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diff --git a/llvm/lib/Target/AMDGPU/MCA/AMDGPUCustomBehaviour.h b/llvm/lib/Target/AMDGPU/MCA/AMDGPUCustomBehaviour.h
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+++ b/llvm/lib/Target/AMDGPU/MCA/AMDGPUCustomBehaviour.h
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+//===------------------- AMDGPUCustomBehaviour.h ----------------*-C++ -* -===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+/// \file
+///
+/// This file defines the AMDGPUCustomBehaviour class which inherits from
+/// CustomBehaviour. This class is used by the tool llvm-mca to enforce
+/// target specific behaviour that is not expressed well enough in the
+/// scheduling model for mca to enforce it automatically.
+///
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIB_TARGET_AMDGPU_MCA_AMDGPUCUSTOMBEHAVIOUR_H
+#define LLVM_LIB_TARGET_AMDGPU_MCA_AMDGPUCUSTOMBEHAVIOUR_H
+
+#include "llvm/ADT/SmallVector.h"
+#include "llvm/MCA/CustomBehaviour.h"
+#include "llvm/Support/TargetParser.h"
+
+namespace llvm {
+namespace mca {
+
+class AMDGPUInstrPostProcess : public InstrPostProcess {
+  void processWaitCnt(std::unique_ptr<Instruction> &Inst, const MCInst &MCI);
+
+public:
+  AMDGPUInstrPostProcess(const MCSubtargetInfo &STI, const MCInstrInfo &MCII)
+      : InstrPostProcess(STI, MCII) {}
+
+  ~AMDGPUInstrPostProcess() {}
+
+  void postProcessInstruction(std::unique_ptr<Instruction> &Inst,
+                              const MCInst &MCI) override;
+};
+
+struct WaitCntInfo {
+  bool VmCnt = false;
+  bool ExpCnt = false;
+  bool LgkmCnt = false;
+  bool VsCnt = false;
+};
+
+class AMDGPUCustomBehaviour : public CustomBehaviour {
+  /// Whenever MCA would like to dispatch an s_waitcnt instructions,
+  /// we must check all the instruction that are still executing to see if
+  /// they modify the same CNT as we need to wait for. This vector
+  /// gets built in the constructor and contains 1 WaitCntInfo struct
+  /// for each instruction within the SrcManager. Each element
+  /// tells us which CNTs that instruction may interact with.
+  /// We conservatively assume some instructions interact with more
+  /// CNTs than they do in reality, so we will occasionally wait
+  /// longer than necessary, but we shouldn't ever wait for shorter.
+  std::vector<WaitCntInfo> InstrWaitCntInfo;
+
+  /// This method gets called from the constructor and is
+  /// where we setup the InstrWaitCntInfo vector.
+  /// The core logic for determining which CNTs an instruction
+  /// interacts with is taken from SIInsertWaitcnts::updateEventWaitcntAfter().
+  /// Unfortunately, some of the logic from that function is not available to us
+  /// in this scope so we conservatively end up assuming that some
+  /// instructions interact with more CNTs than they do in reality.
+  void generateWaitCntInfo();
+  /// Helper function used in generateWaitCntInfo()
+  bool hasModifiersSet(const std::unique_ptr<Instruction> &Inst,
+                       unsigned OpName) const;
+  /// Helper function used in generateWaitCntInfo()
+  bool isAlwaysGDS(uint16_t Opcode) const;
+  /// Helper function used in generateWaitCntInfo()
+  bool isVMEM(const MCInstrDesc &MCID);
+  /// This method gets called from checkCustomHazard when mca is attempting to
+  /// dispatch an s_waitcnt instruction (or one of its variants). The method
+  /// looks at each of the instructions that are still executing in the pipeline
+  /// to determine if the waitcnt should force a wait.
+  unsigned handleWaitCnt(ArrayRef<InstRef> IssuedInst, const InstRef &IR);
+  /// Based on the type of s_waitcnt instruction we are looking at, and what its
+  /// operands are, this method will set the values for each of the cnt
+  /// references provided as arguments.
+  void computeWaitCnt(const InstRef &IR, unsigned &Vmcnt, unsigned &Expcnt,
+                      unsigned &Lgkmcnt, unsigned &Vscnt);
+
+public:
+  AMDGPUCustomBehaviour(const MCSubtargetInfo &STI,
+                        const mca::SourceMgr &SrcMgr, const MCInstrInfo &MCII);
+
+  ~AMDGPUCustomBehaviour() {}
+  /// This method is used to determine if an instruction
+  /// should be allowed to be dispatched. The return value is
+  /// how many cycles until the instruction can be dispatched.
+  /// This method is called after MCA has already checked for
+  /// register and hardware dependencies so this method should only
+  /// implement custom behaviour and dependencies that are not picked up
+  /// by MCA naturally.
+  unsigned checkCustomHazard(ArrayRef<InstRef> IssuedInst,
+                             const InstRef &IR) override;
+};
+} // namespace mca
+} // namespace llvm
+
+#endif