Add loop pragma for Loop Distribution

Summary:
This is similar to other loop pragmas like 'vectorize'.  Currently it
only has state values: distribute(enable) and distribute(disable).  When
one of these is specified the corresponding loop metadata is generated:

  !{!"llvm.loop.distribute.enable", i1 true/false}

As a result, loop distribution will be attempted on the loop even if
Loop Distribution in not enabled globally.  Analogously, with 'disable'
distribution can be turned off for an individual loop even when the pass
is otherwise enabled.

There are some slight differences compared to the existing loop pragmas.

1. There is no 'assume_safety' variant which makes its handling slightly
different from 'vectorize'/'interleave'.

2. Unlike the existing loop pragmas, it does not have a corresponding
numeric pragma like 'vectorize' -> 'vectorize_width'.  So for the
consistency checks in CheckForIncompatibleAttributes we don't need to
check it against other pragmas.  We just need to check for duplicates of
the same pragma.

Reviewers: rsmith, dexonsmith, aaron.ballman

Subscribers: bob.wilson, cfe-commits, hfinkel

Differential Revision: http://reviews.llvm.org/D19403

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@272656 91177308-0d34-0410-b5e6-96231b3b80d8

12 files changed, 139 insertions, 31 deletions

diff --git a/docs/LanguageExtensions.rst b/docs/LanguageExtensions.rst
index c715164461..0b0a4fb925 100644
--- a/docs/LanguageExtensions.rst
+++ b/docs/LanguageExtensions.rst
@@ -2050,9 +2050,9 @@ Extensions for loop hint optimizations
 
 The ``#pragma clang loop`` directive is used to specify hints for optimizing the
 subsequent for, while, do-while, or c++11 range-based for loop. The directive
-provides options for vectorization, interleaving, and unrolling. Loop hints can
-be specified before any loop and will be ignored if the optimization is not safe
-to apply.
+provides options for vectorization, interleaving, unrolling and
+distribution. Loop hints can be specified before any loop and will be ignored if
+the optimization is not safe to apply.
 
 Vectorization and Interleaving
 ------------------------------
@@ -2147,6 +2147,38 @@ to the same code size limit as with ``unroll(enable)``.
 
 Unrolling of a loop can be prevented by specifying ``unroll(disable)``.
 
+Loop Distribution
+-----------------
+
+Loop Distribution allows splitting a loop into multiple loops.  This is
+beneficial for example when the entire loop cannot be vectorized but some of the
+resulting loops can.
+
+If ``distribute(enable))'' is specified and the loop has memory dependencies
+that inhibit vectorization, the compiler will attempt to isolate the offending
+operations into a new loop.  This optimization is not enabled by default, only
+loops marked with the pragma are considered.
+
+.. code-block:: c++
+
+  #pragma clang loop distribute(enable)
+  for (i = 0; i < N; ++i) {
+    S1: A[i + 1] = A[i] + B[i];
+    S2: C[i] = D[i] * E[i];
+  }
+
+This loop will be split into two loops between statements S1 and S2.  The
+second loop containing S2 will be vectorized.
+
+Loop Distribution is currently not enabled by default in the optimizer because
+it can hurt performance in some cases.  For example, instruction-level
+parallelism could be reduced by sequentializing the execution of the
+statements S1 and S2 above.
+
+If Loop Distribution is turned on globally with
+``-mllvm -enable-loop-distribution``, specifying ``distribute(disable)`` can
+be used the disable it on a per-loop basis.
+
 Additional Information
 ----------------------
 
diff --git a/include/clang/Basic/Attr.td b/include/clang/Basic/Attr.td
index 9d1453495d..f483fc3234 100644
--- a/include/clang/Basic/Attr.td
+++ b/include/clang/Basic/Attr.td
@@ -2186,6 +2186,7 @@ def LoopHint : Attr {
   /// interleave_count: interleaves 'Value' loop interations.
   /// unroll: fully unroll loop if State == Enable.
   /// unroll_count: unrolls loop 'Value' times.
+  /// distribute: attempt to distribute loop if State == Enable
 
   /// #pragma unroll <argument> directive
   /// <no arg>: fully unrolls loop.
@@ -2198,9 +2199,9 @@ def LoopHint : Attr {
   /// State of the loop optimization specified by the spelling.
   let Args = [EnumArgument<"Option", "OptionType",
                           ["vectorize", "vectorize_width", "interleave", "interleave_count",
-                           "unroll", "unroll_count"],
+                           "unroll", "unroll_count", "distribute"],
                           ["Vectorize", "VectorizeWidth", "Interleave", "InterleaveCount",
-                           "Unroll", "UnrollCount"]>,
+                           "Unroll", "UnrollCount", "Distribute"]>,
               EnumArgument<"State", "LoopHintState",
                            ["enable", "disable", "numeric", "assume_safety", "full"],
                            ["Enable", "Disable", "Numeric", "AssumeSafety", "Full"]>,
@@ -2215,6 +2216,7 @@ def LoopHint : Attr {
     case InterleaveCount: return "interleave_count";
     case Unroll: return "unroll";
     case UnrollCount: return "unroll_count";
+    case Distribute: return "distribute";
     }
     llvm_unreachable("Unhandled LoopHint option.");
   }
diff --git a/include/clang/Basic/DiagnosticParseKinds.td b/include/clang/Basic/DiagnosticParseKinds.td
index 8059f50c13..48e1a2765d 100644
--- a/include/clang/Basic/DiagnosticParseKinds.td
+++ b/include/clang/Basic/DiagnosticParseKinds.td
@@ -977,12 +977,12 @@ def err_omp_declare_target_unexpected_clause: Error<
 // Pragma loop support.
 def err_pragma_loop_missing_argument : Error<
   "missing argument; expected %select{an integer value|"
-  "'enable', %select{'assume_safety'|'full'}1 or 'disable'}0">;
+  "'enable'%select{|, 'full'}1%select{|, 'assume_safety'}2 or 'disable'}0">;
 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">;
+  "vectorize_width, interleave, interleave_count, unroll, unroll_count, or distribute">;
 def err_pragma_invalid_keyword : Error<
-  "invalid argument; expected 'enable', %select{'assume_safety'|'full'}0 or 'disable'">;
+  "invalid argument; expected 'enable'%select{|, 'full'}0%select{|, 'assume_safety'}1 or 'disable'">;
 
 // Pragma unroll support.
 def warn_pragma_unroll_cuda_value_in_parens : Warning<
diff --git a/lib/CodeGen/CGLoopInfo.cpp b/lib/CodeGen/CGLoopInfo.cpp
index e07fbb9bb3..51474f16a0 100644
--- a/lib/CodeGen/CGLoopInfo.cpp
+++ b/lib/CodeGen/CGLoopInfo.cpp
@@ -26,6 +26,7 @@ static MDNode *createMetadata(LLVMContext &Ctx, const LoopAttributes &Attrs,
       Attrs.InterleaveCount == 0 && Attrs.UnrollCount == 0 &&
       Attrs.VectorizeEnable == LoopAttributes::Unspecified &&
       Attrs.UnrollEnable == LoopAttributes::Unspecified &&
+      Attrs.DistributeEnable == LoopAttributes::Unspecified &&
       !Location)
     return nullptr;
 
@@ -84,6 +85,14 @@ static MDNode *createMetadata(LLVMContext &Ctx, const LoopAttributes &Attrs,
     Args.push_back(MDNode::get(Ctx, Vals));
   }
 
+  if (Attrs.DistributeEnable != LoopAttributes::Unspecified) {
+    Metadata *Vals[] = {MDString::get(Ctx, "llvm.loop.distribute.enable"),
+                        ConstantAsMetadata::get(ConstantInt::get(
+                            Type::getInt1Ty(Ctx), (Attrs.DistributeEnable ==
+                                                   LoopAttributes::Enable)))};
+    Args.push_back(MDNode::get(Ctx, Vals));
+  }
+
   // Set the first operand to itself.
   MDNode *LoopID = MDNode::get(Ctx, Args);
   LoopID->replaceOperandWith(0, LoopID);
@@ -93,7 +102,8 @@ static MDNode *createMetadata(LLVMContext &Ctx, const LoopAttributes &Attrs,
 LoopAttributes::LoopAttributes(bool IsParallel)
     : IsParallel(IsParallel), VectorizeEnable(LoopAttributes::Unspecified),
       UnrollEnable(LoopAttributes::Unspecified), VectorizeWidth(0),
-      InterleaveCount(0), UnrollCount(0) {}
+      InterleaveCount(0), UnrollCount(0),
+      DistributeEnable(LoopAttributes::Unspecified) {}
 
 void LoopAttributes::clear() {
   IsParallel = false;
@@ -172,6 +182,9 @@ void LoopInfoStack::push(BasicBlock *Header, clang::ASTContext &Ctx,
       case LoopHintAttr::Unroll:
         setUnrollState(LoopAttributes::Disable);
         break;
+      case LoopHintAttr::Distribute:
+        setDistributeState(false);
+        break;
       case LoopHintAttr::UnrollCount:
       case LoopHintAttr::VectorizeWidth:
       case LoopHintAttr::InterleaveCount:
@@ -188,6 +201,9 @@ void LoopInfoStack::push(BasicBlock *Header, clang::ASTContext &Ctx,
       case LoopHintAttr::Unroll:
         setUnrollState(LoopAttributes::Enable);
         break;
+      case LoopHintAttr::Distribute:
+        setDistributeState(true);
+        break;
       case LoopHintAttr::UnrollCount:
       case LoopHintAttr::VectorizeWidth:
       case LoopHintAttr::InterleaveCount:
@@ -207,6 +223,7 @@ void LoopInfoStack::push(BasicBlock *Header, clang::ASTContext &Ctx,
       case LoopHintAttr::UnrollCount:
       case LoopHintAttr::VectorizeWidth:
       case LoopHintAttr::InterleaveCount:
+      case LoopHintAttr::Distribute:
         llvm_unreachable("Options cannot be used to assume mem safety.");
         break;
       }
@@ -221,6 +238,7 @@ void LoopInfoStack::push(BasicBlock *Header, clang::ASTContext &Ctx,
       case LoopHintAttr::UnrollCount:
       case LoopHintAttr::VectorizeWidth:
       case LoopHintAttr::InterleaveCount:
+      case LoopHintAttr::Distribute:
         llvm_unreachable("Options cannot be used with 'full' hint.");
         break;
       }
@@ -239,6 +257,7 @@ void LoopInfoStack::push(BasicBlock *Header, clang::ASTContext &Ctx,
       case LoopHintAttr::Unroll:
       case LoopHintAttr::Vectorize:
       case LoopHintAttr::Interleave:
+      case LoopHintAttr::Distribute:
         llvm_unreachable("Options cannot be assigned a value.");
         break;
       }
diff --git a/lib/CodeGen/CGLoopInfo.h b/lib/CodeGen/CGLoopInfo.h
index 7b9980c618..a0111edde5 100644
--- a/lib/CodeGen/CGLoopInfo.h
+++ b/lib/CodeGen/CGLoopInfo.h
@@ -58,6 +58,9 @@ struct LoopAttributes {
 
   /// \brief llvm.unroll.
   unsigned UnrollCount;
+
+  /// \brief Value for llvm.loop.distribute.enable metadata.
+  LVEnableState DistributeEnable;
 };
 
 /// \brief Information used when generating a structured loop.
@@ -130,6 +133,12 @@ public:
         Enable ? LoopAttributes::Enable : LoopAttributes::Disable;
   }
 
+  /// \brief Set the next pushed loop as a distribution candidate.
+  void setDistributeState(bool Enable = true) {
+    StagedAttrs.DistributeEnable =
+        Enable ? LoopAttributes::Enable : LoopAttributes::Disable;
+  }
+
   /// \brief Set the next pushed loop unroll state.
   void setUnrollState(const LoopAttributes::LVEnableState &State) {
     StagedAttrs.UnrollEnable = State;
diff --git a/lib/Parse/ParsePragma.cpp b/lib/Parse/ParsePragma.cpp
index 9e9a749bb9..bff5d1170f 100644
--- a/lib/Parse/ParsePragma.cpp
+++ b/lib/Parse/ParsePragma.cpp
@@ -826,20 +826,25 @@ bool Parser::HandlePragmaLoopHint(LoopHint &Hint) {
 
   // If no option is specified the argument is assumed to be a constant expr.
   bool OptionUnroll = false;
+  bool OptionDistribute = false;
   bool StateOption = false;
   if (OptionInfo) { // Pragma Unroll does not specify an option.
     OptionUnroll = OptionInfo->isStr("unroll");
+    OptionDistribute = OptionInfo->isStr("distribute");
     StateOption = llvm::StringSwitch<bool>(OptionInfo->getName())
                       .Case("vectorize", true)
                       .Case("interleave", true)
-                      .Default(false) || OptionUnroll;
+                      .Default(false) ||
+                  OptionUnroll || OptionDistribute;
   }
 
+  bool AssumeSafetyArg = !OptionUnroll && !OptionDistribute;
   // Verify loop hint has an argument.
   if (Toks[0].is(tok::eof)) {
     ConsumeToken(); // The annotation token.
     Diag(Toks[0].getLocation(), diag::err_pragma_loop_missing_argument)
-        << /*StateArgument=*/StateOption << /*FullKeyword=*/OptionUnroll;
+        << /*StateArgument=*/StateOption << /*FullKeyword=*/OptionUnroll
+        << /*AssumeSafetyKeyword=*/AssumeSafetyArg;
     return false;
   }
 
@@ -853,11 +858,12 @@ bool Parser::HandlePragmaLoopHint(LoopHint &Hint) {
                  llvm::StringSwitch<bool>(StateInfo->getName())
                      .Cases("enable", "disable", true)
                      .Case("full", OptionUnroll)
-                     .Case("assume_safety", !OptionUnroll)
+                     .Case("assume_safety", AssumeSafetyArg)
                      .Default(false);
     if (!Valid) {
       Diag(Toks[0].getLocation(), diag::err_pragma_invalid_keyword)
-          << /*FullKeyword=*/OptionUnroll;
+          << /*FullKeyword=*/OptionUnroll
+          << /*AssumeSafetyKeyword=*/AssumeSafetyArg;
       return false;
     }
     if (Toks.size() > 2)
@@ -2005,6 +2011,7 @@ void PragmaLoopHintHandler::HandlePragma(Preprocessor &PP,
                            .Case("vectorize", true)
                            .Case("interleave", true)
                            .Case("unroll", true)
+                           .Case("distribute", true)
                            .Case("vectorize_width", true)
                            .Case("interleave_count", true)
                            .Case("unroll_count", true)
diff --git a/lib/Sema/SemaStmtAttr.cpp b/lib/Sema/SemaStmtAttr.cpp
index 5120a8773c..87fd889395 100644
--- a/lib/Sema/SemaStmtAttr.cpp
+++ b/lib/Sema/SemaStmtAttr.cpp
@@ -107,6 +107,7 @@ static Attr *handleLoopHintAttr(Sema &S, Stmt *St, const AttributeList &A,
                  .Case("interleave_count", LoopHintAttr::InterleaveCount)
                  .Case("unroll", LoopHintAttr::Unroll)
                  .Case("unroll_count", LoopHintAttr::UnrollCount)
+                 .Case("distribute", LoopHintAttr::Distribute)
                  .Default(LoopHintAttr::Vectorize);
     if (Option == LoopHintAttr::VectorizeWidth ||
         Option == LoopHintAttr::InterleaveCount ||
@@ -117,7 +118,8 @@ static Attr *handleLoopHintAttr(Sema &S, Stmt *St, const AttributeList &A,
       State = LoopHintAttr::Numeric;
     } else if (Option == LoopHintAttr::Vectorize ||
                Option == LoopHintAttr::Interleave ||
-               Option == LoopHintAttr::Unroll) {
+               Option == LoopHintAttr::Unroll ||
+               Option == LoopHintAttr::Distribute) {
       assert(StateLoc && StateLoc->Ident && "Loop hint must have an argument");
       if (StateLoc->Ident->isStr("disable"))
         State = LoopHintAttr::Disable;
@@ -140,18 +142,21 @@ static Attr *handleLoopHintAttr(Sema &S, Stmt *St, const AttributeList &A,
 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.
+  // There are 4 categories of loop hints attributes: vectorize, interleave,
+  // unroll and distribute. Except for distribute they come 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 *StateAttr;
     const LoopHintAttr *NumericAttr;
-  } HintAttrs[] = {{nullptr, nullptr}, {nullptr, nullptr}, {nullptr, nullptr}};
+  } HintAttrs[] = {{nullptr, nullptr},
+                   {nullptr, nullptr},
+                   {nullptr, nullptr},
+                   {nullptr, nullptr}};
 
   for (const auto *I : Attrs) {
     const LoopHintAttr *LH = dyn_cast<LoopHintAttr>(I);
@@ -161,7 +166,7 @@ CheckForIncompatibleAttributes(Sema &S,
       continue;
 
     LoopHintAttr::OptionType Option = LH->getOption();
-    enum { Vectorize, Interleave, Unroll } Category;
+    enum { Vectorize, Interleave, Unroll, Distribute } Category;
     switch (Option) {
     case LoopHintAttr::Vectorize:
     case LoopHintAttr::VectorizeWidth:
@@ -175,12 +180,17 @@ CheckForIncompatibleAttributes(Sema &S,
     case LoopHintAttr::UnrollCount:
       Category = Unroll;
       break;
+    case LoopHintAttr::Distribute:
+      // Perform the check for duplicated 'distribute' hints.
+      Category = Distribute;
+      break;
     };
 
     auto &CategoryState = HintAttrs[Category];
     const LoopHintAttr *PrevAttr;
     if (Option == LoopHintAttr::Vectorize ||
-        Option == LoopHintAttr::Interleave || Option == LoopHintAttr::Unroll) {
+        Option == LoopHintAttr::Interleave || Option == LoopHintAttr::Unroll ||
+        Option == LoopHintAttr::Distribute) {
       // Enable|Disable|AssumeSafety hint.  For example, vectorize(enable).
       PrevAttr = CategoryState.StateAttr;
       CategoryState.StateAttr = LH;
diff --git a/test/CodeGenCXX/pragma-loop.cpp b/test/CodeGenCXX/pragma-loop.cpp
index b85e0b49b9..e337913646 100644
--- a/test/CodeGenCXX/pragma-loop.cpp
+++ b/test/CodeGenCXX/pragma-loop.cpp
@@ -9,6 +9,7 @@ void while_test(int *List, int Length) {
 #pragma clang loop interleave_count(4)
 #pragma clang loop vectorize_width(4)
 #pragma clang loop unroll(full)
+#pragma clang loop distribute(enable)
   while (i < Length) {
     // CHECK: br label {{.*}}, !llvm.loop ![[LOOP_1:.*]]
     List[i] = i * 2;
@@ -20,7 +21,7 @@ void while_test(int *List, int Length) {
 void do_test(int *List, int Length) {
   int i = 0;
 
-#pragma clang loop vectorize_width(8) interleave_count(4) unroll(disable)
+#pragma clang loop vectorize_width(8) interleave_count(4) unroll(disable) distribute(disable)
   do {
     // CHECK: br i1 {{.*}}, label {{.*}}, label {{.*}}, !llvm.loop ![[LOOP_2:.*]]
     List[i] = i * 2;
@@ -55,7 +56,7 @@ void for_range_test() {
 
 // Verify disable pragma clang loop directive generates correct metadata
 void disable_test(int *List, int Length) {
-#pragma clang loop vectorize(disable) unroll(disable)
+#pragma clang loop vectorize(disable) unroll(disable) distribute(disable)
   for (int i = 0; i < Length; i++) {
     // CHECK: br label {{.*}}, !llvm.loop ![[LOOP_5:.*]]
     List[i] = i * 2;
@@ -157,20 +158,22 @@ void template_test(double *List, int Length) {
   for_template_constant_expression_test<double, 2, 4, 8>(List, Length);
 }
 
-// CHECK: ![[LOOP_1]] = distinct !{![[LOOP_1]], ![[WIDTH_4:.*]], ![[INTERLEAVE_4:.*]], ![[INTENABLE_1:.*]], ![[UNROLL_FULL:.*]]}
+// CHECK: ![[LOOP_1]] = distinct !{![[LOOP_1]], ![[WIDTH_4:.*]], ![[INTERLEAVE_4:.*]], ![[INTENABLE_1:.*]], ![[UNROLL_FULL:.*]], ![[DISTRIBUTE_ENABLE:.*]]}
 // CHECK: ![[WIDTH_4]] = !{!"llvm.loop.vectorize.width", i32 4}
 // CHECK: ![[INTERLEAVE_4]] = !{!"llvm.loop.interleave.count", i32 4}
 // CHECK: ![[INTENABLE_1]] = !{!"llvm.loop.vectorize.enable", i1 true}
 // CHECK: ![[UNROLL_FULL]] = !{!"llvm.loop.unroll.full"}
-// CHECK: ![[LOOP_2]] = distinct !{![[LOOP_2:.*]], ![[WIDTH_8:.*]], ![[INTERLEAVE_4:.*]], ![[UNROLL_DISABLE:.*]]}
+// CHECK: ![[DISTRIBUTE_ENABLE]] = !{!"llvm.loop.distribute.enable", i1 true}
+// CHECK: ![[LOOP_2]] = distinct !{![[LOOP_2:.*]], ![[WIDTH_8:.*]], ![[INTERLEAVE_4:.*]], ![[UNROLL_DISABLE:.*]], ![[DISTRIBUTE_DISABLE:.*]]}
 // CHECK: ![[WIDTH_8]] = !{!"llvm.loop.vectorize.width", i32 8}
 // CHECK: ![[UNROLL_DISABLE]] = !{!"llvm.loop.unroll.disable"}
+// CHECK: ![[DISTRIBUTE_DISABLE]] = !{!"llvm.loop.distribute.enable", i1 false}
 // CHECK: ![[LOOP_3]] = distinct !{![[LOOP_3]], ![[INTERLEAVE_4:.*]], ![[UNROLL_8:.*]], ![[INTENABLE_1:.*]]}
 // CHECK: ![[UNROLL_8]] = !{!"llvm.loop.unroll.count", i32 8}
 // CHECK: ![[LOOP_4]] = distinct !{![[LOOP_4]], ![[WIDTH_2:.*]], ![[INTERLEAVE_2:.*]]}
 // CHECK: ![[WIDTH_2]] = !{!"llvm.loop.vectorize.width", i32 2}
 // CHECK: ![[INTERLEAVE_2]] = !{!"llvm.loop.interleave.count", i32 2}
-// CHECK: ![[LOOP_5]] = distinct !{![[LOOP_5]], ![[WIDTH_1:.*]], ![[UNROLL_DISABLE:.*]]}
+// CHECK: ![[LOOP_5]] = distinct !{![[LOOP_5]], ![[WIDTH_1:.*]], ![[UNROLL_DISABLE:.*]], ![[DISTRIBUTE_DISABLE:.*]]}
 // CHECK: ![[WIDTH_1]] = !{!"llvm.loop.vectorize.width", i32 1}
 // CHECK: ![[LOOP_6]] = distinct !{![[LOOP_6]], ![[WIDTH_2:.*]], ![[INTERLEAVE_2:.*]], ![[UNROLL_8:.*]]}
 // CHECK: ![[LOOP_7]] = distinct !{![[LOOP_7]], ![[WIDTH_5:.*]]}
diff --git a/test/Misc/ast-print-pragmas.cpp b/test/Misc/ast-print-pragmas.cpp
index c4fe1e23b1..5840c1a2c3 100644
--- a/test/Misc/ast-print-pragmas.cpp
+++ b/test/Misc/ast-print-pragmas.cpp
@@ -19,7 +19,9 @@ void test(int *List, int Length) {
 
 // CHECK: #pragma clang loop interleave(disable)
 // CHECK-NEXT: #pragma clang loop vectorize(enable)
+// CHECK-NEXT: #pragma clang loop distribute(disable)
 
+#pragma clang loop distribute(disable)
 #pragma clang loop vectorize(enable)
 #pragma clang loop interleave(disable)
 // CHECK-NEXT: while (i - 1 < Length)
@@ -30,7 +32,9 @@ void test(int *List, int Length) {
 
 // CHECK: #pragma clang loop interleave(enable)
 // CHECK-NEXT: #pragma clang loop vectorize(disable)
+// CHECK-NEXT: #pragma clang loop distribute(enable)
 
+#pragma clang loop distribute(enable)
 #pragma clang loop vectorize(disable)
 #pragma clang loop interleave(enable)
 // CHECK-NEXT: while (i - 2 < Length)
diff --git a/test/PCH/pragma-loop.cpp b/test/PCH/pragma-loop.cpp
index 2640020f00..5975816f69 100644
--- a/test/PCH/pragma-loop.cpp
+++ b/test/PCH/pragma-loop.cpp
@@ -7,9 +7,11 @@
 // CHECK: #pragma clang loop unroll_count(16)
 // CHECK: #pragma clang loop interleave_count(8)
 // CHECK: #pragma clang loop vectorize_width(4)
+// CHECK: #pragma clang loop distribute(enable)
 // CHECK: #pragma clang loop unroll(disable)
 // CHECK: #pragma clang loop interleave(disable)
 // CHECK: #pragma clang loop vectorize(enable)
+// CHECK: #pragma clang loop distribute(disable)
 // CHECK: #pragma clang loop unroll(full)
 // CHECK: #pragma clang loop interleave(enable)
 // CHECK: #pragma clang loop vectorize(disable)
@@ -40,6 +42,7 @@ public:
 #pragma clang loop vectorize(enable)
 #pragma clang loop interleave(disable)
 #pragma clang loop unroll(disable)
+#pragma clang loop distribute(enable)
     while (i - 1 < Length) {
       List[i] = i;
       i++;
@@ -51,6 +54,7 @@ public:
 #pragma clang loop vectorize(disable)
 #pragma clang loop interleave(enable)
 #pragma clang loop unroll(full)
+#pragma clang loop distribute(disable)
     while (i - 3 < Length) {
       List[i] = i;
       i++;
diff --git a/test/Parser/pragma-loop-safety.cpp b/test/Parser/pragma-loop-safety.cpp
index 0776000e51..ab87dcdcb6 100644
--- a/test/Parser/pragma-loop-safety.cpp
+++ b/test/Parser/pragma-loop-safety.cpp
@@ -16,6 +16,7 @@ void test(int *List, int Length) {
 /* expected-error {{expected ')'}} */ #pragma clang loop interleave(assume_safety
 
 /* expected-error {{invalid argument; expected 'enable', 'full' or 'disable'}} */ #pragma clang loop unroll(assume_safety)
+/* expected-error {{invalid argument; expected 'enable' or 'disable'}} */ #pragma clang loop distribute(assume_safety)
 
 /* expected-error {{invalid argument; expected 'enable', 'assume_safety' or 'disable'}} */ #pragma clang loop vectorize(badidentifier)
 /* expected-error {{invalid argument; expected 'enable', 'assume_safety' or 'disable'}} */ #pragma clang loop interleave(badidentifier)
diff --git a/test/Parser/pragma-loop.cpp b/test/Parser/pragma-loop.cpp
index b9b5b41efb..f42d196ce8 100644
--- a/test/Parser/pragma-loop.cpp
+++ b/test/Parser/pragma-loop.cpp
@@ -116,15 +116,27 @@ void test(int *List, int Length) {
     VList[j] = List[j];
   }
 
+#pragma clang loop distribute(enable)
+  for (int j : VList) {
+    VList[j] = List[j];
+  }
+
+#pragma clang loop distribute(disable)
+  for (int j : VList) {
+    VList[j] = List[j];
+  }
+
   test_nontype_template_param<4, 8>(List, Length);
 
 /* expected-error {{expected '('}} */ #pragma clang loop vectorize
 /* expected-error {{expected '('}} */ #pragma clang loop interleave
 /* expected-error {{expected '('}} */ #pragma clang loop unroll
+/* expected-error {{expected '('}} */ #pragma clang loop distribute
 
 /* expected-error {{expected ')'}} */ #pragma clang loop vectorize(enable
 /* expected-error {{expected ')'}} */ #pragma clang loop interleave(enable
 /* expected-error {{expected ')'}} */ #pragma clang loop unroll(full
+/* expected-error {{expected ')'}} */ #pragma clang loop distribute(enable
 
 /* expected-error {{expected ')'}} */ #pragma clang loop vectorize_width(4
 /* expected-error {{expected ')'}} */ #pragma clang loop interleave_count(4
@@ -133,8 +145,9 @@ void test(int *List, int Length) {
 /* expected-error {{missing argument; expected 'enable', 'assume_safety' or 'disable'}} */ #pragma clang loop vectorize()
 /* expected-error {{missing argument; expected an integer value}} */ #pragma clang loop interleave_count()
 /* expected-error {{missing argument; expected 'enable', 'full' or 'disable'}} */ #pragma clang loop unroll()
+/* expected-error {{missing argument; expected 'enable' or 'disable'}} */ #pragma clang loop distribute()
 
-/* expected-error {{missing option; expected vectorize, vectorize_width, interleave, interleave_count, unroll, or unroll_count}} */ #pragma clang loop
+/* expected-error {{missing option; expected vectorize, vectorize_width, interleave, interleave_count, unroll, unroll_count, or distribute}} */ #pragma clang loop
 /* expected-error {{invalid option 'badkeyword'}} */ #pragma clang loop badkeyword
 /* expected-error {{invalid option 'badkeyword'}} */ #pragma clang loop badkeyword(enable)
 /* expected-error {{invalid option 'badkeyword'}} */ #pragma clang loop vectorize(enable) badkeyword(4)
@@ -187,6 +200,7 @@ const int VV = 4;
 /* expected-error {{invalid argument; expected 'enable', 'assume_safety' or 'disable'}} */ #pragma clang loop vectorize(badidentifier)
 /* expected-error {{invalid argument; expected 'enable', 'assume_safety' or 'disable'}} */ #pragma clang loop interleave(badidentifier)
 /* expected-error {{invalid argument; expected 'enable', 'full' or 'disable'}} */ #pragma clang loop unroll(badidentifier)
+/* expected-error {{invalid argument; expected 'enable' or 'disable'}} */ #pragma clang loop distribute(badidentifier)
   while (i-7 < Length) {
     List[i] = i;
   }
@@ -196,6 +210,7 @@ const int VV = 4;
 /* expected-error {{expected ')'}} */ #pragma clang loop vectorize(()
 /* expected-error {{invalid argument; expected 'enable', 'assume_safety' or 'disable'}} */ #pragma clang loop interleave(*)
 /* expected-error {{invalid argument; expected 'enable', 'full' or 'disable'}} */ #pragma clang loop unroll(=)
+/* expected-error {{invalid argument; expected 'enable' or 'disable'}} */ #pragma clang loop distribute(+)
 /* expected-error {{type name requires a specifier or qualifier}} expected-error {{expected expression}} */ #pragma clang loop vectorize_width(^)
 /* expected-error {{expected expression}} expected-error {{expected expression}} */ #pragma clang loop interleave_count(/)
 /* expected-error {{expected expression}} expected-error {{expected expression}} */ #pragma clang loop unroll_count(==)
@@ -232,6 +247,8 @@ const int VV = 4;
 #pragma clang loop interleave(disable)
 /* expected-error {{duplicate directives 'unroll(disable)' and 'unroll(full)'}} */ #pragma clang loop unroll(full)
 #pragma clang loop unroll(disable)
+/* expected-error {{duplicate directives 'distribute(disable)' and 'distribute(enable)'}} */ #pragma clang loop distribute(enable)
+#pragma clang loop distribute(disable)
   while (i-9 < Length) {
     List[i] = i;
   }