llvm/lib/Target/AMDGPU/MCA/AMDGPUCustomBehaviour.h

   1 //===------------------- AMDGPUCustomBehaviour.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 defines the AMDGPUCustomBehaviour class which inherits from
  11 /// CustomBehaviour. This class is used by the tool llvm-mca to enforce
  12 /// target specific behaviour that is not expressed well enough in the
  13 /// scheduling model for mca to enforce it automatically.
  14 ///
  15 //===----------------------------------------------------------------------===//
  16
  17 #ifndef LLVM_LIB_TARGET_AMDGPU_MCA_AMDGPUCUSTOMBEHAVIOUR_H
  18 #define LLVM_LIB_TARGET_AMDGPU_MCA_AMDGPUCUSTOMBEHAVIOUR_H
  19
  20 #include "llvm/ADT/SmallVector.h"
  21 #include "llvm/MCA/CustomBehaviour.h"
  22 #include "llvm/TargetParser/TargetParser.h"
  23
  24 namespace llvm {
  25 namespace mca {
  26
  27 class AMDGPUInstrPostProcess : public InstrPostProcess {
  28   void processWaitCnt(std::unique_ptr<Instruction> &Inst, const MCInst &MCI);
  29
  30 public:
  31   AMDGPUInstrPostProcess(const MCSubtargetInfo &STI, const MCInstrInfo &MCII)
  32       : InstrPostProcess(STI, MCII) {}
  33
  34   ~AMDGPUInstrPostProcess() = default;
  35
  36   void postProcessInstruction(std::unique_ptr<Instruction> &Inst,
  37                               const MCInst &MCI) override;
  38 };
  39
  40 struct WaitCntInfo {
  41   bool VmCnt = false;
  42   bool ExpCnt = false;
  43   bool LgkmCnt = false;
  44   bool VsCnt = false;
  45 };
  46
  47 class AMDGPUCustomBehaviour : public CustomBehaviour {
  48   /// Whenever MCA would like to dispatch an s_waitcnt instructions,
  49   /// we must check all the instruction that are still executing to see if
  50   /// they modify the same CNT as we need to wait for. This vector
  51   /// gets built in the constructor and contains 1 WaitCntInfo struct
  52   /// for each instruction within the SrcManager. Each element
  53   /// tells us which CNTs that instruction may interact with.
  54   /// We conservatively assume some instructions interact with more
  55   /// CNTs than they do in reality, so we will occasionally wait
  56   /// longer than necessary, but we shouldn't ever wait for shorter.
  57   std::vector<WaitCntInfo> InstrWaitCntInfo;
  58
  59   /// This method gets called from the constructor and is
  60   /// where we setup the InstrWaitCntInfo vector.
  61   /// The core logic for determining which CNTs an instruction
  62   /// interacts with is taken from SIInsertWaitcnts::updateEventWaitcntAfter().
  63   /// Unfortunately, some of the logic from that function is not available to us
  64   /// in this scope so we conservatively end up assuming that some
  65   /// instructions interact with more CNTs than they do in reality.
  66   void generateWaitCntInfo();
  67   /// Helper function used in generateWaitCntInfo()
  68   bool hasModifiersSet(const std::unique_ptr<Instruction> &Inst,
  69                        unsigned OpName) const;
  70   /// Helper function used in generateWaitCntInfo()
  71   bool isGWS(uint16_t Opcode) const;
  72   /// Helper function used in generateWaitCntInfo()
  73   bool isAlwaysGDS(uint16_t Opcode) const;
  74   /// Helper function used in generateWaitCntInfo()
  75   bool isVMEM(const MCInstrDesc &MCID);
  76   /// This method gets called from checkCustomHazard when mca is attempting to
  77   /// dispatch an s_waitcnt instruction (or one of its variants). The method
  78   /// looks at each of the instructions that are still executing in the pipeline
  79   /// to determine if the waitcnt should force a wait.
  80   unsigned handleWaitCnt(ArrayRef<InstRef> IssuedInst, const InstRef &IR);
  81   /// Based on the type of s_waitcnt instruction we are looking at, and what its
  82   /// operands are, this method will set the values for each of the cnt
  83   /// references provided as arguments.
  84   void computeWaitCnt(const InstRef &IR, unsigned &Vmcnt, unsigned &Expcnt,
  85                       unsigned &Lgkmcnt, unsigned &Vscnt);
  86
  87 public:
  88   AMDGPUCustomBehaviour(const MCSubtargetInfo &STI,
  89                         const mca::SourceMgr &SrcMgr, const MCInstrInfo &MCII);
  90
  91   ~AMDGPUCustomBehaviour() = default;
  92   /// This method is used to determine if an instruction
  93   /// should be allowed to be dispatched. The return value is
  94   /// how many cycles until the instruction can be dispatched.
  95   /// This method is called after MCA has already checked for
  96   /// register and hardware dependencies so this method should only
  97   /// implement custom behaviour and dependencies that are not picked up
  98   /// by MCA naturally.
  99   unsigned checkCustomHazard(ArrayRef<InstRef> IssuedInst,
 100                              const InstRef &IR) override;
 101 };
 102 } // namespace mca
 103 } // namespace llvm
 104
 105 #endif