x = expr;}', 'if(x == e) {x = d;}', or 'if(e == x) {x = d;}' where 'x' is an lvalue expression with scalar type, 'expr', 'e', and 'd' are expressions with scalar type, and 'ordop' is one of '<' or '>'.}}
+// omp51-note@+3 {{expected assignment statement}}
+#pragma omp atomic compare capture
+  if (x == e) {
+    x += d;
+  }
+// omp51-error@+3 {{the statement for 'atomic compare capture' must be a compound statement of form '{v = x; cond-up-stmt}', ''{cond-up-stmt v = x;}', '{if(x == e) {x = d;} else {v = x;}}', '{r = x == e; if(r) {x = d;}}', or '{r = x == e; if(r) {x = d;} else {v = x;}}', where 'cond-update-stmt' can have one of the following forms: 'if(expr ordop x) {x = expr;}', 'if(x ordop expr) {x = expr;}', 'if(x == e) {x = d;}', or 'if(e == x) {x = d;}' where 'x' is an lvalue expression with scalar type, 'expr', 'e', and 'd' are expressions with scalar type, and 'ordop' is one of '<' or '>'.}}
+// omp51-note@+2 {{expect binary operator in conditional expression}}
+#pragma omp atomic compare capture
+  if (ffoo()) {
+    x = d;
+  }
+// omp51-error@+3 {{the statement for 'atomic compare capture' must be a compound statement of form '{v = x; cond-up-stmt}', ''{cond-up-stmt v = x;}', '{if(x == e) {x = d;} else {v = x;}}', '{r = x == e; if(r) {x = d;}}', or '{r = x == e; if(r) {x = d;} else {v = x;}}', where 'cond-update-stmt' can have one of the following forms: 'if(expr ordop x) {x = expr;}', 'if(x ordop expr) {x = expr;}', 'if(x == e) {x = d;}', or 'if(e == x) {x = d;}' where 'x' is an lvalue expression with scalar type, 'expr', 'e', and 'd' are expressions with scalar type, and 'ordop' is one of '<' or '>'.}}
+// omp51-note@+2 {{expect '==' operator}}
+#pragma omp atomic compare capture
+  if (x > e) {
+    x = d;
+  }
+// omp51-error@+3 {{the statement for 'atomic compare capture' must be a compound statement of form '{v = x; cond-up-stmt}', ''{cond-up-stmt v = x;}', '{if(x == e) {x = d;} else {v = x;}}', '{r = x == e; if(r) {x = d;}}', or '{r = x == e; if(r) {x = d;} else {v = x;}}', where 'cond-update-stmt' can have one of the following forms: 'if(expr ordop x) {x = expr;}', 'if(x ordop expr) {x = expr;}', 'if(x == e) {x = d;}', or 'if(e == x) {x = d;}' where 'x' is an lvalue expression with scalar type, 'expr', 'e', and 'd' are expressions with scalar type, and 'ordop' is one of '<' or '>'.}}
+// omp51-note@+2 {{expect comparison in a form of 'x == e', 'e == x', 'x ordop expr', or 'expr ordop x'}}
+#pragma omp atomic compare capture
+  if (d == e) {
+    x = d;
+  }
+// omp51-error@+3 {{the statement for 'atomic compare capture' must be a compound statement of form '{v = x; cond-up-stmt}', ''{cond-up-stmt v = x;}', '{if(x == e) {x = d;} else {v = x;}}', '{r = x == e; if(r) {x = d;}}', or '{r = x == e; if(r) {x = d;} else {v = x;}}', where 'cond-update-stmt' can have one of the following forms: 'if(expr ordop x) {x = expr;}', 'if(x ordop expr) {x = expr;}', 'if(x == e) {x = d;}', or 'if(e == x) {x = d;}' where 'x' is an lvalue expression with scalar type, 'expr', 'e', and 'd' are expressions with scalar type, and 'ordop' is one of '<' or '>'.}}
+// omp51-note@+2 {{expect 'else' statement}}
+#pragma omp atomic compare capture
+  if (x == e) {
+    x = d;
+  }
+// omp51-error@+5 {{the statement for 'atomic compare capture' must be a compound statement of form '{v = x; cond-up-stmt}', ''{cond-up-stmt v = x;}', '{if(x == e) {x = d;} else {v = x;}}', '{r = x == e; if(r) {x = d;}}', or '{r = x == e; if(r) {x = d;} else {v = x;}}', where 'cond-update-stmt' can have one of the following forms: 'if(expr ordop x) {x = expr;}', 'if(x ordop expr) {x = expr;}', 'if(x == e) {x = d;}', or 'if(e == x) {x = d;}' where 'x' is an lvalue expression with scalar type, 'expr', 'e', and 'd' are expressions with scalar type, and 'ordop' is one of '<' or '>'.}}
+// omp51-note@+4 {{expected compound statement}}
+#pragma omp atomic compare capture
+  if (x == e) {
+    x = d;
+  } else {
+  }
+// omp51-error@+5 {{the statement for 'atomic compare capture' must be a compound statement of form '{v = x; cond-up-stmt}', ''{cond-up-stmt v = x;}', '{if(x == e) {x = d;} else {v = x;}}', '{r = x == e; if(r) {x = d;}}', or '{r = x == e; if(r) {x = d;} else {v = x;}}', where 'cond-update-stmt' can have one of the following forms: 'if(expr ordop x) {x = expr;}', 'if(x ordop expr) {x = expr;}', 'if(x == e) {x = d;}', or 'if(e == x) {x = d;}' where 'x' is an lvalue expression with scalar type, 'expr', 'e', and 'd' are expressions with scalar type, and 'ordop' is one of '<' or '>'.}}
+// omp51-note@+4 {{expected exactly one expression statement}}
+#pragma omp atomic compare capture
+  if (x == e) {
+    x = d;
+  } else {
+    v = x;
+    d = e;
+  }
+// omp51-error@+6 {{the statement for 'atomic compare capture' must be a compound statement of form '{v = x; cond-up-stmt}', ''{cond-up-stmt v = x;}', '{if(x == e) {x = d;} else {v = x;}}', '{r = x == e; if(r) {x = d;}}', or '{r = x == e; if(r) {x = d;} else {v = x;}}', where 'cond-update-stmt' can have one of the following forms: 'if(expr ordop x) {x = expr;}', 'if(x ordop expr) {x = expr;}', 'if(x == e) {x = d;}', or 'if(e == x) {x = d;}' where 'x' is an lvalue expression with scalar type, 'expr', 'e', and 'd' are expressions with scalar type, and 'ordop' is one of '<' or '>'.}}
+// omp51-note@+5 {{expected assignment statement}}
+#pragma omp atomic compare capture
+  if (x == e) {
+    x = d;
+  } else {
+    bbar();
+  }
+// omp51-error@+6 {{the statement for 'atomic compare capture' must be a compound statement of form '{v = x; cond-up-stmt}', ''{cond-up-stmt v = x;}', '{if(x == e) {x = d;} else {v = x;}}', '{r = x == e; if(r) {x = d;}}', or '{r = x == e; if(r) {x = d;} else {v = x;}}', where 'cond-update-stmt' can have one of the following forms: 'if(expr ordop x) {x = expr;}', 'if(x ordop expr) {x = expr;}', 'if(x == e) {x = d;}', or 'if(e == x) {x = d;}' where 'x' is an lvalue expression with scalar type, 'expr', 'e', and 'd' are expressions with scalar type, and 'ordop' is one of '<' or '>'.}}
+// omp51-note@+5 {{expected assignment statement}}
+#pragma omp atomic compare capture
+  if (x == e) {
+    x = d;
+  } else {
+    v += x;
+  }
+// omp51-error@+6 {{the statement for 'atomic compare capture' must be a compound statement of form '{v = x; cond-up-stmt}', ''{cond-up-stmt v = x;}', '{if(x == e) {x = d;} else {v = x;}}', '{r = x == e; if(r) {x = d;}}', or '{r = x == e; if(r) {x = d;} else {v = x;}}', where 'cond-update-stmt' can have one of the following forms: 'if(expr ordop x) {x = expr;}', 'if(x ordop expr) {x = expr;}', 'if(x == e) {x = d;}', or 'if(e == x) {x = d;}' where 'x' is an lvalue expression with scalar type, 'expr', 'e', and 'd' are expressions with scalar type, and 'ordop' is one of '<' or '>'.}}
+// omp51-note@+5 {{expect an assignment statement 'v = x'}}
+#pragma omp atomic compare capture
+  if (x == e) {
+    x = d;
+  } else {
+    v = d;
+  }
+// omp51-error@+3 {{the statement for 'atomic compare capture' must be a compound statement of form '{v = x; cond-up-stmt}', ''{cond-up-stmt v = x;}', '{if(x == e) {x = d;} else {v = x;}}', '{r = x == e; if(r) {x = d;}}', or '{r = x == e; if(r) {x = d;} else {v = x;}}', where 'cond-update-stmt' can have one of the following forms: 'if(expr ordop x) {x = expr;}', 'if(x ordop expr) {x = expr;}', 'if(x == e) {x = d;}', or 'if(e == x) {x = d;}' where 'x' is an lvalue expression with scalar type, 'expr', 'e', and 'd' are expressions with scalar type, and 'ordop' is one of '<' or '>'.}}
+// omp51-note@+2 {{expected compound statement}}
+#pragma omp atomic compare capture
+  {}
+// omp51-error@+3 {{the statement for 'atomic compare capture' must be a compound statement of form '{v = x; cond-up-stmt}', ''{cond-up-stmt v = x;}', '{if(x == e) {x = d;} else {v = x;}}', '{r = x == e; if(r) {x = d;}}', or '{r = x == e; if(r) {x = d;} else {v = x;}}', where 'cond-update-stmt' can have one of the following forms: 'if(expr ordop x) {x = expr;}', 'if(x ordop expr) {x = expr;}', 'if(x == e) {x = d;}', or 'if(e == x) {x = d;}' where 'x' is an lvalue expression with scalar type, 'expr', 'e', and 'd' are expressions with scalar type, and 'ordop' is one of '<' or '>'.}}
+// omp51-note@+2 {{expect a compound statement}}
+#pragma omp atomic compare capture
+  x = x > e ? e : x;
+// omp51-error@+3 {{the statement for 'atomic compare capture' must be a compound statement of form '{v = x; cond-up-stmt}', ''{cond-up-stmt v = x;}', '{if(x == e) {x = d;} else {v = x;}}', '{r = x == e; if(r) {x = d;}}', or '{r = x == e; if(r) {x = d;} else {v = x;}}', where 'cond-update-stmt' can have one of the following forms: 'if(expr ordop x) {x = expr;}', 'if(x ordop expr) {x = expr;}', 'if(x == e) {x = d;}', or 'if(e == x) {x = d;}' where 'x' is an lvalue expression with scalar type, 'expr', 'e', and 'd' are expressions with scalar type, and 'ordop' is one of '<' or '>'.}}
+// omp51-note@+2 {{expect a 'if' statement}}
+#pragma omp atomic compare capture
+  { x = x > e ? e : x; }
+// omp51-error@+3 {{the statement for 'atomic compare capture' must be a compound statement of form '{v = x; cond-up-stmt}', ''{cond-up-stmt v = x;}', '{if(x == e) {x = d;} else {v = x;}}', '{r = x == e; if(r) {x = d;}}', or '{r = x == e; if(r) {x = d;} else {v = x;}}', where 'cond-update-stmt' can have one of the following forms: 'if(expr ordop x) {x = expr;}', 'if(x ordop expr) {x = expr;}', 'if(x == e) {x = d;}', or 'if(e == x) {x = d;}' where 'x' is an lvalue expression with scalar type, 'expr', 'e', and 'd' are expressions with scalar type, and 'ordop' is one of '<' or '>'.}}
+// omp51-note@+2 {{expect a form 'r = x == e; if (r) ...'}}
+#pragma omp atomic compare capture
+  { r = x == e; if (x == d) { x = e; } }
+// omp51-error@+3 {{the statement for 'atomic compare capture' must be a compound statement of form '{v = x; cond-up-stmt}', ''{cond-up-stmt v = x;}', '{if(x == e) {x = d;} else {v = x;}}', '{r = x == e; if(r) {x = d;}}', or '{r = x == e; if(r) {x = d;} else {v = x;}}', where 'cond-update-stmt' can have one of the following forms: 'if(expr ordop x) {x = expr;}', 'if(x ordop expr) {x = expr;}', 'if(x == e) {x = d;}', or 'if(e == x) {x = d;}' where 'x' is an lvalue expression with scalar type, 'expr', 'e', and 'd' are expressions with scalar type, and 'ordop' is one of '<' or '>'.}}
+// omp51-note@+2 {{expected assignment statement}}
+#pragma omp atomic compare capture
+  { r = x == e; if (r) { bbar(); } }
+// omp51-error@+3 {{the statement for 'atomic compare capture' must be a compound statement of form '{v = x; cond-up-stmt}', ''{cond-up-stmt v = x;}', '{if(x == e) {x = d;} else {v = x;}}', '{r = x == e; if(r) {x = d;}}', or '{r = x == e; if(r) {x = d;} else {v = x;}}', where 'cond-update-stmt' can have one of the following forms: 'if(expr ordop x) {x = expr;}', 'if(x ordop expr) {x = expr;}', 'if(x == e) {x = d;}', or 'if(e == x) {x = d;}' where 'x' is an lvalue expression with scalar type, 'expr', 'e', and 'd' are expressions with scalar type, and 'ordop' is one of '<' or '>'.}}
+// omp51-note@+2 {{expected assignment statement}}
+#pragma omp atomic compare capture
+  { r = x == e; if (r) { x += d; } }
+// omp51-error@+3 {{the statement for 'atomic compare capture' must be a compound statement of form '{v = x; cond-up-stmt}', ''{cond-up-stmt v = x;}', '{if(x == e) {x = d;} else {v = x;}}', '{r = x == e; if(r) {x = d;}}', or '{r = x == e; if(r) {x = d;} else {v = x;}}', where 'cond-update-stmt' can have one of the following forms: 'if(expr ordop x) {x = expr;}', 'if(x ordop expr) {x = expr;}', 'if(x == e) {x = d;}', or 'if(e == x) {x = d;}' where 'x' is an lvalue expression with scalar type, 'expr', 'e', and 'd' are expressions with scalar type, and 'ordop' is one of '<' or '>'.}}
+// omp51-note@+2 {{expected compound statement}}
+#pragma omp atomic compare capture
+  { r = x == e; if (r) {} }
+// omp51-error@+5 {{the statement for 'atomic compare capture' must be a compound statement of form '{v = x; cond-up-stmt}', ''{cond-up-stmt v = x;}', '{if(x == e) {x = d;} else {v = x;}}', '{r = x == e; if(r) {x = d;}}', or '{r = x == e; if(r) {x = d;} else {v = x;}}', where 'cond-update-stmt' can have one of the following forms: 'if(expr ordop x) {x = expr;}', 'if(x ordop expr) {x = expr;}', 'if(x == e) {x = d;}', or 'if(e == x) {x = d;}' where 'x' is an lvalue expression with scalar type, 'expr', 'e', and 'd' are expressions with scalar type, and 'ordop' is one of '<' or '>'.}}
+// omp51-note@+4 {{expected exactly one expression statement}}
+#pragma omp atomic compare capture
+  {
+    r = x == e;
+    if (r) {
+      x = d;
+      v = x;
+    }
+  }
+// omp51-error@+3 {{the statement for 'atomic compare capture' must be a compound statement of form '{v = x; cond-up-stmt}', ''{cond-up-stmt v = x;}', '{if(x == e) {x = d;} else {v = x;}}', '{r = x == e; if(r) {x = d;}}', or '{r = x == e; if(r) {x = d;} else {v = x;}}', where 'cond-update-stmt' can have one of the following forms: 'if(expr ordop x) {x = expr;}', 'if(x ordop expr) {x = expr;}', 'if(x == e) {x = d;}', or 'if(e == x) {x = d;}' where 'x' is an lvalue expression with scalar type, 'expr', 'e', and 'd' are expressions with scalar type, and 'ordop' is one of '<' or '>'.}}
+// omp51-note@+2 {{expect '==' operator}}
+#pragma omp atomic compare capture
+  { r = x > e; if (r) { x = d; } }
+// omp51-error@+3 {{the statement for 'atomic compare capture' must be a compound statement of form '{v = x; cond-up-stmt}', ''{cond-up-stmt v = x;}', '{if(x == e) {x = d;} else {v = x;}}', '{r = x == e; if(r) {x = d;}}', or '{r = x == e; if(r) {x = d;} else {v = x;}}', where 'cond-update-stmt' can have one of the following forms: 'if(expr ordop x) {x = expr;}', 'if(x ordop expr) {x = expr;}', 'if(x == e) {x = d;}', or 'if(e == x) {x = d;}' where 'x' is an lvalue expression with scalar type, 'expr', 'e', and 'd' are expressions with scalar type, and 'ordop' is one of '<' or '>'.}}
+// omp51-note@+2 {{expect comparison in a form of 'x == e', 'e == x', 'x ordop expr', or 'expr ordop x'}}
+#pragma omp atomic compare capture
+  { r = d == e; if (r) { x = d; } }
+// omp51-error@+3 {{the statement for 'atomic compare capture' must be a compound statement of form '{v = x; cond-up-stmt}', ''{cond-up-stmt v = x;}', '{if(x == e) {x = d;} else {v = x;}}', '{r = x == e; if(r) {x = d;}}', or '{r = x == e; if(r) {x = d;} else {v = x;}}', where 'cond-update-stmt' can have one of the following forms: 'if(expr ordop x) {x = expr;}', 'if(x ordop expr) {x = expr;}', 'if(x == e) {x = d;}', or 'if(e == x) {x = d;}' where 'x' is an lvalue expression with scalar type, 'expr', 'e', and 'd' are expressions with scalar type, and 'ordop' is one of '<' or '>'.}}
+// omp51-note@+2 {{expected compound statement}}
+#pragma omp atomic compare capture
+  { r = x == e; if (r) { x = d; } else {} }
+// omp51-error@+7 {{the statement for 'atomic compare capture' must be a compound statement of form '{v = x; cond-up-stmt}', ''{cond-up-stmt v = x;}', '{if(x == e) {x = d;} else {v = x;}}', '{r = x == e; if(r) {x = d;}}', or '{r = x == e; if(r) {x = d;} else {v = x;}}', where 'cond-update-stmt' can have one of the following forms: 'if(expr ordop x) {x = expr;}', 'if(x ordop expr) {x = expr;}', 'if(x == e) {x = d;}', or 'if(e == x) {x = d;}' where 'x' is an lvalue expression with scalar type, 'expr', 'e', and 'd' are expressions with scalar type, and 'ordop' is one of '<' or '>'.}}
+// omp51-note@+6 {{expected exactly one expression statement}}
+#pragma omp atomic compare capture
+  {
+    r = x == e;
+    if (r) {
+      x = d;
+    } else {
+      v = x;
+      d = e;
+    }
+  }
+// omp51-error@+3 {{the statement for 'atomic compare capture' must be a compound statement of form '{v = x; cond-up-stmt}', ''{cond-up-stmt v = x;}', '{if(x == e) {x = d;} else {v = x;}}', '{r = x == e; if(r) {x = d;}}', or '{r = x == e; if(r) {x = d;} else {v = x;}}', where 'cond-update-stmt' can have one of the following forms: 'if(expr ordop x) {x = expr;}', 'if(x ordop expr) {x = expr;}', 'if(x == e) {x = d;}', or 'if(e == x) {x = d;}' where 'x' is an lvalue expression with scalar type, 'expr', 'e', and 'd' are expressions with scalar type, and 'ordop' is one of '<' or '>'.}}
+// omp51-note@+2 {{expected assignment statement}}
+#pragma omp atomic compare capture
+  { r = x == e; if (r) { x = d; } else { bbar(); } }
+// omp51-error@+3 {{the statement for 'atomic compare capture' must be a compound statement of form '{v = x; cond-up-stmt}', ''{cond-up-stmt v = x;}', '{if(x == e) {x = d;} else {v = x;}}', '{r = x == e; if(r) {x = d;}}', or '{r = x == e; if(r) {x = d;} else {v = x;}}', where 'cond-update-stmt' can have one of the following forms: 'if(expr ordop x) {x = expr;}', 'if(x ordop expr) {x = expr;}', 'if(x == e) {x = d;}', or 'if(e == x) {x = d;}' where 'x' is an lvalue expression with scalar type, 'expr', 'e', and 'd' are expressions with scalar type, and 'ordop' is one of '<' or '>'.}}
+// omp51-note@+2 {{expected assignment statement}}
+#pragma omp atomic compare capture
+  { r = x == e; if (r) { x = d; } else { v += x; } }
+// omp51-error@+3 {{the statement for 'atomic compare capture' must be a compound statement of form '{v = x; cond-up-stmt}', ''{cond-up-stmt v = x;}', '{if(x == e) {x = d;} else {v = x;}}', '{r = x == e; if(r) {x = d;}}', or '{r = x == e; if(r) {x = d;} else {v = x;}}', where 'cond-update-stmt' can have one of the following forms: 'if(expr ordop x) {x = expr;}', 'if(x ordop expr) {x = expr;}', 'if(x == e) {x = d;}', or 'if(e == x) {x = d;}' where 'x' is an lvalue expression with scalar type, 'expr', 'e', and 'd' are expressions with scalar type, and 'ordop' is one of '<' or '>'.}}
+// omp51-note@+2 {{expect an assignment statement 'v = x'}}
+#pragma omp atomic compare capture
+  { r = x == e; if (r) { x = d; } else { v = d; } }
+// omp51-error@+3 {{the statement for 'atomic compare capture' must be a compound statement of form '{v = x; cond-up-stmt}', ''{cond-up-stmt v = x;}', '{if(x == e) {x = d;} else {v = x;}}', '{r = x == e; if(r) {x = d;}}', or '{r = x == e; if(r) {x = d;} else {v = x;}}', where 'cond-update-stmt' can have one of the following forms: 'if(expr ordop x) {x = expr;}', 'if(x ordop expr) {x = expr;}', 'if(x == e) {x = d;}', or 'if(e == x) {x = d;}' where 'x' is an lvalue expression with scalar type, 'expr', 'e', and 'd' are expressions with scalar type, and 'ordop' is one of '<' or '>'.}}
+// omp51-note@+2 {{expected assignment statement}}
+#pragma omp atomic compare capture
+  { v += x; if (x == e) { x = d; } }
+// omp51-error@+3 {{the statement for 'atomic compare capture' must be a compound statement of form '{v = x; cond-up-stmt}', ''{cond-up-stmt v = x;}', '{if(x == e) {x = d;} else {v = x;}}', '{r = x == e; if(r) {x = d;}}', or '{r = x == e; if(r) {x = d;} else {v = x;}}', where 'cond-update-stmt' can have one of the following forms: 'if(expr ordop x) {x = expr;}', 'if(x ordop expr) {x = expr;}', 'if(x == e) {x = d;}', or 'if(e == x) {x = d;}' where 'x' is an lvalue expression with scalar type, 'expr', 'e', and 'd' are expressions with scalar type, and 'ordop' is one of '<' or '>'.}}
+// omp51-note@+2 {{expected assignment statement}}
+#pragma omp atomic compare capture
+  { if (x == e) { x = d; } v += x; }
+// omp51-error@+3 {{the statement for 'atomic compare capture' must be a compound statement of form '{v = x; cond-up-stmt}', ''{cond-up-stmt v = x;}', '{if(x == e) {x = d;} else {v = x;}}', '{r = x == e; if(r) {x = d;}}', or '{r = x == e; if(r) {x = d;} else {v = x;}}', where 'cond-update-stmt' can have one of the following forms: 'if(expr ordop x) {x = expr;}', 'if(x ordop expr) {x = expr;}', 'if(x == e) {x = d;}', or 'if(e == x) {x = d;}' where 'x' is an lvalue expression with scalar type, 'expr', 'e', and 'd' are expressions with scalar type, and 'ordop' is one of '<' or '>'.}}
+// omp51-note@+2 {{expect an assignment statement 'v = x'}}
+#pragma omp atomic compare capture
+  { v = d; if (x == e) { x = d; } }
+// omp51-error@+3 {{the statement for 'atomic compare capture' must be a compound statement of form '{v = x; cond-up-stmt}', ''{cond-up-stmt v = x;}', '{if(x == e) {x = d;} else {v = x;}}', '{r = x == e; if(r) {x = d;}}', or '{r = x == e; if(r) {x = d;} else {v = x;}}', where 'cond-update-stmt' can have one of the following forms: 'if(expr ordop x) {x = expr;}', 'if(x ordop expr) {x = expr;}', 'if(x == e) {x = d;}', or 'if(e == x) {x = d;}' where 'x' is an lvalue expression with scalar type, 'expr', 'e', and 'd' are expressions with scalar type, and 'ordop' is one of '<' or '>'.}}
+// omp51-note@+2 {{expect an assignment statement 'v = x'}}
+#pragma omp atomic compare capture
+  { if (x == e) { x = d; } v = d; }
+// omp51-error@+3 {{the statement for 'atomic compare capture' must be a compound statement of form '{v = x; cond-up-stmt}', ''{cond-up-stmt v = x;}', '{if(x == e) {x = d;} else {v = x;}}', '{r = x == e; if(r) {x = d;}}', or '{r = x == e; if(r) {x = d;} else {v = x;}}', where 'cond-update-stmt' can have one of the following forms: 'if(expr ordop x) {x = expr;}', 'if(x ordop expr) {x = expr;}', 'if(x == e) {x = d;}', or 'if(e == x) {x = d;}' where 'x' is an lvalue expression with scalar type, 'expr', 'e', and 'd' are expressions with scalar type, and 'ordop' is one of '<' or '>'.}}
+// omp51-note@+2 {{expect a 'if' statement}}
+#pragma omp atomic compare capture
+  { v = x; bbar(); }
+
+  float fv;
+// omp51-error@+3 {{the statement for 'atomic compare capture' must be a compound statement of form '{v = x; cond-up-stmt}', ''{cond-up-stmt v = x;}', '{if(x == e) {x = d;} else {v = x;}}', '{r = x == e; if(r) {x = d;}}', or '{r = x == e; if(r) {x = d;} else {v = x;}}', where 'cond-update-stmt' can have one of the following forms: 'if(expr ordop x) {x = expr;}', 'if(x ordop expr) {x = expr;}', 'if(x == e) {x = d;}', or 'if(e == x) {x = d;}' where 'x' is an lvalue expression with scalar type, 'expr', 'e', and 'd' are expressions with scalar type, and 'ordop' is one of '<' or '>'.}}
+// omp51-note@+2 {{expect integer value}}
+#pragma omp atomic compare capture
+  { fv = x; if (x == e) { x = d; } }
+}
 #endif
diff --git a/clang/test/OpenMP/atomic_messages.cpp b/clang/test/OpenMP/atomic_messages.cpp
index 700c86da1a588..23fd24bfcf118 100644
--- a/clang/test/OpenMP/atomic_messages.cpp
+++ b/clang/test/OpenMP/atomic_messages.cpp
@@ -928,7 +928,7 @@ T mixed() {
 }
 
 int mixed() {
-  int a, b = 0;
+  int a, v, b = 0;
 // expected-error@+2 {{directive '#pragma omp atomic' cannot contain more than one 'read', 'write', 'update', 'capture', or 'compare' clause}}
 // expected-note@+1 {{'read' clause used here}}
 #pragma omp atomic read write
@@ -957,7 +957,7 @@ int mixed() {
 // expected-error@+2 {{directive '#pragma omp atomic' cannot contain more than one 'compare' clause}}
 // expected-error@+1 {{directive '#pragma omp atomic' cannot contain more than one 'capture' clause}}
 #pragma omp atomic compare compare capture capture
-  a = b;
+  { v = a; if (a > b) a = b; }
 #endif
   // expected-note@+1 {{in instantiation of function template specialization 'mixed<int>' requested here}}
   return mixed<int>();