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diff --git a/llvm/tools/llvm-mca/Pipeline.h b/llvm/tools/llvm-mca/Pipeline.h
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+//===--------------------- Pipeline.h ---------------------------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+/// \file
+///
+/// This file implements an ordered container of stages that simulate the
+/// pipeline of a hardware backend.
+///
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_TOOLS_LLVM_MCA_PIPELINE_H
+#define LLVM_TOOLS_LLVM_MCA_PIPELINE_H
+
+#include "Scheduler.h"
+#include "Stage.h"
+#include "llvm/ADT/SmallVector.h"
+
+namespace mca {
+
+class HWEventListener;
+class HWInstructionEvent;
+class HWStallEvent;
+
+/// A pipeline for a specific subtarget.
+///
+/// It emulates an out-of-order execution of instructions. Instructions are
+/// fetched from a MCInst sequence managed by an initial 'Fetch' stage.
+/// Instructions are firstly fetched, then dispatched to the schedulers, and
+/// then executed.
+///
+/// This class tracks the lifetime of an instruction from the moment where
+/// it gets dispatched to the schedulers, to the moment where it finishes
+/// executing and register writes are architecturally committed.
+/// In particular, it monitors changes in the state of every instruction
+/// in flight.
+///
+/// Instructions are executed in a loop of iterations. The number of iterations
+/// is defined by the SourceMgr object, which is managed by the initial stage
+/// of the instruction pipeline.
+///
+/// The Pipeline entry point is method 'run()' which executes cycles in a loop
+/// until there are new instructions to dispatch, and not every instruction
+/// has been retired.
+///
+/// Internally, the Pipeline collects statistical information in the form of
+/// histograms. For example, it tracks how the dispatch group size changes
+/// over time.
+class Pipeline {
+  /// An ordered list of stages that define this instruction pipeline.
+  llvm::SmallVector<std::unique_ptr<Stage>, 8> Stages;
+  std::set<HWEventListener *> Listeners;
+  unsigned Cycles;
+
+  bool executeStages(InstRef &IR);
+  void postExecuteStages(const InstRef &IR);
+  bool hasWorkToProcess();
+  void runCycle(unsigned Cycle);
+
+public:
+  Pipeline(unsigned DispatchWidth = 0, unsigned RegisterFileSize = 0,
+           unsigned LoadQueueSize = 0, unsigned StoreQueueSize = 0,
+           bool AssumeNoAlias = false)
+      : Cycles(0) {}
+  void appendStage(std::unique_ptr<Stage> S) { Stages.push_back(std::move(S)); }
+  void run();
+  void addEventListener(HWEventListener *Listener);
+  void notifyCycleBegin(unsigned Cycle);
+  void notifyInstructionEvent(const HWInstructionEvent &Event);
+  void notifyStallEvent(const HWStallEvent &Event);
+  void notifyResourceAvailable(const ResourceRef &RR);
+  void notifyReservedBuffers(llvm::ArrayRef<unsigned> Buffers);
+  void notifyReleasedBuffers(llvm::ArrayRef<unsigned> Buffers);
+  void notifyCycleEnd(unsigned Cycle);
+};
+} // namespace mca
+
+#endif // LLVM_TOOLS_LLVM_MCA_PIPELINE_H