include/llvm/MCA/Pipeline.h

   1 //===--------------------- Pipeline.h ---------------------------*- C++ -*-===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8 /// \file
   9 ///
  10 /// This file implements an ordered container of stages that simulate the
  11 /// pipeline of a hardware backend.
  12 ///
  13 //===----------------------------------------------------------------------===//
  14
  15 #ifndef LLVM_MCA_PIPELINE_H
  16 #define LLVM_MCA_PIPELINE_H
  17
  18 #include "llvm/ADT/SmallVector.h"
  19 #include "llvm/MCA/HardwareUnits/Scheduler.h"
  20 #include "llvm/MCA/Stages/Stage.h"
  21 #include "llvm/Support/Error.h"
  22
  23 namespace llvm {
  24 namespace mca {
  25
  26 class HWEventListener;
  27
  28 /// A pipeline for a specific subtarget.
  29 ///
  30 /// It emulates an out-of-order execution of instructions. Instructions are
  31 /// fetched from a MCInst sequence managed by an initial 'Fetch' stage.
  32 /// Instructions are firstly fetched, then dispatched to the schedulers, and
  33 /// then executed.
  34 ///
  35 /// This class tracks the lifetime of an instruction from the moment where
  36 /// it gets dispatched to the schedulers, to the moment where it finishes
  37 /// executing and register writes are architecturally committed.
  38 /// In particular, it monitors changes in the state of every instruction
  39 /// in flight.
  40 ///
  41 /// Instructions are executed in a loop of iterations. The number of iterations
  42 /// is defined by the SourceMgr object, which is managed by the initial stage
  43 /// of the instruction pipeline.
  44 ///
  45 /// The Pipeline entry point is method 'run()' which executes cycles in a loop
  46 /// until there are new instructions to dispatch, and not every instruction
  47 /// has been retired.
  48 ///
  49 /// Internally, the Pipeline collects statistical information in the form of
  50 /// histograms. For example, it tracks how the dispatch group size changes
  51 /// over time.
  52 class Pipeline {
  53   Pipeline(const Pipeline &P) = delete;
  54   Pipeline &operator=(const Pipeline &P) = delete;
  55
  56   /// An ordered list of stages that define this instruction pipeline.
  57   SmallVector<std::unique_ptr<Stage>, 8> Stages;
  58   std::set<HWEventListener *> Listeners;
  59   unsigned Cycles;
  60
  61   Error runCycle();
  62   bool hasWorkToProcess();
  63   void notifyCycleBegin();
  64   void notifyCycleEnd();
  65
  66 public:
  67   Pipeline() : Cycles(0) {}
  68   void appendStage(std::unique_ptr<Stage> S);
  69
  70   /// Returns the total number of simulated cycles.
  71   Expected<unsigned> run();
  72
  73   void addEventListener(HWEventListener *Listener);
  74 };
  75 } // namespace mca
  76 } // namespace llvm
  77
  78 #endif // LLVM_MCA_PIPELINE_H