add pragmas to control Software Pipelining optimisation

[avl]

Summary

[PIPELINER] add two pragmas to control Software Pipelining optimisation.
    
  #pragma clang loop pipeline(disable)
    
      Disable SWP optimization for the next loop.
      “disable” is the only possible value.
    
  #pragma clang loop pipeline_initiation_interval(number)
    
      Set value of initiation interval for SWP
      optimization to specified number value for
      the next loop. Number is the positive value
      greater than 0.
    
  These pragmas could be used for debugging or reducing
  compile time purposes. It is possible to disable SWP for
  concrete loops to save compilation time or to find bugs
  by not doing SWP to certain loops. It is possible to set
  value of initiation interval to concrete number to save
  compilation time by not doing extra pipeliner passes or
  to check created schedule for specific initiation interval.

  That is clang part of the fix

[avl]

deleted small typo in CGLoopInfo.cpp

[aaron.ballman]

include/clang/Basic/Attr.td

2871–2872

Missing full stops at the end of the comments. Also, having read "for only 'Value' value", I'm still not certain what's happening. I think this is a count of some kind, so perhaps "Tries to pipeline 'Values' times." but I don't know what the verb "pipeline" means in this context.

Are users going to understand what the ii means in the user-facing name?

include/clang/Basic/AttrDocs.td

2583

Vector width, interleave count, unrolling count, and the initiation interval for pipelining can be explicitly specified.

2654

The disable state can only be specified for `#pragma clang loop pipeline`.

2663

Spell out ii

instructs software -> instructs the software

2664

to use only specified -> to use the specified

Remove the space before the colon as well.

Having read the docs, I would have no idea how to pick a value for the initiation interval. I'm still not even certain what it controls or does. Can you expand the documentation for that (feel free to link to other sources if there are authoritative places we can point the user to)?

2676

details including -> details, including

include/clang/Basic/DiagnosticParseKinds.td

1178

80-col

1192

Can you roll this into the above diagnostic with another %select, or does that make it too unreadable?

lib/CodeGen/CGLoopInfo.cpp

29

!Attrs.PipelineDisabled

127

Formatting is incorrect here (and below) -- you should run the patch through clang-format.

lib/CodeGen/CGLoopInfo.h

70

Missing full-stop. Here and elsewhere -- can you look at all the comments and make sure they're properly punctuated?

71

One good refactoring (don't feel obligated to do this) would be to use in-class initializers here.

test/Parser/pragma-pipeline.cpp

25

Can you add a few tests:

#pragma clang loop pipeline_ii_count(1 to show that we also diagnose the missing closing paren
#pragma clang loop pipeline_ii_count(1.0) to show that we diagnose a non-integer literal count
#pragma clang loop pipeline enable to show that we diagnose the missing open paren

[avl]

Ok, I will address all issues.

include/clang/Basic/Attr.td

2871–2872

As to ii - yes that should be understood by users, because it is important property of software pipelining optimization. Software Pipelining optimization tries to reorder instructions of original loop(from different iterations) so that resulting loop body takes less cycles. It started from some minimal value of ii and stopped with some maximal value. i.e. it tries to built schedule for min_ii, then min_ii+1, ... until schedule is found or until max_ii reached. If resulting value of ii already known then instead of searching in range min_ii, max_ii - it is possible to create schedule for already known ii.

probably following spelling would be better :

pipeline_ii_count: create loop schedule with initiation interval equals 'Value'

include/clang/Basic/DiagnosticParseKinds.td

1192

yes, it makes things too complicated. Though I could do it if necessary.

[aaron.ballman]

include/clang/Basic/Attr.td

2871–2872

because it is important property of software pipelining optimization.

My point is that I have no idea what "ii" means and I doubt I'll be alone -- does the "ii" differentiate this from other kinds of pipeline loop pragmas we plan to support, or is expected that "pipeline_ii_count" be the only pipeline count option? Can we drop the "ii" and not lose anything?

pipeline_ii_count: create loop schedule with initiation interval equals 'Value'

equals 'Value' -> equal to 'Value'

include/clang/Basic/DiagnosticParseKinds.td

1192

Not required, but I also didn't think the duplication here and below was a good approach either. But yeah, I'm not certain there's a better way to do this even if the list were rearranged.

[avl]

include/clang/Basic/Attr.td

2871–2872

Do you think spelling out ii would help ?

pipeline_initiation_interval(number)

[aaron.ballman]

include/clang/Basic/Attr.td

2871–2872

I think it would help. I'm less concerned about the internal names of things than I am for the user-facing identifiers and whether it will be understandable to people other than compiler and optimizer writers.

[hfinkel]

include/clang/Basic/Attr.td

2871–2872

Yes, I also think that it would help to spell this out.

[avl]

Ok, So thank you for the suggestions. I will implement that way.

[avl]

Please consider this change:

1. addressed style issues and formatted patch with clang-format
2. renamed pragma pipeline_ii_count to pipeline_initiation_interval
3. left LoopAttributes inclass initializers refactoring for some another fix :-)
4. added more tests

[aaron.ballman]

include/clang/Basic/AttrDocs.td

2673

"Check" -- check where? Perhaps "Search for" but I still don't think that's very satisfying for our documentation as there's no telling what users will find or how it relates (if at all) to this feature.

on optimisation -> on this optimization

I find this sentence doesn't really direct me to much of value (research presentations and class lectures, mostly), so I'd rather see the important details spelled out in our docs so that users don't have to guess as much.

2677–2678

There is nothing in the linked documentation that describes pipeline initiation intervals, so I'm still left wondering how to pick a value for the attribute argument. I think the docs need a bit more detail for what that value means and how it impacts the user's code.

[avl]

include/clang/Basic/AttrDocs.td

2673

I am just unsure which references to include here ... links to wikipedia or some concrete resources do not look good.

So you are suggesting to spell things out here... Ok, I will prepare short explanation...

[aaron.ballman]

include/clang/Basic/AttrDocs.td

2673

I am just unsure which references to include here ... links to wikipedia or some concrete resources do not look good.

If there's a definitive source for the information, like a research paper or a Wikipedia entry that does a great job explaining it, then feel free to link to it. We can always update dead links when they arise.

So you are suggesting to spell things out here... Ok, I will prepare short explanation...

If there's not a good place to link to that has the information, then yes, spelling it out would be great. Basically, someone reading these docs should have enough information available (directly or through links) to help them understand the feature even if it doesn't make them an expert in the topic. My concern with the docs right now is that I have no idea what value to put there (Does it have to be positive? Nonzero? Is there an upper bound?) because I can't find an explanation about what that value actually controls.

[avl]

include/clang/Basic/AttrDocs.td

2677–2678

How about this variant :

Software Pipelining optimization is a technique used to optimize loops by
utilizing instructions level parallelism. It reorders loop instructions to
overlap iterations. As the result new iteration started before previous
have finished. The Modulo Scheduling technique creates schedule for one
iteration such that when repeating at regular interval no inter-iteration
dependence violated. This constant interval(in cycles) between the start
of iterations called initiation interval. Cycles number of one iteration
of newly generated loop matches with Initiation Interval. For further
details see https://en.wikipedia.org/wiki/Software_pipelining and
"Swing Modulo Scheduling: A Lifetime-Sensitive Approach", by J. Llosa,
A. Gonzalez, E. Ayguade, and M. Valero.

`#pragma clang loop pipeline and #pragma loop pipeline_initiation_interval``
could be used as hints for Software Pipelining optimization.

Using `#pragma clang loop pipeline(disable)` avoids software pipelining optimization. The disable state can only be specified:

.. code-block:: c++

#pragma clang loop pipeline(disable)
for (...) {
  ...
}

Using `#pragma loop pipeline_initiation_interval`
instructs the software pipeliner to check the specified initiation interval.
If schedule found the result loop iteration would have specified
cycle count:

.. code-block:: c++

#pragma loop pipeline_initiation_interval(10)
for (...) {
  ...
}

[avl]

update documentation section.

[avl]

put a better link to doc

[aaron.ballman]

include/clang/Basic/AttrDocs.td

2650

instructions level -> instruction-level

2651

As a result, the next iteration starts before the previous iteration has finished.

2652–2654

The module scheduling technique creates a schedule for one iteration such that when repeating at regular intervals, no inter-iteration dependencies are violated.

2655

is called the initiation interval.

I can't quite parse the second sentence, though. Is it trying to say that the initiation interval is the number of cycles for a single iteration of the optimized loop?

2676

I'm can't quite parse this sentence either. Is it trying to say that the scheduler will try to find a loop iteration cycle count that most-closely matches the specified initiation interval?

2677

The initiation interval must be a positive number greater than zero.

[avl]

will correct all mistakes. please check explanations for the questions.

include/clang/Basic/AttrDocs.td

2655

Not quite right : initiation interval is not a number of cycles for a single iteration of the optimized loop. But initiation interval matches with number of cycles for a single iteration of the optimized loop. Initiation interval is the number of cycles between next and previous iteration of original loop. New loop created so that single iteration of the optimized loop has the same number cycles as initiation interval( thus every new iteration of original loop started each time when new iteration of optimized loop started - difference between iterations is initiation interval).

trying to rephrase : number of cycles for a single iteration of the optimized loop matches with number of cycles of initiation interval.

2676

I wanted to say that pipeliner will try to find a schedule that exactly matches the specified initiation interval. And if schedule would be found then single iteration of the optimized loop would have exactly the same amount of cycles as initiation interval. trying to rephrase :

If schedule would be found then single iteration of the optimized loop would have exactly the same amount of cycles as initiation interval has.

[aaron.ballman]

Adding @tonic as a reviewer, who may have suggestions on how to improve the documentation wording.

include/clang/Basic/AttrDocs.td

2655

I am still a bit fuzzy on the details (optimizations are not my area of expertise). Is this an accurate what to rephrase it?

"The initiation interval is the number of cycles between two iterations of an unoptimized loop. These pragmas cause a new. optimized loop to be created such that a single iteration of the loop executes in the same number of cycles as the initiation interval."

2676

Ah, okay! So what happens if an exact match cannot be found? Does it behave as though the pragma was not specified at all (as in, the pragma is ignored)?

[avl]

include/clang/Basic/AttrDocs.td

2655

I will take it with small modifications.

2676

yes. if schedule was not found then the loop would stay unchanged.

[avl]

please consider changes in AttrDocs.td

[aaron.ballman]

The docs are getting much closer -- just a few grammatical things left to fix, I believe.

include/clang/Basic/AttrDocs.td

2582–2584

Can you combine the new sentence with the previous one? The directive allows vectorization, interleaving, pipelining, and unrolling to be enabled or disabled.

2657

in newly created schedule -> in the newly created schedule

New optimized loop -> A new, optimized loop

2662

for Software Pipelining optimization. -> for the software pipelining optimization.

2663

or c++11 range-based for loop. -> or a C++11 range-based for loop.

2666

avoids software -> avoids the software

2678

If schedule was found -> If a schedule was found

2679

would have specified cycle count. -> would have the specified cycle count.

If schedule was not -> If a schedule was not
would stay -> remains

[avl]

include/clang/Basic/AttrDocs.td

2582–2584

In that case it would change a meaning and become incorrect. Pipelining could only be disabled. It could not be enabled.

[avl]

Thank you. addressed all grammar things. please check it once more.

[aaron.ballman]

include/clang/Basic/AttrDocs.td

2582–2584

Ah, yes, that would change the meaning then. I'd go with: The directive allows pipelining to be disabled, or vectorization, interleaving, and unrolling to be enabled or disabled.

2663

I'd like to see a Sema test where the pragma is put at global scope to see if the diagnostic is reasonable or not. e.g.,

#pragma clang loop pipeline(disable)

int main() {
  for (int i = 0; i < 10; ++i)
    ;
}

2680–2681

Please add a Sema test with a negative number as the initiation interval.

include/clang/Basic/DiagnosticParseKinds.td

1179

pipeline_initiation_interval or distribute -> pipeline_initiation_interval, or distribute

(Keeps the Oxford comma as in the original diagnostic.)

test/Parser/pragma-pipeline.cpp

29

This isn't really a parser test -- it should probably be in Sema instead.

36–48

These should also move to Sema.

[avl]

Thank you. I updated doc, splitted Parser test, added Sema tests. Please check it once more.

[aaron.ballman]

test/Sema/pragma-pipeline.cpp

3 ↗

(On Diff #179933)

I think this error is pretty unfortunate -- it doesn't really help the user to understand what's wrong with their code. Can it be improved?

[avl]

test/Sema/pragma-pipeline.cpp

3 ↗

(On Diff #179933)

Agreed, this does not look very informative. It surely can be improved. Though it looks like not related to my fix. My fix is to add two additional loop hints. That kind of diagnostic related to all loop hints "clang loop". I.e. all pragmas "clang loop" can be checked for various cases and for better diagnostic. It looks like separate task. But OK, I will check that case.

[aaron.ballman]

LGTM!

test/Sema/pragma-pipeline.cpp

3 ↗

(On Diff #179933)

That's a fair point -- I'm fine with doing that work in a separate patch. I don't think we need to hold this patch up further for it, anyway.

[avl]

Thank you! Aaron, Could you integrate this patch, please? I do not have commit access yet.

[aaron.ballman]

I commit this in r350414, thank you for the patch!

include/clang/Basic/Attr.td

def LoopHint : Attr {
   /// vectorize_width: vectorize loop operations with width 'Value'.
   /// interleave: interleave multiple loop iterations if State == Enable.
   /// interleave_count: interleaves 'Value' loop iterations.
   /// unroll: fully unroll loop if State == Enable.
   /// unroll_count: unrolls loop 'Value' times.
   /// unroll_and_jam: attempt to unroll and jam loop if State == Enable.
   /// unroll_and_jam_count: unroll and jams loop 'Value' times.
   /// distribute: attempt to distribute loop if State == Enable
+  /// pipeline: disable pipelining loop if State == Disable
+  /// pipeline_ii_count: try to pipeline loop for only 'Value' value
 
   /// #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">, 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",
-                           "distribute"],
+                           "pipeline", "pipeline_ii_count", "distribute"],
                           ["Vectorize", "VectorizeWidth", "Interleave", "InterleaveCount",
                            "Unroll", "UnrollCount", "UnrollAndJam", "UnrollAndJamCount",
-                           "Distribute"]>,
+                           "PipelineDisabled", "PipelineIICount", "Distribute"]>,
               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 PipelineIICount: return "pipeline_ii_count";
     case Distribute: return "distribute";
     }
     llvm_unreachable("Unhandled LoopHint option.");
   }
 
   void printPrettyPragma(raw_ostream &OS, const PrintingPolicy &Policy) const {
     unsigned SpellingIndex = getSpellingListIndex();
     // For "#pragma unroll" and "#pragma nounroll" the string "unroll" or

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 vectorization,
-interleaving, and unrolling to be enabled or disabled. Vector width as well
-as interleave and unrolling count can be manually specified. See
-`language extensions
+interleaving, and unrolling to be enabled or disabled. Pipelining could be disabled.
+Vector width as well as interleave, unrolling count and Initiation interval for pipelining
+can be manually 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";

 ``#pragma clang loop unroll_count(_value_)`` respectively. ``#pragma nounroll``
 is equivalent to ``#pragma clang loop unroll(disable)``.  See
 `language extensions
 <http://clang.llvm.org/docs/LanguageExtensions.html#extensions-for-loop-hint-optimizations>`_
 for further details including limitations of the unroll hints.
   }];
 }
 
+def PipelineHintDocs : Documentation {
+  let Category = DocCatStmt;
+  let Heading = "#pragma clang loop pipeline, #pragma clang loop pipeline_ii_count";
+  let Content = [{
+Loop pipelining optimization hints can be specified with ``#pragma clang loop pipeline`` and
+``#pragma loop pipeline_ii_count``. The pragma is placed immediately before a for, while,
+do-while, or c++11 range-based for loop.
+
+Specifying ``#pragma clang loop pipeline(disable)`` avoids software pipelining optimization.
+Only `disable` state could be specified for ``#pragma clang loop pipeline``:
+
+.. code-block:: c++
+
+  #pragma clang loop pipeline(disable)
+  for (...) {
+    ...
+  }
+
+Specifying the ii count parameter for ``#pragma loop pipeline_ii_count`` instructs software
+pipeliner to use only specified initiation interval :
+
+.. code-block:: c++
+
+  #pragma loop pipeline_ii_count(10)
+  for (...) {
+    ...
+  }
+
+See
+`language extensions
+<http://clang.llvm.org/docs/LanguageExtensions.html#extensions-for-loop-hint-optimizations>`_
+for further details including limitations of the pipeline hints.
+  }];
+}
+
+
+
 def OpenCLUnrollHintDocs : Documentation {
   let Category = DocCatStmt;
   let Content = [{
 The opencl_unroll_hint attribute qualifier can be used to specify that a loop
 (for, while and do loops) can be unrolled. This attribute qualifier can be
 used to specify full unrolling or partial unrolling by a specified amount.
 This is a compiler hint and the compiler may ignore this directive. See
 `OpenCL v2.0 <https://www.khronos.org/registry/cl/specs/opencl-2.0.pdf>`_

include/clang/Basic/DiagnosticParseKinds.td

def err_omp_expected_clause: Error<
   "expected at least one clause on '#pragma omp %0' directive">;
 
 // 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, or distribute">;
+  "vectorize_width, interleave, interleave_count, unroll, unroll_count, pipeline, pipeline_ii_count 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'">;
 
 // 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">,

lib/CodeGen/CGLoopInfo.h

struct LoopAttributes {
   /// llvm.unroll.
   unsigned UnrollCount;
 
   /// llvm.unroll.
   unsigned UnrollAndJamCount;
 
   /// Value for llvm.loop.distribute.enable metadata.
   LVEnableState DistributeEnable;
+
+  /// Value for llvm.loop.pipeline.disable metadata
+  bool PipelineDisabled;
+
+  /// Value for llvm.loop.pipeline.iicount metadata
+  unsigned PipelineIICount;
 };
 
 /// Information used when generating a structured loop.
 class LoopInfo {
 public:
   /// Construct a new LoopInfo for the loop with entry Header.
   LoopInfo(llvm::BasicBlock *Header, const LoopAttributes &Attrs,
            const llvm::DebugLoc &StartLoc, const llvm::DebugLoc &EndLoc);
public:
   void setInterleaveCount(unsigned C) { StagedAttrs.InterleaveCount = C; }
 
   /// Set the unroll count for the next loop pushed.
   void setUnrollCount(unsigned C) { StagedAttrs.UnrollCount = C; }
 
   /// \brief Set the unroll count for the next loop pushed.
   void setUnrollAndJamCount(unsigned C) { StagedAttrs.UnrollAndJamCount = C; }
 
+  /// Set the pipeline disabled state
+  void setPipelineDisabled(bool S) { StagedAttrs.PipelineDisabled = S; }
+
+  /// Set the pipeline ii count
+  void setPipelineIICount(unsigned C) { StagedAttrs.PipelineIICount = C; }
+
 private:
   /// Returns true if there is LoopInfo on the stack.
   bool hasInfo() const { return !Active.empty(); }
   /// Return the LoopInfo for the current loop. HasInfo should be called
   /// first to ensure LoopInfo is present.
   const LoopInfo &getInfo() const { return Active.back(); }
   /// The set of attributes that will be applied to the next pushed loop.
   LoopAttributes StagedAttrs;
   /// Stack of active loops.
   llvm::SmallVector<LoopInfo, 4> Active;
 };
 
 } // end namespace CodeGen
 } // end namespace clang
 
 #endif

lib/CodeGen/CGLoopInfo.cpp

 
 static MDNode *createMetadata(LLVMContext &Ctx, const LoopAttributes &Attrs,
                               const llvm::DebugLoc &StartLoc,
                               const llvm::DebugLoc &EndLoc) {
 
   if (!Attrs.IsParallel && Attrs.VectorizeWidth == 0 &&
       Attrs.InterleaveCount == 0 && Attrs.UnrollCount == 0 &&
       Attrs.UnrollAndJamCount == 0 &&
+      Attrs.PipelineDisabled == false &&
+      Attrs.PipelineIICount == 0 &&
       Attrs.VectorizeEnable == LoopAttributes::Unspecified &&
       Attrs.UnrollEnable == LoopAttributes::Unspecified &&
       Attrs.UnrollAndJamEnable == LoopAttributes::Unspecified &&
       Attrs.DistributeEnable == LoopAttributes::Unspecified && !StartLoc &&
       !EndLoc)
     return nullptr;
 
   SmallVector<Metadata *, 4> Args;
static MDNode *createMetadata(LLVMContext &Ctx, const LoopAttributes &Attrs,
   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));
   }
 
+  if(Attrs.PipelineDisabled){
+      Metadata *Vals[] = {MDString::get(Ctx, "llvm.loop.pipeline.disable"),
+                          ConstantAsMetadata::get(ConstantInt::get(
+                              Type::getInt1Ty(Ctx), (Attrs.PipelineDisabled == true)))};
+      Args.push_back(MDNode::get(Ctx, Vals));
+  }
+
+  if(Attrs.PipelineIICount > 0){
+      Metadata *Vals[] = {MDString::get(Ctx, "llvm.loop.pipeline.iicount"),
+                          ConstantAsMetadata::get(ConstantInt::get(
+                              Type::getInt32Ty(Ctx), Attrs.PipelineIICount))};
+      Args.push_back(MDNode::get(Ctx, Vals));
+  }
+
   // Set the first operand to itself.
   MDNode *LoopID = MDNode::get(Ctx, Args);
   LoopID->replaceOperandWith(0, LoopID);
   return LoopID;
 }
 
 LoopAttributes::LoopAttributes(bool IsParallel)
     : IsParallel(IsParallel), VectorizeEnable(LoopAttributes::Unspecified),
       UnrollEnable(LoopAttributes::Unspecified),
       UnrollAndJamEnable(LoopAttributes::Unspecified), VectorizeWidth(0),
       InterleaveCount(0), UnrollCount(0), UnrollAndJamCount(0),
-      DistributeEnable(LoopAttributes::Unspecified) {}
+      DistributeEnable(LoopAttributes::Unspecified),
+      PipelineDisabled(false), PipelineIICount(0) {}
 
 void LoopAttributes::clear() {
   IsParallel = false;
   VectorizeWidth = 0;
   InterleaveCount = 0;
   UnrollCount = 0;
   UnrollAndJamCount = 0;
   VectorizeEnable = LoopAttributes::Unspecified;
   UnrollEnable = LoopAttributes::Unspecified;
   UnrollAndJamEnable = LoopAttributes::Unspecified;
   DistributeEnable = LoopAttributes::Unspecified;
+  PipelineDisabled = false;
+  PipelineIICount = 0;
 }
 
 LoopInfo::LoopInfo(BasicBlock *Header, const LoopAttributes &Attrs,
                    const llvm::DebugLoc &StartLoc, const llvm::DebugLoc &EndLoc)
     : LoopID(nullptr), Header(Header), Attrs(Attrs) {
   LoopID = createMetadata(Header->getContext(), Attrs, StartLoc, EndLoc);
 }
 
case LoopHintAttr::Disable:
         setUnrollState(LoopAttributes::Disable);
         break;
       case LoopHintAttr::UnrollAndJam:
         setUnrollAndJamState(LoopAttributes::Disable);
         break;
       case LoopHintAttr::Distribute:
         setDistributeState(false);
         break;
+      case LoopHintAttr::PipelineDisabled:
+        setPipelineDisabled(true);
+        break;
       case LoopHintAttr::UnrollCount:
       case LoopHintAttr::UnrollAndJamCount:
       case LoopHintAttr::VectorizeWidth:
       case LoopHintAttr::InterleaveCount:
+      case LoopHintAttr::PipelineIICount:
         llvm_unreachable("Options cannot be disabled.");
         break;
       }
       break;
     case LoopHintAttr::Enable:
       switch (Option) {
       case LoopHintAttr::Vectorize:
       case LoopHintAttr::Interleave:
         setVectorizeEnable(true);
         break;
       case LoopHintAttr::Unroll:
         setUnrollState(LoopAttributes::Enable);
         break;
       case LoopHintAttr::UnrollAndJam:
         setUnrollAndJamState(LoopAttributes::Enable);
         break;
       case LoopHintAttr::Distribute:
         setDistributeState(true);
         break;
+      break;
       case LoopHintAttr::UnrollCount:
       case LoopHintAttr::UnrollAndJamCount:
       case LoopHintAttr::VectorizeWidth:
       case LoopHintAttr::InterleaveCount:
+      case LoopHintAttr::PipelineDisabled:
+      case LoopHintAttr::PipelineIICount:
         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::UnrollCount:
       case LoopHintAttr::UnrollAndJamCount:
       case LoopHintAttr::VectorizeWidth:
       case LoopHintAttr::InterleaveCount:
       case LoopHintAttr::Distribute:
+      case LoopHintAttr::PipelineDisabled:
+      case LoopHintAttr::PipelineIICount:
         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::UnrollCount:
       case LoopHintAttr::UnrollAndJamCount:
       case LoopHintAttr::VectorizeWidth:
       case LoopHintAttr::InterleaveCount:
       case LoopHintAttr::Distribute:
+      case LoopHintAttr::PipelineDisabled:
+      case LoopHintAttr::PipelineIICount:
         llvm_unreachable("Options cannot be used with 'full' hint.");
         break;
       }
       break;
     case LoopHintAttr::Numeric:
       switch (Option) {
       case LoopHintAttr::VectorizeWidth:
         setVectorizeWidth(ValueInt);
         break;
       case LoopHintAttr::InterleaveCount:
         setInterleaveCount(ValueInt);
         break;
       case LoopHintAttr::UnrollCount:
         setUnrollCount(ValueInt);
         break;
       case LoopHintAttr::UnrollAndJamCount:
         setUnrollAndJamCount(ValueInt);
         break;
+      case LoopHintAttr::PipelineIICount:
+        setPipelineIICount(ValueInt);
+        break;
       case LoopHintAttr::Unroll:
       case LoopHintAttr::UnrollAndJam:
       case LoopHintAttr::Vectorize:
       case LoopHintAttr::Interleave:
       case LoopHintAttr::Distribute:
+      case LoopHintAttr::PipelineDisabled:
         llvm_unreachable("Options cannot be assigned a value.");
         break;
       }
       break;
     }
   }
 
   /// Stage the attributes.

lib/Parse/ParsePragma.cpp

bool Parser::HandlePragmaLoopHint(LoopHint &Hint) {
   // the TokSize by 1.
   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 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");
     StateOption = llvm::StringSwitch<bool>(OptionInfo->getName())
                       .Case("vectorize", true)
                       .Case("interleave", true)
                       .Default(false) ||
-                  OptionUnroll || OptionUnrollAndJam || OptionDistribute;
+                  OptionUnroll || OptionUnrollAndJam ||
+                  OptionDistribute || OptionPipelineDisabled;
   }
 
   bool AssumeSafetyArg =
-      !OptionUnroll && !OptionUnrollAndJam && !OptionDistribute;
+      !OptionUnroll && !OptionUnrollAndJam && !OptionDistribute && !OptionPipelineDisabled;
   // 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())
-                         .Cases("enable", "disable", true)
+                         .Case("disable", true)
+                         .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 {
         Diag(Toks[0].getLocation(), diag::err_pragma_invalid_keyword)
             << /*FullKeyword=*/(OptionUnroll || OptionUnrollAndJam)
             << /*AssumeSafetyKeyword=*/AssumeSafetyArg;
+      }
       return false;
     }
     if (Toks.size() > 2)
       Diag(Tok.getLocation(), diag::warn_pragma_extra_tokens_at_eol)
           << PragmaLoopHintString(Info->PragmaName, Info->Option);
     Hint.StateLoc = IdentifierLoc::create(Actions.Context, StateLoc, StateInfo);
   } else {
     // Enter constant expression including eof terminator into token stream.

 ///
 ///  loop-hint:
 ///    'vectorize' '(' loop-hint-keyword ')'
 ///    'interleave' '(' loop-hint-keyword ')'
 ///    'unroll' '(' unroll-hint-keyword ')'
 ///    'vectorize_width' '(' loop-hint-value ')'
 ///    'interleave_count' '(' loop-hint-value ')'
 ///    'unroll_count' '(' loop-hint-value ')'
+///    'pipeline' '(' disable ')'
+///    'pipeline_ii_count' '(' loop-hint-value ')'
 ///
 ///  loop-hint-keyword:
 ///    'enable'
 ///    'disable'
 ///    'assume_safety'
 ///
 ///  unroll-hint-keyword:
 ///    'enable'
while (Tok.is(tok::identifier)) {
     bool OptionValid = llvm::StringSwitch<bool>(OptionInfo->getName())
                            .Case("vectorize", true)
                            .Case("interleave", true)
                            .Case("unroll", true)
                            .Case("distribute", true)
                            .Case("vectorize_width", true)
                            .Case("interleave_count", true)
                            .Case("unroll_count", true)
+                           .Case("pipeline", true)
+                           .Case("pipeline_ii_count", true)
                            .Default(false);
     if (!OptionValid) {
       PP.Diag(Tok.getLocation(), diag::err_pragma_loop_invalid_option)
           << /*MissingOption=*/false << OptionInfo;
       return;
     }
     PP.Lex(Tok);
 

lib/Sema/SemaStmtAttr.cpp

if (PragmaNoUnroll) {
     Option = llvm::StringSwitch<LoopHintAttr::OptionType>(
                  OptionLoc->Ident->getName())
                  .Case("vectorize", LoopHintAttr::Vectorize)
                  .Case("vectorize_width", LoopHintAttr::VectorizeWidth)
                  .Case("interleave", LoopHintAttr::Interleave)
                  .Case("interleave_count", LoopHintAttr::InterleaveCount)
                  .Case("unroll", LoopHintAttr::Unroll)
                  .Case("unroll_count", LoopHintAttr::UnrollCount)
+                 .Case("pipeline", LoopHintAttr::PipelineDisabled)
+                 .Case("pipeline_ii_count", LoopHintAttr::PipelineIICount)
                  .Case("distribute", LoopHintAttr::Distribute)
                  .Default(LoopHintAttr::Vectorize);
     if (Option == LoopHintAttr::VectorizeWidth ||
         Option == LoopHintAttr::InterleaveCount ||
-        Option == LoopHintAttr::UnrollCount) {
+        Option == LoopHintAttr::UnrollCount ||
+        Option == LoopHintAttr::PipelineIICount
+        ) {
       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::Unroll ||
-               Option == LoopHintAttr::Distribute) {
+               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;
       else if (StateLoc->Ident->isStr("full"))
         State = LoopHintAttr::Full;
       else if (StateLoc->Ident->isStr("enable"))
         State = LoopHintAttr::Enable;
       else
         llvm_unreachable("bad loop hint argument");
     } else
       llvm_unreachable("bad loop hint");
   }
 
   return LoopHintAttr::CreateImplicit(S.Context, Spelling, Option, State,
                                       ValueExpr, A.getRange());
 }
 
 static void
 CheckForIncompatibleAttributes(Sema &S,
                                const SmallVectorImpl<const Attr *> &Attrs) {
-  // There are 5 categories of loop hints attributes: vectorize, interleave,
-  // unroll, unroll_and_jam and distribute. Except for distribute they come
+  // There are 6 categories of loop hints attributes: vectorize, interleave,
+  // unroll, unroll_and_jam, pipeline 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},
                    {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, Unroll, UnrollAndJam, Distribute } Category;
+    enum { Vectorize, Interleave, Unroll, UnrollAndJam, Distribute, Pipeline } Category;
     switch (Option) {
     case LoopHintAttr::Vectorize:
     case LoopHintAttr::VectorizeWidth:
       Category = Vectorize;
       break;
     case LoopHintAttr::Interleave:
     case LoopHintAttr::InterleaveCount:
       Category = Interleave;
       break;
     case LoopHintAttr::Unroll:
     case LoopHintAttr::UnrollCount:
       Category = Unroll;
       break;
     case LoopHintAttr::UnrollAndJam:
     case LoopHintAttr::UnrollAndJamCount:
       Category = UnrollAndJam;
       break;
     case LoopHintAttr::Distribute:
       // Perform the check for duplicated 'distribute' hints.
       Category = Distribute;
       break;
+    case LoopHintAttr::PipelineDisabled:
+    case LoopHintAttr::PipelineIICount:
+      Category = Pipeline;
+      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::UnrollAndJam ||
+        Option == LoopHintAttr::PipelineDisabled ||
         Option == LoopHintAttr::Distribute) {
       // Enable|Disable|AssumeSafety hint.  For example, vectorize(enable).
       PrevAttr = CategoryState.StateAttr;
       CategoryState.StateAttr = LH;
     } else {
       // Numeric hint.  For example, vectorize_width(8).
       PrevAttr = CategoryState.NumericAttr;
       CategoryState.NumericAttr = LH;

test/CodeGenCXX/pragma-pipeline.cpp

+// RUN: %clang_cc1 -triple hexagon -std=c++11 -emit-llvm -o - %s | FileCheck %s
+
+void pipeline_disabled(int *List, int Length, int Value) {
+  // CHECK-LABEL: define {{.*}} @_Z17pipeline_disabled 
+#pragma clang loop pipeline(disable) 
+  for (int i = 0; i < Length; i++) {
+      // CHECK: br label {{.*}}, !llvm.loop ![[LOOP_1:.*]]
+      List[i] = Value;
+  }
+}
+
+void pipeline_not_disabled(int *List, int Length, int Value) {
+  // CHECK-LABEL: define {{.*}} @_Z21pipeline_not_disabled 
+  for (int i = 0; i < Length; i++) {
+      List[i] = Value;
+  }
+}
+
+void pipeline_ii_count(int *List, int Length, int Value) {
+  // CHECK-LABEL: define {{.*}} @_Z17pipeline_ii_count
+#pragma clang loop pipeline_ii_count(10) 
+  for (int i = 0; i < Length; i++) {
+      // CHECK: br label {{.*}}, !llvm.loop ![[LOOP_3:.*]]
+      List[i] = Value;
+  }
+}
+
+void pipeline_disabled_on_nested_loop(int *List, int Length, int Value) {
+  // CHECK-LABEL: define {{.*}} @_Z32pipeline_disabled_on_nested_loop
+  for (int i = 0; i < Length; i++) {
+#pragma clang loop pipeline(disable)    
+    for (int j = 0; j < Length; j++) { 
+      // CHECK: br label {{.*}}, !llvm.loop ![[LOOP_4:.*]]
+      List[i*Length + j] = Value;
+    }
+  }
+}
+
+// CHECK: ![[LOOP_1]] = distinct !{![[LOOP_1]], ![[PIPELINE_DISABLE:.*]]}
+// CHECK: ![[PIPELINE_DISABLE]] = !{!"llvm.loop.pipeline.disable", i1 true}
+
+// CHECK-NOT:llvm.loop.pipeline
+
+// CHECK: ![[LOOP_3]] = distinct !{![[LOOP_3]], ![[PIPELINE_II_10:.*]]}
+// CHECK: ![[PIPELINE_II_10]] = !{!"llvm.loop.pipeline.iicount", i32 10}
+
+// CHECK: ![[LOOP_4]] = distinct !{![[LOOP_4]], ![[PIPELINE_DISABLE]]}

test/Parser/pragma-loop.cpp

 /* 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, or distribute}} */ #pragma clang loop
+/* expected-error {{missing option; expected vectorize, vectorize_width, interleave, interleave_count, unroll, unroll_count, pipeline, pipeline_ii_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)
 /* expected-warning {{extra tokens at end of '#pragma clang loop'}} */ #pragma clang loop vectorize(enable) ,
   while (i-4 < Length) {
     List[i] = i;
   }
 

test/Parser/pragma-pipeline.cpp

+// RUN: %clang_cc1 -std=c++11 -verify %s
+
+// Note that this puts the expected lines before the directives to work around
+// limitations in the -verify mode.
+
+void test(int *List, int Length, int Value) {
+  int i = 0;
+
+#pragma clang loop pipeline(disable) 
+  for (int i = 0; i < Length; i++) {
+      List[i] = Value;
+  }
+
+#pragma clang loop pipeline_ii_count(10) 
+  for (int i = 0; i < Length; i++) {
+      List[i] = Value;
+  }
+
+/* expected-error {{expected ')'}} */ #pragma clang loop pipeline(disable
+/* expected-error {{invalid argument; expected 'disable'}} */ #pragma clang loop pipeline(enable)
+/* expected-error {{invalid argument; expected 'disable'}} */ #pragma clang loop pipeline(error)
+/* expected-error {{missing argument; expected an integer value}} */ #pragma clang loop pipeline_ii_count()
+/* expected-error {{use of undeclared identifier 'error'}} */ #pragma clang loop pipeline_ii_count(error)
+/* expected-error {{expected '('}} */ #pragma clang loop pipeline_ii_count 1 2
+  for (int i = 0; i < Length; i++) {
+    for (int j = 0; j < Length; j++) {
+      List[i * Length + j] = Value;
+    }
+  }
+
+#pragma clang loop pipeline(disable) 
+/* expected-error {{expected a for, while, or do-while loop to follow '#pragma clang loop'}} */ int j = Length;
+#pragma clang loop pipeline_ii_count(4) 
+/* expected-error {{expected a for, while, or do-while loop to follow '#pragma clang loop'}} */ int k = Length;
+
+#pragma clang loop pipeline(disable)
+#pragma clang loop pipeline_ii_count(4) /* expected-error {{incompatible directives 'pipeline(disable)' and 'pipeline_ii_count(4)'}} */
+  for (int i = 0; i < Length; i++) {
+      List[i] = Value;
+  }
+
+#pragma clang loop pipeline(disable) 
+/* expected-error {{expected statement}} */ }

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, 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_ii_count 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}} */ }