Add #pragma clang loop ivdep

[YashasAndaluri]

Summary

This patch adds a ivdep pragma to indicate to the vectorizer using the llvm.loop.vectorize.ivdep.enable metadata that dependencies of Unknown type can be considered to be safe for vectorization. This pragma will also imply vectorize(enable). This patch is used by D70634
Usage:

#pragma clang loop ivdep(enable)

[YashasAndaluri]

Updated the diff to show context

[xbolva00]

"#pragma ivdep" should work too (compatibiluty mode with intel, gcc).

[hfinkel]

This is the same as #pragma clang loop vectorize(assume_safety)?

In D69391#1720845, @xbolva00 wrote:

"#pragma ivdep" should work too (compatibiluty mode with intel, gcc).

The semantics are not the same, unfortunately.

[YashasAndaluri]

Removed disable argument for ivdep

[YashasAndaluri]

Added IvdepEnable loop attribute and llvm.loop.vectorize.ivdep.enable metadata.

clang/docs/LanguageExtensions.rst

 these two instantiations, ``twice`` will be optimized (because its definition
 was outside the region) and ``thrice`` will not be optimized.
 
 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, predication, unrolling and
-distribution. 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, predication, ignoring vector
+dependencies, unrolling and distribution. Loop hints can be specified before any
+loop and will be ignored if the optimization is not safe to apply.
 
 There are loop hints that control transformations (e.g. vectorization, loop
 unrolling) and there are loop hints that set transformation options (e.g.
 ``vectorize_width``, ``unroll_count``).  Pragmas setting transformation options
 imply the transformation is enabled, as if it was enabled via the corresponding
 transformation pragma (e.g. ``vectorize(enable)``). If the transformation is
 disabled  (e.g. ``vectorize(disable)``), that takes precedence over
 transformations option pragmas implying that transformation.
for(...) {
     ...
   }
 
 This predicates (masks) all instructions in the loop, which allows the scalar
 remainder loop (the tail) to be folded into the main vectorized loop. This
 might be more efficient when vector predication is efficiently supported by the
 target platform.
 
+Ignore Vector Dependencies in loop
+----------------------------------
+Dependencies in a loop of unknown dependence type that inhibit vectorization of
+the loop can be ignored by using ``ivdep(enable)``.
+
+.. code-block:: c++
+
+  #pragma clang loop ivdep(enable)
+  for(...) {
+    ...
+  }
+
+This hints to the vectorizer that dependencies that have not been determined to
+be safe or unsafe for vectorization will be ignored. This pragma will also imply
+``vectorize(enable)``.
+
 Loop Unrolling
 --------------
 
 Unrolling a loop reduces the loop control overhead and exposes more
 opportunities for ILP. Loops can be fully or partially unrolled. Full unrolling
 eliminates the loop and replaces it with an enumerated sequence of loop
 iterations. Full unrolling is only possible if the loop trip count is known at
 compile time. Partial unrolling replicates the loop body within the loop and

clang/include/clang/Basic/Attr.td

let Spellings = [Pragma<"clang", "loop">, Pragma<"", "unroll">,
                    Pragma<"", "nounroll">, Pragma<"", "unroll_and_jam">,
                    Pragma<"", "nounroll_and_jam">];
 
   /// State of the loop optimization specified by the spelling.
   let Args = [EnumArgument<"Option", "OptionType",
                           ["vectorize", "vectorize_width", "interleave", "interleave_count",
                            "unroll", "unroll_count", "unroll_and_jam", "unroll_and_jam_count",
                            "pipeline", "pipeline_initiation_interval", "distribute",
-                           "vectorize_predicate"],
+                           "vectorize_predicate", "ivdep"],
                           ["Vectorize", "VectorizeWidth", "Interleave", "InterleaveCount",
                            "Unroll", "UnrollCount", "UnrollAndJam", "UnrollAndJamCount",
                            "PipelineDisabled", "PipelineInitiationInterval", "Distribute",
-                           "VectorizePredicate"]>,
+                           "VectorizePredicate", "Ivdep"]>,
               EnumArgument<"State", "LoopHintState",
                            ["enable", "disable", "numeric", "assume_safety", "full"],
                            ["Enable", "Disable", "Numeric", "AssumeSafety", "Full"]>,
               ExprArgument<"Value">];
 
   let AdditionalMembers = [{
   static const char *getOptionName(int Option) {
     switch(Option) {
     case Vectorize: return "vectorize";
     case VectorizeWidth: return "vectorize_width";
     case Interleave: return "interleave";
     case InterleaveCount: return "interleave_count";
     case Unroll: return "unroll";
     case UnrollCount: return "unroll_count";
     case UnrollAndJam: return "unroll_and_jam";
     case UnrollAndJamCount: return "unroll_and_jam_count";
     case PipelineDisabled: return "pipeline";
     case PipelineInitiationInterval: return "pipeline_initiation_interval";
     case Distribute: return "distribute";
     case VectorizePredicate: return "vectorize_predicate";
+    case Ivdep: return "ivdep";
     }
     llvm_unreachable("Unhandled LoopHint option.");
   }
 
   void printPrettyPragma(raw_ostream &OS, const PrintingPolicy &Policy) const {
     unsigned SpellingIndex = getAttributeSpellingListIndex();
     // For "#pragma unroll" and "#pragma nounroll" the string "unroll" or
     // "nounroll" is already emitted as the pragma name.

clang/include/clang/Basic/AttrDocs.td

 }
 
 def LoopHintDocs : Documentation {
   let Category = DocCatStmt;
   let Heading = "#pragma clang loop";
   let Content = [{
 The ``#pragma clang loop`` directive allows loop optimization hints to be
 specified for the subsequent loop. The directive allows pipelining to be
-disabled, or vectorization, vector predication, interleaving, and unrolling to
-be enabled or disabled. Vector width, vector predication, interleave count,
-unrolling count, and the initiation interval for pipelining can be explicitly
-specified. See `language extensions
+disabled, vector dependencies to be ignored, or vectorization, vector
+predication, interleaving, and unrolling to be enabled or disabled. Vector
+width, vector predication, interleave count, unrolling count, and the
+initiation interval for pipelining can be explicitly specified.
+See `language extensions
 <http://clang.llvm.org/docs/LanguageExtensions.html#extensions-for-loop-hint-optimizations>`_
 for details.
   }];
 }
 
 def UnrollHintDocs : Documentation {
   let Category = DocCatStmt;
   let Heading = "#pragma unroll, #pragma nounroll";

clang/include/clang/Basic/DiagnosticParseKinds.td

 
 // Pragma loop support.
 def err_pragma_loop_missing_argument : Error<
   "missing argument; expected %select{an integer value|"
   "'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, unroll_count, "
-  "pipeline, pipeline_initiation_interval, vectorize_predicate, or distribute">;
+  "pipeline, pipeline_initiation_interval, vectorize_predicate, ivdep, or distribute">;
 
 def err_pragma_fp_invalid_option : Error<
   "%select{invalid|missing}0 option%select{ %1|}0; expected contract">;
 def err_pragma_fp_invalid_argument : Error<
   "unexpected argument '%0' to '#pragma clang fp %1'; "
   "expected 'on', 'fast' or 'off'">;
 def err_pragma_fp_scope : Error<
   "'#pragma clang fp' can only appear at file scope or at the start of a "
   "compound statement">;
 
 def err_pragma_invalid_keyword : Error<
   "invalid argument; expected 'enable'%select{|, 'full'}0%select{|, 'assume_safety'}1 or 'disable'">;
 def err_pragma_pipeline_invalid_keyword : Error<
     "invalid argument; expected 'disable'">;
+def err_pragma_ivdep_invalid_keyword : Error<
+    "invalid argument; expected 'enable'">;
 
 // Pragma unroll support.
 def warn_pragma_unroll_cuda_value_in_parens : Warning<
   "argument to '#pragma unroll' should not be in parentheses in CUDA C/C++">,
   InGroup<CudaCompat>;
 
 def warn_cuda_attr_lambda_position : Warning<
   "nvcc does not allow '__%0__' to appear after '()' in lambdas">,

clang/lib/CodeGen/CGLoopInfo.h

struct LoopAttributes {
   LVEnableState UnrollEnable;
 
   /// Value for llvm.loop.unroll_and_jam.* metadata (enable, disable, or full).
   LVEnableState UnrollAndJamEnable;
 
   /// Value for llvm.loop.vectorize.predicate metadata
   LVEnableState VectorizePredicateEnable;
 
+  /// Value for llvm.loop.vectorize.ivdep.enable metadata.
+  bool IvdepEnable;
+
   /// Value for llvm.loop.vectorize.width metadata.
   unsigned VectorizeWidth;
 
   /// Value for llvm.loop.interleave.count metadata.
   unsigned InterleaveCount;
 
   /// llvm.unroll.
   unsigned UnrollCount;
void setVectorizePredicateState(const LoopAttributes::LVEnableState &State) {
     StagedAttrs.VectorizePredicateEnable = State;
   }
 
   /// Set the next pushed loop unroll_and_jam state.
   void setUnrollAndJamState(const LoopAttributes::LVEnableState &State) {
     StagedAttrs.UnrollAndJamEnable = State;
   }
 
+  /// Set the next pushed loop ivdep enable state.
+  void setIvdepEnable(bool S) { StagedAttrs.IvdepEnable = S; }
+
   /// Set the vectorize width for the next loop pushed.
   void setVectorizeWidth(unsigned W) { StagedAttrs.VectorizeWidth = W; }
 
   /// Set the interleave count for the next loop pushed.
   void setInterleaveCount(unsigned C) { StagedAttrs.InterleaveCount = C; }
 
   /// Set the unroll count for the next loop pushed.
   void setUnrollCount(unsigned C) { StagedAttrs.UnrollCount = C; }

clang/lib/CodeGen/CGLoopInfo.cpp

if (Attrs.VectorizePredicateEnable != LoopAttributes::Unspecified &&
 
     Metadata *Vals[] = {
         MDString::get(Ctx, "llvm.loop.vectorize.predicate.enable"),
         ConstantAsMetadata::get(ConstantInt::get(llvm::Type::getInt1Ty(Ctx),
                                                  IsVectorPredicateEnabled))};
     Args.push_back(MDNode::get(Ctx, Vals));
   }
 
+  // Setting vectorize.ivdep.enable
+  if (Attrs.IvdepEnable == true &&
+      Attrs.VectorizeEnable != LoopAttributes::Disable) {
+    Metadata *Vals[] = {
+        MDString::get(Ctx,"llvm.loop.vectorize.ivdep.enable"),
+        ConstantAsMetadata::get(ConstantInt::get(llvm::Type::getInt1Ty(Ctx),
+                                                 true))};
+    Args.push_back(MDNode::get(Ctx,Vals));
+  }
+
   // Setting vectorize.width
   if (Attrs.VectorizeWidth > 0) {
     // This implies vectorize.enable = true, but only add it when it is not
     // already enabled.
     if (Attrs.VectorizeEnable != LoopAttributes::Enable)
       Args.push_back(
           MDNode::get(Ctx, {MDString::get(Ctx, "llvm.loop.vectorize.enable"),
                             ConstantAsMetadata::get(ConstantInt::get(
LoopProperties.insert(LoopProperties.end(), AdditionalLoopProperties.begin(),
                         AdditionalLoopProperties.end());
   return createFullUnrollMetadata(Attrs, LoopProperties, HasUserTransforms);
 }
 
 LoopAttributes::LoopAttributes(bool IsParallel)
     : IsParallel(IsParallel), VectorizeEnable(LoopAttributes::Unspecified),
       UnrollEnable(LoopAttributes::Unspecified),
       UnrollAndJamEnable(LoopAttributes::Unspecified),
-      VectorizePredicateEnable(LoopAttributes::Unspecified), VectorizeWidth(0),
-      InterleaveCount(0), UnrollCount(0), UnrollAndJamCount(0),
+      VectorizePredicateEnable(LoopAttributes::Unspecified),
+      IvdepEnable(false), VectorizeWidth(0), InterleaveCount(0),
+      UnrollCount(0), UnrollAndJamCount(0),
       DistributeEnable(LoopAttributes::Unspecified), PipelineDisabled(false),
       PipelineInitiationInterval(0) {}
 
 void LoopAttributes::clear() {
   IsParallel = false;
   VectorizeWidth = 0;
   InterleaveCount = 0;
   UnrollCount = 0;
   UnrollAndJamCount = 0;
   VectorizeEnable = LoopAttributes::Unspecified;
   UnrollEnable = LoopAttributes::Unspecified;
   UnrollAndJamEnable = LoopAttributes::Unspecified;
   VectorizePredicateEnable = LoopAttributes::Unspecified;
+  IvdepEnable = false;
   DistributeEnable = LoopAttributes::Unspecified;
   PipelineDisabled = false;
   PipelineInitiationInterval = 0;
 }
 
 LoopInfo::LoopInfo(BasicBlock *Header, const LoopAttributes &Attrs,
                    const llvm::DebugLoc &StartLoc, const llvm::DebugLoc &EndLoc,
                    LoopInfo *Parent)
     : Header(Header), Attrs(Attrs), StartLoc(StartLoc), EndLoc(EndLoc),
       Parent(Parent) {
 
   if (Attrs.IsParallel) {
     // Create an access group for this loop.
     LLVMContext &Ctx = Header->getContext();
     AccGroup = MDNode::getDistinct(Ctx, {});
   }
 
   if (!Attrs.IsParallel && Attrs.VectorizeWidth == 0 &&
       Attrs.InterleaveCount == 0 && Attrs.UnrollCount == 0 &&
       Attrs.UnrollAndJamCount == 0 && !Attrs.PipelineDisabled &&
-      Attrs.PipelineInitiationInterval == 0 &&
+      Attrs.PipelineInitiationInterval == 0 && !Attrs.IvdepEnable &&
       Attrs.VectorizePredicateEnable == LoopAttributes::Unspecified &&
       Attrs.VectorizeEnable == LoopAttributes::Unspecified &&
       Attrs.UnrollEnable == LoopAttributes::Unspecified &&
       Attrs.UnrollAndJamEnable == LoopAttributes::Unspecified &&
       Attrs.DistributeEnable == LoopAttributes::Unspecified && !StartLoc &&
       !EndLoc)
     return;
 
if (Parent && (Parent->Attrs.UnrollAndJamEnable ||
 
     BeforeJam.IsParallel = AfterJam.IsParallel = Attrs.IsParallel;
 
     BeforeJam.VectorizeWidth = Attrs.VectorizeWidth;
     BeforeJam.InterleaveCount = Attrs.InterleaveCount;
     BeforeJam.VectorizeEnable = Attrs.VectorizeEnable;
     BeforeJam.DistributeEnable = Attrs.DistributeEnable;
     BeforeJam.VectorizePredicateEnable = Attrs.VectorizePredicateEnable;
+    BeforeJam.IvdepEnable = Attrs.IvdepEnable;
 
     switch (Attrs.UnrollEnable) {
     case LoopAttributes::Unspecified:
     case LoopAttributes::Disable:
       BeforeJam.UnrollEnable = Attrs.UnrollEnable;
       AfterJam.UnrollEnable = Attrs.UnrollEnable;
       break;
     case LoopAttributes::Full:
       BeforeJam.UnrollEnable = LoopAttributes::Full;
       break;
     case LoopAttributes::Enable:
       AfterJam.UnrollEnable = LoopAttributes::Enable;
       break;
     }
 
     AfterJam.VectorizePredicateEnable = Attrs.VectorizePredicateEnable;
+    AfterJam.IvdepEnable = Attrs.IvdepEnable;
     AfterJam.UnrollCount = Attrs.UnrollCount;
     AfterJam.PipelineDisabled = Attrs.PipelineDisabled;
     AfterJam.PipelineInitiationInterval = Attrs.PipelineInitiationInterval;
 
     // If this loop is subject of an unroll-and-jam by the parent loop, and has
     // an unroll-and-jam annotation itself, we have to decide whether to first
     // apply the parent's unroll-and-jam or this loop's unroll-and-jam. The
     // UnrollAndJam pass processes loops from inner to outer, so we apply the
case LoopHintAttr::Disable:
         setVectorizePredicateState(LoopAttributes::Disable);
         break;
       case LoopHintAttr::Distribute:
         setDistributeState(false);
         break;
       case LoopHintAttr::PipelineDisabled:
         setPipelineDisabled(true);
         break;
+      case LoopHintAttr::Ivdep:
       case LoopHintAttr::UnrollCount:
       case LoopHintAttr::UnrollAndJamCount:
       case LoopHintAttr::VectorizeWidth:
       case LoopHintAttr::InterleaveCount:
       case LoopHintAttr::PipelineInitiationInterval:
         llvm_unreachable("Options cannot be disabled.");
         break;
       }
case LoopHintAttr::Enable:
         setUnrollAndJamState(LoopAttributes::Enable);
         break;
       case LoopHintAttr::VectorizePredicate:
         setVectorizePredicateState(LoopAttributes::Enable);
         break;
       case LoopHintAttr::Distribute:
         setDistributeState(true);
         break;
+      case LoopHintAttr::Ivdep:
+        setIvdepEnable(true);
+        setVectorizeEnable(true);
+        break;
       case LoopHintAttr::UnrollCount:
       case LoopHintAttr::UnrollAndJamCount:
       case LoopHintAttr::VectorizeWidth:
       case LoopHintAttr::InterleaveCount:
       case LoopHintAttr::PipelineDisabled:
       case LoopHintAttr::PipelineInitiationInterval:
         llvm_unreachable("Options cannot enabled.");
         break;
       }
       break;
     case LoopHintAttr::AssumeSafety:
       switch (Option) {
       case LoopHintAttr::Vectorize:
       case LoopHintAttr::Interleave:
         // Apply "llvm.mem.parallel_loop_access" metadata to load/stores.
         setParallel(true);
         setVectorizeEnable(true);
         break;
       case LoopHintAttr::Unroll:
       case LoopHintAttr::UnrollAndJam:
       case LoopHintAttr::VectorizePredicate:
+      case LoopHintAttr::Ivdep:
       case LoopHintAttr::UnrollCount:
       case LoopHintAttr::UnrollAndJamCount:
       case LoopHintAttr::VectorizeWidth:
       case LoopHintAttr::InterleaveCount:
       case LoopHintAttr::Distribute:
       case LoopHintAttr::PipelineDisabled:
       case LoopHintAttr::PipelineInitiationInterval:
         llvm_unreachable("Options cannot be used to assume mem safety.");
         break;
       }
       break;
     case LoopHintAttr::Full:
       switch (Option) {
       case LoopHintAttr::Unroll:
         setUnrollState(LoopAttributes::Full);
         break;
       case LoopHintAttr::UnrollAndJam:
         setUnrollAndJamState(LoopAttributes::Full);
         break;
       case LoopHintAttr::Vectorize:
       case LoopHintAttr::Interleave:
+      case LoopHintAttr::Ivdep:
       case LoopHintAttr::UnrollCount:
       case LoopHintAttr::UnrollAndJamCount:
       case LoopHintAttr::VectorizeWidth:
       case LoopHintAttr::InterleaveCount:
       case LoopHintAttr::Distribute:
       case LoopHintAttr::PipelineDisabled:
       case LoopHintAttr::PipelineInitiationInterval:
       case LoopHintAttr::VectorizePredicate:
case LoopHintAttr::Numeric:
         break;
       case LoopHintAttr::PipelineInitiationInterval:
         setPipelineInitiationInterval(ValueInt);
         break;
       case LoopHintAttr::Unroll:
       case LoopHintAttr::UnrollAndJam:
       case LoopHintAttr::VectorizePredicate:
       case LoopHintAttr::Vectorize:
+      case LoopHintAttr::Ivdep:
       case LoopHintAttr::Interleave:
       case LoopHintAttr::Distribute:
       case LoopHintAttr::PipelineDisabled:
         llvm_unreachable("Options cannot be assigned a value.");
         break;
       }
       break;
     }

clang/lib/Parse/ParsePragma.cpp

bool Parser::HandlePragmaLoopHint(LoopHint &Hint) {
   assert(!Toks.empty() &&
          "PragmaLoopHintInfo::Toks must contain at least one token.");
 
   // If no option is specified the argument is assumed to be a constant expr.
   bool OptionUnroll = false;
   bool OptionUnrollAndJam = false;
   bool OptionDistribute = false;
   bool OptionPipelineDisabled = false;
+  bool OptionIvdepEnabled = false;
   bool StateOption = false;
   if (OptionInfo) { // Pragma Unroll does not specify an option.
     OptionUnroll = OptionInfo->isStr("unroll");
     OptionUnrollAndJam = OptionInfo->isStr("unroll_and_jam");
     OptionDistribute = OptionInfo->isStr("distribute");
     OptionPipelineDisabled = OptionInfo->isStr("pipeline");
+    OptionIvdepEnabled = OptionInfo->isStr("ivdep");
     StateOption = llvm::StringSwitch<bool>(OptionInfo->getName())
                       .Case("vectorize", true)
                       .Case("interleave", true)
                       .Case("vectorize_predicate", true)
                       .Default(false) ||
                   OptionUnroll || OptionUnrollAndJam || OptionDistribute ||
-                  OptionPipelineDisabled;
+                  OptionPipelineDisabled || OptionIvdepEnabled;
   }
 
   bool AssumeSafetyArg = !OptionUnroll && !OptionUnrollAndJam &&
-                         !OptionDistribute && !OptionPipelineDisabled;
+                         !OptionDistribute && !OptionPipelineDisabled &&
+                         !OptionIvdepEnabled;
   // Verify loop hint has an argument.
   if (Toks[0].is(tok::eof)) {
     ConsumeAnnotationToken();
     Diag(Toks[0].getLocation(), diag::err_pragma_loop_missing_argument)
         << /*StateArgument=*/StateOption
         << /*FullKeyword=*/(OptionUnroll || OptionUnrollAndJam)
         << /*AssumeSafetyKeyword=*/AssumeSafetyArg;
     return false;
   }
 
   // Validate the argument.
   if (StateOption) {
     ConsumeAnnotationToken();
     SourceLocation StateLoc = Toks[0].getLocation();
     IdentifierInfo *StateInfo = Toks[0].getIdentifierInfo();
 
     bool Valid = StateInfo &&
                  llvm::StringSwitch<bool>(StateInfo->getName())
-                     .Case("disable", true)
+                     .Case("disable", !OptionIvdepEnabled)
                      .Case("enable", !OptionPipelineDisabled)
                      .Case("full", OptionUnroll || OptionUnrollAndJam)
                      .Case("assume_safety", AssumeSafetyArg)
                      .Default(false);
     if (!Valid) {
       if (OptionPipelineDisabled) {
         Diag(Toks[0].getLocation(), diag::err_pragma_pipeline_invalid_keyword);
+      } else if (OptionIvdepEnabled) {
+        Diag(Toks[0].getLocation(), diag::err_pragma_ivdep_invalid_keyword);
       } else {
         Diag(Toks[0].getLocation(), diag::err_pragma_invalid_keyword)
             << /*FullKeyword=*/(OptionUnroll || OptionUnrollAndJam)
             << /*AssumeSafetyKeyword=*/AssumeSafetyArg;
       }
       return false;
     }
     if (Toks.size() > 2)

 ///  loop-hints:
 ///    loop-hint loop-hints[opt]
 ///
 ///  loop-hint:
 ///    'vectorize' '(' loop-hint-keyword ')'
 ///    'interleave' '(' loop-hint-keyword ')'
 ///    'unroll' '(' unroll-hint-keyword ')'
 ///    'vectorize_predicate' '(' loop-hint-keyword ')'
+///    'ivdep' '(' enable ')'
 ///    'vectorize_width' '(' loop-hint-value ')'
 ///    'interleave_count' '(' loop-hint-value ')'
 ///    'unroll_count' '(' loop-hint-value ')'
 ///    'pipeline' '(' disable ')'
 ///    'pipeline_initiation_interval' '(' loop-hint-value ')'
 ///
 ///  loop-hint-keyword:
 ///    'enable'
while (Tok.is(tok::identifier)) {
     IdentifierInfo *OptionInfo = Tok.getIdentifierInfo();
 
     bool OptionValid = llvm::StringSwitch<bool>(OptionInfo->getName())
                            .Case("vectorize", true)
                            .Case("interleave", true)
                            .Case("unroll", true)
                            .Case("distribute", true)
                            .Case("vectorize_predicate", true)
+                           .Case("ivdep", true)
                            .Case("vectorize_width", true)
                            .Case("interleave_count", true)
                            .Case("unroll_count", true)
                            .Case("pipeline", true)
                            .Case("pipeline_initiation_interval", true)
                            .Default(false);
     if (!OptionValid) {
       PP.Diag(Tok.getLocation(), diag::err_pragma_loop_invalid_option)

clang/lib/Sema/SemaStmtAttr.cpp

if (PragmaName == "nounroll") {
     assert(OptionLoc && OptionLoc->Ident &&
            "Attribute must have valid option info.");
     Option = llvm::StringSwitch<LoopHintAttr::OptionType>(
                  OptionLoc->Ident->getName())
                  .Case("vectorize", LoopHintAttr::Vectorize)
                  .Case("vectorize_width", LoopHintAttr::VectorizeWidth)
                  .Case("interleave", LoopHintAttr::Interleave)
                  .Case("vectorize_predicate", LoopHintAttr::VectorizePredicate)
+                 .Case("ivdep", LoopHintAttr::Ivdep)
                  .Case("interleave_count", LoopHintAttr::InterleaveCount)
                  .Case("unroll", LoopHintAttr::Unroll)
                  .Case("unroll_count", LoopHintAttr::UnrollCount)
                  .Case("pipeline", LoopHintAttr::PipelineDisabled)
                  .Case("pipeline_initiation_interval",
                        LoopHintAttr::PipelineInitiationInterval)
                  .Case("distribute", LoopHintAttr::Distribute)
                  .Default(LoopHintAttr::Vectorize);
     if (Option == LoopHintAttr::VectorizeWidth ||
         Option == LoopHintAttr::InterleaveCount ||
         Option == LoopHintAttr::UnrollCount ||
         Option == LoopHintAttr::PipelineInitiationInterval) {
       assert(ValueExpr && "Attribute must have a valid value expression.");
       if (S.CheckLoopHintExpr(ValueExpr, St->getBeginLoc()))
         return nullptr;
       State = LoopHintAttr::Numeric;
     } else if (Option == LoopHintAttr::Vectorize ||
                Option == LoopHintAttr::Interleave ||
                Option == LoopHintAttr::VectorizePredicate ||
+               Option == LoopHintAttr::Ivdep ||
                Option == LoopHintAttr::Unroll ||
                Option == LoopHintAttr::Distribute ||
                Option == LoopHintAttr::PipelineDisabled) {
       assert(StateLoc && StateLoc->Ident && "Loop hint must have an argument");
       if (StateLoc->Ident->isStr("disable"))
         State = LoopHintAttr::Disable;
       else if (StateLoc->Ident->isStr("assume_safety"))
         State = LoopHintAttr::AssumeSafety;
CheckForIncompatibleAttributes(Sema &S,
   // 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},
                    {nullptr, nullptr}, {nullptr, nullptr}, {nullptr, nullptr},
-                   {nullptr, nullptr}};
+                   {nullptr, nullptr}, {nullptr, nullptr}};
 
   for (const auto *I : Attrs) {
     const LoopHintAttr *LH = dyn_cast<LoopHintAttr>(I);
 
     // Skip non loop hint attributes
     if (!LH)
       continue;
 
     LoopHintAttr::OptionType Option = LH->getOption();
     enum {
       Vectorize,
       Interleave,
+      Ivdep,
       Unroll,
       UnrollAndJam,
       Distribute,
       Pipeline,
       VectorizePredicate
     } Category;
     switch (Option) {
     case LoopHintAttr::Vectorize:
case LoopHintAttr::Distribute:
       break;
     case LoopHintAttr::PipelineDisabled:
     case LoopHintAttr::PipelineInitiationInterval:
       Category = Pipeline;
       break;
     case LoopHintAttr::VectorizePredicate:
       Category = VectorizePredicate;
       break;
+    case LoopHintAttr::Ivdep:
+      Category = Ivdep;
+      break;
     };
 
     assert(Category < sizeof(HintAttrs) / sizeof(HintAttrs[0]));
     auto &CategoryState = HintAttrs[Category];
     const LoopHintAttr *PrevAttr;
     if (Option == LoopHintAttr::Vectorize ||
-        Option == LoopHintAttr::Interleave || Option == LoopHintAttr::Unroll ||
+        Option == LoopHintAttr::Interleave ||
+        Option == LoopHintAttr::Ivdep ||
+        Option == LoopHintAttr::Unroll ||
         Option == LoopHintAttr::UnrollAndJam ||
         Option == LoopHintAttr::VectorizePredicate ||
         Option == LoopHintAttr::PipelineDisabled ||
         Option == LoopHintAttr::Distribute) {
       // Enable|Disable|AssumeSafety hint.  For example, vectorize(enable).
       PrevAttr = CategoryState.StateAttr;
       CategoryState.StateAttr = LH;
     } else {

clang/test/AST/ast-print-pragmas.cpp

while (i - 1 < Length) {
     List[i] = i * 2;
     i++;
   }
 
 // CHECK: #pragma clang loop distribute(enable)
 // CHECK-NEXT: #pragma clang loop vectorize(disable)
 // CHECK-NEXT: #pragma clang loop interleave(enable)
 // CHECK-NEXT: #pragma clang loop vectorize_predicate(enable)
+// CHECK-NEXT: #pragma clang loop ivdep(enable)
 
 #pragma clang loop distribute(enable)
 #pragma clang loop vectorize(disable)
 #pragma clang loop interleave(enable)
 #pragma clang loop vectorize_predicate(enable)
+#pragma clang loop ivdep(enable)
 // CHECK-NEXT: while (i - 2 < Length)
   while (i - 2 < Length) {
     List[i] = i * 2;
     i++;
   }
 }
 
 template <int V, int I>

 }
 
 #ifdef MS_EXT
 #pragma init_seg(compiler)
 // MS-EXT: #pragma init_seg (.CRT$XCC){{$}}
 // MS-EXT-NEXT: int x = 3 __declspec(thread);
 int __declspec(thread) x = 3;
 #endif //MS_EXT
-

clang/test/CodeGenCXX/pragma-loop-ivdep.cpp

+// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -std=c++11 -emit-llvm -o - %s | FileCheck %s
+
+void test0(int *a, int *b, int LEN_1D) {
+  // CHECK-LABEL: @{{.*}}test0{{.*}}(
+  // CHECK: br label {{.*}}, !llvm.loop ![[LOOP0:.*]]
+
+#pragma clang loop vectorize(enable)
+  for (int i = 0; i < LEN_1D; i++)
+    a[b[i]] = a[b[i]] + 1;
+}
+
+void test1(int *a, int *b, int LEN_1D) {
+  // CHECK-LABEL: @{{.*}}test1{{.*}}(
+  // CHECK: br label {{.*}}, !llvm.loop ![[LOOP1:.*]]
+
+#pragma clang loop ivdep(enable)
+  for (int i = 0; i < LEN_1D; i++)
+    a[b[i]] = a[b[i]] + 1;
+}
+
+void test2(int *a, int *b, int LEN_1D) {
+  // CHECK-LABEL: @{{.*}}test2{{.*}}(
+  // CHECK: br label {{.*}}, !llvm.loop ![[LOOP2:.*]]
+
+#pragma clang loop vectorize(enable) ivdep(enable)
+  for (int i = 0; i < LEN_1D; i++)
+    a[b[i]] = a[b[i]] + 1;
+}
+
+// CHECK:      ![[LOOP0]] = distinct !{![[LOOP0]], !3}
+// CHECK-NEXT: !3 = !{!"llvm.loop.vectorize.enable", i1 true}
+// CHECK-NEXT: ![[LOOP1]] = distinct !{![[LOOP1]], !5, !3}
+// CHECK-NEXT: !5 = !{!"llvm.loop.vectorize.ivdep.enable", i1 true}
+// CHECK-NEXT: ![[LOOP2]] = distinct !{![[LOOP2]], !5, !3}

clang/test/Parser/pragma-loop.cpp

 }
 
 void test(int *List, int Length) {
   int i = 0;
 
 #pragma clang loop vectorize(enable)
 #pragma clang loop interleave(enable)
 #pragma clang loop vectorize_predicate(enable)
+#pragma clang loop ivdep(enable)
 #pragma clang loop unroll(full)
   while (i + 1 < Length) {
     List[i] = i;
   }
 
 #pragma clang loop vectorize_width(4)
 #pragma clang loop interleave_count(8)
 #pragma clang loop unroll_count(16)
#pragma clang loop distribute(disable)
 
   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 vectorize_predicate
 /* expected-error {{expected '('}} */ #pragma clang loop unroll
 /* expected-error {{expected '('}} */ #pragma clang loop distribute
+/* expected-error {{expected '('}} */ #pragma clang loop ivdep
 
 /* expected-error {{expected ')'}} */ #pragma clang loop vectorize(enable
 /* expected-error {{expected ')'}} */ #pragma clang loop interleave(enable
 /* expected-error {{expected ')'}} */ #pragma clang loop vectorize_predicate(enable
 /* expected-error {{expected ')'}} */ #pragma clang loop unroll(full
 /* expected-error {{expected ')'}} */ #pragma clang loop distribute(enable
+/* expected-error {{expected ')'}} */ #pragma clang loop ivdep(enable
 
 /* expected-error {{expected ')'}} */ #pragma clang loop vectorize_width(4
 /* expected-error {{expected ')'}} */ #pragma clang loop interleave_count(4
 /* expected-error {{expected ')'}} */ #pragma clang loop unroll_count(4
 
 /* 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, unroll_count, pipeline, pipeline_initiation_interval, vectorize_predicate, or distribute}} */ #pragma clang loop
+/* expected-error {{missing option; expected vectorize, vectorize_width, interleave, interleave_count, unroll, unroll_count, pipeline, pipeline_initiation_interval, vectorize_predicate, ivdep, 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)
 /* expected-warning {{extra tokens at end of '#pragma clang loop'}} */ #pragma clang loop vectorize(enable) ,
   while (i-4 < Length) {
     List[i] = i;
   }
 
/* expected-error {{use of undeclared identifier 'badvalue'}} */ #pragma clang loop unroll_count(badvalue)
   while (i-6 < Length) {
     List[i] = i;
   }
 
 /* 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)
+/* expected-error {{invalid argument; expected 'enable'}} */ #pragma clang loop ivdep(badidentifier)
   while (i-7 < Length) {
     List[i] = i;
   }
 
 // PR20069 - Loop pragma arguments that are not identifiers or numeric
 // constants crash FE.
 /* expected-error {{expected ')'}} */ #pragma clang loop vectorize(()
 /* expected-error {{invalid argument; expected 'enable', 'assume_safety' or 'disable'}} */ #pragma clang loop interleave(*)

clang/test/Parser/pragma-unroll-and-jam.cpp

 #pragma unroll(4)
   for (int i = 0; i < Length; i++) {
     for (int j = 0; j < Length; j++) {
       List[i * Length + j] = Value;
     }
   }
 
 // pragma clang unroll_and_jam is disabled for the moment
-/* expected-error {{invalid option 'unroll_and_jam'; expected vectorize, vectorize_width, interleave, interleave_count, unroll, unroll_count, pipeline, pipeline_initiation_interval, vectorize_predicate, or distribute}} */ #pragma clang loop unroll_and_jam(4)
+/* expected-error {{invalid option 'unroll_and_jam'; expected vectorize, vectorize_width, interleave, interleave_count, unroll, unroll_count, pipeline, pipeline_initiation_interval, vectorize_predicate, ivdep, or distribute}} */ #pragma clang loop unroll_and_jam(4)
   for (int i = 0; i < Length; i++) {
     for (int j = 0; j < Length; j++) {
       List[i * Length + j] = Value;
     }
   }
 
 #pragma unroll_and_jam
 /* expected-error {{expected statement}} */ }