Index: include/clang/Basic/Attr.td
===================================================================
--- include/clang/Basic/Attr.td	(revision 214227)
+++ include/clang/Basic/Attr.td	(working copy)
@@ -1784,13 +1784,19 @@
 }
 
 def LoopHint : Attr {
-  /// vectorize: vectorizes loop operations if 'value != 0'.
-  /// vectorize_width: vectorize loop operations with width 'value'.
-  /// interleave: interleave multiple loop iterations if 'value != 0'.
-  /// interleave_count: interleaves 'value' loop interations.
-  /// unroll: fully unroll loop if 'value != 0'.
-  /// unroll_count: unrolls loop 'value' times.
+  /// #pragma clang loop <option> directive
+  /// vectorize: vectorizes loop operations if State == Enable.
+  /// vectorize_width: vectorize loop operations with width 'Value'.
+  /// interleave: interleave multiple loop iterations if State == Enable.
+  /// interleave_count: interleaves 'Value' loop interations.
+  /// unroll: fully unroll loop if State == Enable.
+  /// unroll_count: unrolls loop 'Value' times.
 
+  /// #pragma unroll <argument> directive
+  /// <no arg>: fully unrolls loop.
+  /// boolean: fully unrolls loop if State == Enable.
+  /// expression: unrolls loop 'Value' times.
+
   let Spellings = [Pragma<"clang", "loop">, Pragma<"", "unroll">,
                    Pragma<"", "nounroll">];
 
@@ -1800,6 +1806,9 @@
                            "unroll", "unroll_count"],
                           ["Vectorize", "VectorizeWidth", "Interleave", "InterleaveCount",
                            "Unroll", "UnrollCount"]>,
+              EnumArgument<"State", "StateType",
+                           ["default", "enable", "disable"],
+                           ["Default", "Enable", "Disable"]>,
               DefaultIntArgument<"Value", 1>];
 
   let AdditionalMembers = [{
@@ -1841,9 +1850,9 @@
     if (option == VectorizeWidth || option == InterleaveCount ||
         option == UnrollCount)
       OS << value;
-    else if (value < 0)
+    else if (state == Default)
       return "";
-    else if (value > 0)
+    else if (state == Enable)
       OS << (option == Unroll ? "full" : "enable");
     else
       OS << "disable";
Index: include/clang/Basic/DiagnosticParseKinds.td
===================================================================
--- include/clang/Basic/DiagnosticParseKinds.td	(revision 214227)
+++ include/clang/Basic/DiagnosticParseKinds.td	(working copy)
@@ -917,10 +917,16 @@
 def err_omp_expected_identifier_for_critical : Error<
   "expected identifier specifying the name of the 'omp critical' directive">;
 
+// Pragma support.
+def err_pragma_invalid_keyword : Error<
+  "%select{invalid|missing}0 argument; expected '%select{enable|full}1' or 'disable'">;
+
 // Pragma loop support.
 def err_pragma_loop_invalid_option : Error<
   "%select{invalid|missing}0 option%select{ %1|}0; expected vectorize, "
   "vectorize_width, interleave, interleave_count, unroll, or unroll_count">;
+def err_pragma_loop_numeric_value : Error<
+  "invalid argument; expected a positive integer value">;
 
 // Pragma unroll support.
 def warn_pragma_unroll_cuda_value_in_parens : Warning<
Index: include/clang/Basic/DiagnosticSemaKinds.td
===================================================================
--- include/clang/Basic/DiagnosticSemaKinds.td	(revision 214227)
+++ include/clang/Basic/DiagnosticSemaKinds.td	(working copy)
@@ -541,8 +541,6 @@
   "surrounding namespace with visibility attribute starts here">;
 def err_pragma_loop_invalid_value : Error<
   "invalid argument; expected a positive integer value">;
-def err_pragma_loop_invalid_keyword : Error<
-  "invalid argument; expected '%0' or 'disable'">;
 def err_pragma_loop_compatibility : Error<
   "%select{incompatible|duplicate}0 directives '%1' and '%2'">;
 def err_pragma_loop_precedes_nonloop : Error<
Index: include/clang/Parse/Parser.h
===================================================================
--- include/clang/Parse/Parser.h	(revision 214227)
+++ include/clang/Parse/Parser.h	(working copy)
@@ -525,7 +525,7 @@
 
   /// \brief Handle the annotation token produced for
   /// #pragma clang loop and #pragma unroll.
-  LoopHint HandlePragmaLoopHint();
+  bool HandlePragmaLoopHint(LoopHint &);
 
   /// GetLookAheadToken - This peeks ahead N tokens and returns that token
   /// without consuming any tokens.  LookAhead(0) returns 'Tok', LookAhead(1)
Index: include/clang/Sema/LoopHint.h
===================================================================
--- include/clang/Sema/LoopHint.h	(revision 214227)
+++ include/clang/Sema/LoopHint.h	(working copy)
@@ -29,11 +29,15 @@
   // "#pragma unroll" and "#pragma nounroll" cases, this is identical to
   // PragmaNameLoc.
   IdentifierLoc *OptionLoc;
-  // Identifier for the hint argument.  If null, then the hint has no argument
-  // such as for "#pragma unroll".
-  IdentifierLoc *ValueLoc;
+  // Identifier for the hint state argument.  If null, then the state is
+  // default value such as for "#pragma unroll".
+  IdentifierLoc *StateLoc;
   // Expression for the hint argument if it exists, null otherwise.
   Expr *ValueExpr;
+
+  LoopHint()
+      : PragmaNameLoc(nullptr), OptionLoc(nullptr), StateLoc(nullptr),
+        ValueExpr(nullptr) {}
 };
 
 } // end namespace clang
Index: lib/CodeGen/CGStmt.cpp
===================================================================
--- lib/CodeGen/CGStmt.cpp	(revision 214227)
+++ lib/CodeGen/CGStmt.cpp	(working copy)
@@ -588,6 +588,7 @@
       continue;
 
     LoopHintAttr::OptionType Option = LH->getOption();
+    int State = LH->getState();
     int ValueInt = LH->getValue();
 
     const char *MetadataName;
@@ -602,8 +603,8 @@
       break;
     case LoopHintAttr::Unroll:
       // With the unroll loop hint, a non-zero value indicates full unrolling.
-      MetadataName =
-          ValueInt == 0 ? "llvm.loop.unroll.disable" : "llvm.loop.unroll.full";
+      MetadataName = State == LoopHintAttr::Disable ? "llvm.loop.unroll.disable"
+                                                    : "llvm.loop.unroll.full";
       break;
     case LoopHintAttr::UnrollCount:
       MetadataName = "llvm.loop.unroll.count";
@@ -614,7 +615,7 @@
     switch (Option) {
     case LoopHintAttr::Vectorize:
     case LoopHintAttr::Interleave:
-      if (ValueInt == 1) {
+      if (State != LoopHintAttr::Disable) {
         // FIXME: In the future I will modifiy the behavior of the metadata
         // so we can enable/disable vectorization and interleaving separately.
         Name = llvm::MDString::get(Context, "llvm.loop.vectorize.enable");
Index: lib/Parse/ParsePragma.cpp
===================================================================
--- lib/Parse/ParsePragma.cpp	(revision 214227)
+++ lib/Parse/ParsePragma.cpp	(working copy)
@@ -722,38 +722,62 @@
   bool HasValue;
 };
 
-LoopHint Parser::HandlePragmaLoopHint() {
+bool Parser::HandlePragmaLoopHint(LoopHint &Hint) {
   assert(Tok.is(tok::annot_pragma_loop_hint));
   PragmaLoopHintInfo *Info =
       static_cast<PragmaLoopHintInfo *>(Tok.getAnnotationValue());
+  ConsumeToken(); // The annotation token.
 
-  LoopHint Hint;
-  Hint.PragmaNameLoc =
-      IdentifierLoc::create(Actions.Context, Info->PragmaName.getLocation(),
-                            Info->PragmaName.getIdentifierInfo());
-  Hint.OptionLoc =
-      IdentifierLoc::create(Actions.Context, Info->Option.getLocation(),
-                            Info->Option.getIdentifierInfo());
-  if (Info->HasValue) {
-    Hint.Range =
-        SourceRange(Info->Option.getLocation(), Info->Value.getLocation());
-    Hint.ValueLoc =
-        IdentifierLoc::create(Actions.Context, Info->Value.getLocation(),
-                              Info->Value.getIdentifierInfo());
+  IdentifierInfo *PragmaNameInfo = Info->PragmaName.getIdentifierInfo();
+  Hint.PragmaNameLoc = IdentifierLoc::create(
+      Actions.Context, Info->PragmaName.getLocation(), PragmaNameInfo);
 
+  IdentifierInfo *OptionInfo = Info->Option.getIdentifierInfo();
+  Hint.OptionLoc = IdentifierLoc::create(
+      Actions.Context, Info->Option.getLocation(), OptionInfo);
+
+  bool PragmaUnroll = PragmaNameInfo->getName() == "unroll";
+  bool PragmaNoUnroll = PragmaNameInfo->getName() == "nounroll";
+  if (!Info->HasValue && (PragmaUnroll | PragmaNoUnroll)) {
+    Hint.Range = SourceRange(Info->PragmaName.getLocation());
+    return true;
+  }
+
+  bool StateOption = false;
+  if (OptionInfo) // Pragma unroll does not specify an option.
+    StateOption = llvm::StringSwitch<bool>(OptionInfo->getName())
+                      .Case("vectorize", true)
+                      .Case("interleave", true)
+                      .Case("unroll", true)
+                      .Default(false);
+
+  // Validate the argument.
+  if (StateOption) {
+    bool OptionUnroll = OptionInfo->isStr("unroll");
+    SourceLocation StateLoc = Info->Value.getLocation();
+    IdentifierInfo *StateInfo = Info->Value.getIdentifierInfo();
+    if (!StateInfo || ((OptionUnroll ? !StateInfo->isStr("full")
+                                     : !StateInfo->isStr("enable")) &&
+                       !StateInfo->isStr("disable"))) {
+      Diag(StateLoc, diag::err_pragma_invalid_keyword)
+          << /*MissingArgument=*/false << /*FullKeyword=*/OptionUnroll;
+      return false;
+    }
+    Hint.StateLoc = IdentifierLoc::create(Actions.Context, StateLoc, StateInfo);
+  } else {
     // FIXME: We should allow non-type template parameters for the loop hint
     // value. See bug report #19610
     if (Info->Value.is(tok::numeric_constant))
       Hint.ValueExpr = Actions.ActOnNumericConstant(Info->Value).get();
-    else
-      Hint.ValueExpr = nullptr;
-  } else {
-    Hint.Range = SourceRange(Info->PragmaName.getLocation());
-    Hint.ValueLoc = nullptr;
-    Hint.ValueExpr = nullptr;
+    else {
+      Diag(Info->Value.getLocation(), diag::err_pragma_loop_numeric_value);
+      return false;
+    }
   }
 
-  return Hint;
+  Hint.Range = SourceRange(Info->PragmaName.getLocation(),
+                           Info->Value.getLocation());
+  return true;
 }
 
 // #pragma GCC visibility comes in two variants:
@@ -1755,12 +1779,10 @@
 }
 
 /// \brief Parses loop or unroll pragma hint value and fills in Info.
-static bool ParseLoopHintValue(Preprocessor &PP, Token Tok, Token &PragmaName,
-                               Token &Option, bool &ValueInParens,
+static bool ParseLoopHintValue(Preprocessor &PP, Token &Tok, Token PragmaName,
+                               Token Option, bool ValueInParens,
                                PragmaLoopHintInfo &Info) {
-  ValueInParens = Tok.is(tok::l_paren);
   if (ValueInParens) {
-    PP.Lex(Tok);
     if (Tok.is(tok::r_paren)) {
       // Nothing between the parentheses.
       std::string PragmaString;
@@ -1784,13 +1806,15 @@
 
   // FIXME: Value should be stored and parsed as a constant expression.
   Token Value = Tok;
+  PP.Lex(Tok);
 
   if (ValueInParens) {
-    PP.Lex(Tok);
+    // Read ')'
     if (Tok.isNot(tok::r_paren)) {
       PP.Diag(Tok.getLocation(), diag::err_expected) << tok::r_paren;
       return true;
     }
+    PP.Lex(Tok);
   }
 
   Info.PragmaName = PragmaName;
@@ -1872,18 +1896,19 @@
           << /*MissingOption=*/false << OptionInfo;
       return;
     }
-
-    auto *Info = new (PP.getPreprocessorAllocator()) PragmaLoopHintInfo;
     PP.Lex(Tok);
-    bool ValueInParens;
-    if (ParseLoopHintValue(PP, Tok, PragmaName, Option, ValueInParens, *Info))
-      return;
 
-    if (!ValueInParens) {
-      PP.Diag(Info->Value.getLocation(), diag::err_expected) << tok::l_paren;
+    // Read '('
+    if (Tok.isNot(tok::l_paren)) {
+      PP.Diag(Tok.getLocation(), diag::err_expected) << tok::l_paren;
       return;
     }
+    PP.Lex(Tok);
 
+    auto *Info = new (PP.getPreprocessorAllocator()) PragmaLoopHintInfo;
+    if (ParseLoopHintValue(PP, Tok, PragmaName, Option, /*ValueInParens=*/true, *Info))
+      return;
+
     // Generate the loop hint token.
     Token LoopHintTok;
     LoopHintTok.startToken();
@@ -1891,9 +1916,6 @@
     LoopHintTok.setLocation(PragmaName.getLocation());
     LoopHintTok.setAnnotationValue(static_cast<void *>(Info));
     TokenList.push_back(LoopHintTok);
-
-    // Get next optimization option.
-    PP.Lex(Tok);
   }
 
   if (Tok.isNot(tok::eod)) {
@@ -1938,7 +1960,6 @@
   if (Tok.is(tok::eod)) {
     // nounroll or unroll pragma without an argument.
     Info->PragmaName = PragmaName;
-    Info->Option = PragmaName;
     Info->HasValue = false;
   } else if (PragmaName.getIdentifierInfo()->getName() == "nounroll") {
     PP.Diag(Tok.getLocation(), diag::warn_pragma_extra_tokens_at_eol)
@@ -1947,9 +1968,12 @@
   } else {
     // Unroll pragma with an argument: "#pragma unroll N" or
     // "#pragma unroll(N)".
-    bool ValueInParens;
-    if (ParseLoopHintValue(PP, Tok, PragmaName, PragmaName, ValueInParens,
-                           *Info))
+    // Read '(' if it exists.
+    bool ValueInParens = Tok.is(tok::l_paren);
+    if (ValueInParens)
+      PP.Lex(Tok);
+
+    if (ParseLoopHintValue(PP, Tok, PragmaName, Token(), ValueInParens, *Info))
       return;
 
     // In CUDA, the argument to '#pragma unroll' should not be contained in
@@ -1958,7 +1982,6 @@
       PP.Diag(Info->Value.getLocation(),
               diag::warn_pragma_unroll_cuda_value_in_parens);
 
-    PP.Lex(Tok);
     if (Tok.isNot(tok::eod)) {
       PP.Diag(Tok.getLocation(), diag::warn_pragma_extra_tokens_at_eol)
           << "unroll";
Index: lib/Parse/ParseStmt.cpp
===================================================================
--- lib/Parse/ParseStmt.cpp	(revision 214227)
+++ lib/Parse/ParseStmt.cpp	(working copy)
@@ -1817,10 +1817,11 @@
 
   // Get loop hints and consume annotated token.
   while (Tok.is(tok::annot_pragma_loop_hint)) {
-    LoopHint Hint = HandlePragmaLoopHint();
-    ConsumeToken();
+    LoopHint Hint;
+    if (!HandlePragmaLoopHint(Hint))
+      continue;
 
-    ArgsUnion ArgHints[] = {Hint.PragmaNameLoc, Hint.OptionLoc, Hint.ValueLoc,
+    ArgsUnion ArgHints[] = {Hint.PragmaNameLoc, Hint.OptionLoc, Hint.StateLoc,
                             ArgsUnion(Hint.ValueExpr)};
     TempAttrs.addNew(Hint.PragmaNameLoc->Ident, Hint.Range, nullptr,
                      Hint.PragmaNameLoc->Loc, ArgHints, 4,
Index: lib/Sema/SemaStmtAttr.cpp
===================================================================
--- lib/Sema/SemaStmtAttr.cpp	(revision 214227)
+++ lib/Sema/SemaStmtAttr.cpp	(working copy)
@@ -47,13 +47,11 @@
                                 SourceRange) {
   IdentifierLoc *PragmaNameLoc = A.getArgAsIdent(0);
   IdentifierLoc *OptionLoc = A.getArgAsIdent(1);
-  IdentifierInfo *OptionInfo = OptionLoc->Ident;
-  IdentifierLoc *ValueLoc = A.getArgAsIdent(2);
-  IdentifierInfo *ValueInfo = ValueLoc ? ValueLoc->Ident : nullptr;
+  IdentifierLoc *StateLoc = A.getArgAsIdent(2);
   Expr *ValueExpr = A.getArgAsExpr(3);
 
-  assert(OptionInfo && "Attribute must have valid option info.");
-
+  bool PragmaUnroll = PragmaNameLoc->Ident->getName() == "unroll";
+  bool PragmaNoUnroll = PragmaNameLoc->Ident->getName() == "nounroll";
   if (St->getStmtClass() != Stmt::DoStmtClass &&
       St->getStmtClass() != Stmt::ForStmtClass &&
       St->getStmtClass() != Stmt::CXXForRangeStmtClass &&
@@ -69,13 +67,16 @@
 
   LoopHintAttr::OptionType Option;
   LoopHintAttr::Spelling Spelling;
-  if (PragmaNameLoc->Ident->getName() == "unroll") {
-    Option = ValueLoc ? LoopHintAttr::UnrollCount : LoopHintAttr::Unroll;
+  if (PragmaUnroll) {
+    Option = ValueExpr ? LoopHintAttr::UnrollCount : LoopHintAttr::Unroll;
     Spelling = LoopHintAttr::Pragma_unroll;
-  } else if (PragmaNameLoc->Ident->getName() == "nounroll") {
+  } else if (PragmaNoUnroll) {
     Option = LoopHintAttr::Unroll;
     Spelling = LoopHintAttr::Pragma_nounroll;
   } else {
+    assert(OptionLoc && OptionLoc->Ident &&
+           "Attribute must have valid option info.");
+    IdentifierInfo *OptionInfo = OptionLoc->Ident;
     Option = llvm::StringSwitch<LoopHintAttr::OptionType>(OptionInfo->getName())
                  .Case("vectorize", LoopHintAttr::Vectorize)
                  .Case("vectorize_width", LoopHintAttr::VectorizeWidth)
@@ -87,35 +88,10 @@
     Spelling = LoopHintAttr::Pragma_clang_loop;
   }
 
-  int ValueInt = -1;
-  if (Option == LoopHintAttr::Unroll &&
-      Spelling == LoopHintAttr::Pragma_unroll) {
-    if (ValueInfo)
-      ValueInt = (ValueInfo->isStr("disable") ? 0 : 1);
-  } else if (Option == LoopHintAttr::Unroll &&
-             Spelling == LoopHintAttr::Pragma_nounroll) {
-    ValueInt = 0;
-  } else if (Option == LoopHintAttr::Vectorize ||
-             Option == LoopHintAttr::Interleave ||
-             Option == LoopHintAttr::Unroll) {
-    // Unrolling uses the keyword "full" rather than "enable" to indicate full
-    // unrolling.
-    const char *TrueKeyword =
-        Option == LoopHintAttr::Unroll ? "full" : "enable";
-    if (!ValueInfo) {
-      S.Diag(ValueLoc->Loc, diag::err_pragma_loop_invalid_keyword)
-          << TrueKeyword;
-      return nullptr;
-    }
-    if (ValueInfo->isStr("disable"))
-      ValueInt = 0;
-    else if (ValueInfo->getName() == TrueKeyword)
-      ValueInt = 1;
-    else {
-      S.Diag(ValueLoc->Loc, diag::err_pragma_loop_invalid_keyword)
-          << TrueKeyword;
-      return nullptr;
-    }
+  int ValueInt = 1;
+  LoopHintAttr::StateType State = LoopHintAttr::Default;
+  if (PragmaNoUnroll) {
+    State = LoopHintAttr::Disable;
   } else if (Option == LoopHintAttr::VectorizeWidth ||
              Option == LoopHintAttr::InterleaveCount ||
              Option == LoopHintAttr::UnrollCount) {
@@ -124,28 +100,39 @@
     llvm::APSInt ValueAPS;
     if (!ValueExpr || !ValueExpr->isIntegerConstantExpr(ValueAPS, S.Context) ||
         (ValueInt = ValueAPS.getSExtValue()) < 1) {
-      S.Diag(ValueLoc->Loc, diag::err_pragma_loop_invalid_value);
+      S.Diag(A.getRange().getEnd(), diag::err_pragma_loop_invalid_value);
       return nullptr;
     }
-  } else
-    llvm_unreachable("Unknown loop hint option");
+  } else if (Option == LoopHintAttr::Vectorize ||
+             Option == LoopHintAttr::Interleave ||
+             Option == LoopHintAttr::Unroll) {
+    // Default state is assumed if StateLoc is not specified, such as with
+    // '#pragma unroll'.
+    if (StateLoc && StateLoc->Ident) {
+      if (StateLoc->Ident->isStr("disable"))
+        State = LoopHintAttr::Disable;
+      else
+        State = LoopHintAttr::Enable;
+    }
+  }
 
-  return LoopHintAttr::CreateImplicit(S.Context, Spelling, Option, ValueInt,
-                                      A.getRange());
+  return LoopHintAttr::CreateImplicit(S.Context, Spelling, Option, State,
+                                      ValueInt, A.getRange());
 }
 
-static void CheckForIncompatibleAttributes(
-    Sema &S, const SmallVectorImpl<const Attr *> &Attrs) {
-  // There are 3 categories of loop hints attributes: vectorize, interleave, and
-  // unroll. Each comes in two variants: a boolean form and a numeric form.  The
-  // boolean hints selectively enables/disables the transformation for the loop
-  // (for unroll, a nonzero value indicates full unrolling rather than enabling
-  // the transformation).  The numeric hint provides an integer hint (for
-  // example, unroll count) to the transformer. The following array accumulates
-  // the hints encountered while iterating through the attributes to check for
-  // compatibility.
+static void
+CheckForIncompatibleAttributes(Sema &S,
+                               const SmallVectorImpl<const Attr *> &Attrs) {
+  // There are 3 categories of loop hints attributes: vectorize, interleave,
+  // and unroll. Each comes in two variants: a state form and a numeric form.
+  // The state form selectively defaults/enables/disables the transformation
+  // for the loop (for unroll, default indicates full unrolling rather than
+  // enabling the transformation).  The numeric form form provides an integer
+  // hint (for example, unroll count) to the transformer. The following array
+  // accumulates the hints encountered while iterating through the attributes
+  // to check for compatibility.
   struct {
-    const LoopHintAttr *EnableAttr;
+    const LoopHintAttr *StateAttr;
     const LoopHintAttr *NumericAttr;
   } HintAttrs[] = {{nullptr, nullptr}, {nullptr, nullptr}, {nullptr, nullptr}};
 
@@ -179,8 +166,8 @@
     if (Option == LoopHintAttr::Vectorize ||
         Option == LoopHintAttr::Interleave || Option == LoopHintAttr::Unroll) {
       // Enable|disable hint.  For example, vectorize(enable).
-      PrevAttr = CategoryState.EnableAttr;
-      CategoryState.EnableAttr = LH;
+      PrevAttr = CategoryState.StateAttr;
+      CategoryState.StateAttr = LH;
     } else {
       // Numeric hint.  For example, vectorize_width(8).
       PrevAttr = CategoryState.NumericAttr;
@@ -195,14 +182,15 @@
           << /*Duplicate=*/true << PrevAttr->getDiagnosticName(Policy)
           << LH->getDiagnosticName(Policy);
 
-    if (CategoryState.EnableAttr && CategoryState.NumericAttr &&
-        (Category == Unroll || !CategoryState.EnableAttr->getValue())) {
+    if (CategoryState.StateAttr && CategoryState.NumericAttr &&
+        (Category == Unroll ||
+         CategoryState.StateAttr->getState() == LoopHintAttr::Disable)) {
       // Disable hints are not compatible with numeric hints of the same
       // category.  As a special case, numeric unroll hints are also not
       // compatible with "enable" form of the unroll pragma, unroll(full).
       S.Diag(OptionLoc, diag::err_pragma_loop_compatibility)
           << /*Duplicate=*/false
-          << CategoryState.EnableAttr->getDiagnosticName(Policy)
+          << CategoryState.StateAttr->getDiagnosticName(Policy)
           << CategoryState.NumericAttr->getDiagnosticName(Policy);
     }
   }