Index: clang/include/clang/Basic/Attr.td
===================================================================
--- clang/include/clang/Basic/Attr.td
+++ clang/include/clang/Basic/Attr.td
@@ -1147,6 +1147,11 @@
   let Documentation = [FallthroughDocs];
 }
 
+def Likely : StmtAttr {
+  let Spellings = [CXX11<"", "likely", 201903>, CXX11<"clang", "likely">];
+  let Documentation = [LikelyDocs];
+}
+
 def FastCall : DeclOrTypeAttr {
   let Spellings = [GCC<"fastcall">, Keyword<"__fastcall">,
                    Keyword<"_fastcall">];
Index: clang/include/clang/Basic/AttrDocs.td
===================================================================
--- clang/include/clang/Basic/AttrDocs.td
+++ clang/include/clang/Basic/AttrDocs.td
@@ -1492,6 +1492,26 @@
   }];
 }
 
+def LikelyDocs : Documentation {
+  let Category = DocCatStmt;
+  let Heading = "likely";
+  let Content = [{
+The ``likely`` (or ``clang::likely``) attribute is used to annotate that a condition is likely to be true
+this is supposed to be used as a hint by the optimizer (not yet implemented)
+
+Here is an example:
+
+.. code-block:: c++
+
+  int f(int i) {
+    if (i == 0) [[likely]]
+      return 1; //indicate that this branch is very likely to be taken
+    return 0;
+  }
+
+  }];
+}
+
 def ARMInterruptDocs : Documentation {
   let Category = DocCatFunction;
   let Heading = "interrupt (ARM)";
Index: clang/include/clang/Basic/DiagnosticSemaKinds.td
===================================================================
--- clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -7339,6 +7339,8 @@
   "use of the %0 attribute is a C++14 extension">, InGroup<CXX14>;
 def ext_cxx17_attr : Extension<
   "use of the %0 attribute is a C++17 extension">, InGroup<CXX17>;
+def ext_cxx2a_attr : Extension<
+  "use of the %0 attribute is a C++2a extension">, InGroup<CXX2a>;
 
 def warn_unused_comparison : Warning<
   "%select{equality|inequality|relational|three-way}0 comparison result unused">,
@@ -8158,6 +8160,9 @@
   "fallthrough annotation in unreachable code">,
   InGroup<ImplicitFallthrough>, DefaultIgnore;
 
+def err_likely_attr_invalid_placement : Error<
+  "likely annotation can't appear here">;
+
 def warn_unreachable_default : Warning<
   "default label in switch which covers all enumeration values">,
   InGroup<CoveredSwitchDefault>, DefaultIgnore;
Index: clang/lib/Parse/ParseDeclCXX.cpp
===================================================================
--- clang/lib/Parse/ParseDeclCXX.cpp
+++ clang/lib/Parse/ParseDeclCXX.cpp
@@ -3858,6 +3858,7 @@
   case ParsedAttr::AT_Deprecated:
   case ParsedAttr::AT_FallThrough:
   case ParsedAttr::AT_CXX11NoReturn:
+  case ParsedAttr::AT_Likely:
     return true;
   case ParsedAttr::AT_WarnUnusedResult:
     return !ScopeName && AttrName->getName().equals("nodiscard");
Index: clang/lib/Parse/ParseStmt.cpp
===================================================================
--- clang/lib/Parse/ParseStmt.cpp
+++ clang/lib/Parse/ParseStmt.cpp
@@ -1216,6 +1216,9 @@
                                             : Sema::ConditionKind::Boolean))
     return StmtError();
 
+  ParsedAttributesWithRange Attrs(AttrFactory);
+  MaybeParseCXX11Attributes(Attrs);
+
   llvm::Optional<bool> ConstexprCondition;
   if (IsConstexpr)
     ConstexprCondition = Cond.getKnownValue();
@@ -1314,8 +1317,13 @@
   if (ElseStmt.isInvalid())
     ElseStmt = Actions.ActOnNullStmt(ElseStmtLoc);
 
-  return Actions.ActOnIfStmt(IfLoc, IsConstexpr, InitStmt.get(), Cond,
-                             ThenStmt.get(), ElseLoc, ElseStmt.get());
+  StmtResult Stmt = Actions.ActOnIfStmt(IfLoc, IsConstexpr, InitStmt.get(), Cond,
+                     ThenStmt.get(), ElseLoc, ElseStmt.get());
+
+  if (!Attrs.empty())
+    return Actions.ProcessStmtAttributes(Stmt.get(), Attrs, Attrs.Range);
+
+  return Stmt;
 }
 
 /// ParseSwitchStatement
Index: clang/lib/Sema/SemaStmtAttr.cpp
===================================================================
--- clang/lib/Sema/SemaStmtAttr.cpp
+++ clang/lib/Sema/SemaStmtAttr.cpp
@@ -51,6 +51,21 @@
   return ::new (S.Context) auto(Attr);
 }
 
+static Attr *handleLikelyAttr(Sema &S, Stmt *St, const ParsedAttr &A,
+                                   SourceRange Range) {
+  LikelyAttr Attr(A.getRange(), S.Context,
+                       A.getAttributeSpellingListIndex());
+
+  if (!llvm::isa<IfStmt>(St)) {
+    S.Diag(A.getLoc(), diag::err_likely_attr_invalid_placement) << A.getName();
+  }
+
+  if (!S.getLangOpts().CPlusPlus2a && !A.getScopeName())
+    S.Diag(A.getLoc(), diag::ext_cxx2a_attr) << A.getName();
+
+  return ::new (S.Context) auto(Attr);
+}
+
 static Attr *handleSuppressAttr(Sema &S, Stmt *St, const ParsedAttr &A,
                                 SourceRange Range) {
   if (A.getNumArgs() < 1) {
@@ -336,6 +351,8 @@
     return nullptr;
   case ParsedAttr::AT_FallThrough:
     return handleFallThroughAttr(S, St, A, Range);
+  case ParsedAttr::AT_Likely:
+    return handleLikelyAttr(S, St, A, Range);
   case ParsedAttr::AT_LoopHint:
     return handleLoopHintAttr(S, St, A, Range);
   case ParsedAttr::AT_OpenCLUnrollHint:
Index: clang/test/AST/ast-dump-attr.cpp
===================================================================
--- clang/test/AST/ast-dump-attr.cpp
+++ clang/test/AST/ast-dump-attr.cpp
@@ -23,6 +23,21 @@
 // CHECK-NEXT:   FallThroughAttr
 // CHECK-NEXT:   NullStmt
 
+int TestLikelyAttribute(int i) {
+  if (i == 1) [[likely]] {
+    return 0;
+  } else if (i == 2) [[likely]]
+    return 1;
+  return 2;
+}
+// CHECK:      FunctionDecl{{.*}}TestLikelyAttribute
+// CHECK:      AttributedStmt
+// CHECK-NEXT: LikelyAttr
+// CHECK-NEXT: IfStmt
+// CHECK:      AttributedStmt
+// CHECK-NEXT: LikelyAttr
+// CHECK-NEXT: IfStmt
+
 [[clang::warn_unused_result]] int TestCXX11DeclAttr();
 // CHECK:      FunctionDecl{{.*}}TestCXX11DeclAttr
 // CHECK-NEXT:   WarnUnusedResultAttr