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 "Utils/AMDGPUBaseInfo.h"
21#include "llvm/ADT/SmallVector.h"
22#include "llvm/MCA/CustomBehaviour.h"
23#include "llvm/TargetParser/TargetParser.h"
24
25namespace llvm {
26namespace mca {
27
28class AMDGPUInstrPostProcess : public InstrPostProcess {
29 void processWaitCnt(std::unique_ptr<Instruction> &Inst, const MCInst &MCI);
30
31public:
32 AMDGPUInstrPostProcess(const MCSubtargetInfo &STI, const MCInstrInfo &MCII)
33 : InstrPostProcess(STI, MCII) {}
34
35 ~AMDGPUInstrPostProcess() = default;
36
37 void postProcessInstruction(std::unique_ptr<Instruction> &Inst,
38 const MCInst &MCI) override;
39};
40
41struct WaitCntInfo {
42 bool VmCnt = false;
43 bool ExpCnt = false;
44 bool LgkmCnt = false;
45 bool VsCnt = false;
46};
47
48class AMDGPUCustomBehaviour : public CustomBehaviour {
49 /// Whenever MCA would like to dispatch an s_waitcnt instructions,
50 /// we must check all the instruction that are still executing to see if
51 /// they modify the same CNT as we need to wait for. This vector
52 /// gets built in the constructor and contains 1 WaitCntInfo struct
53 /// for each instruction within the SrcManager. Each element
54 /// tells us which CNTs that instruction may interact with.
55 /// We conservatively assume some instructions interact with more
56 /// CNTs than they do in reality, so we will occasionally wait
57 /// longer than necessary, but we shouldn't ever wait for shorter.
58 std::vector<WaitCntInfo> InstrWaitCntInfo;
59
60 /// This method gets called from the constructor and is
61 /// where we setup the InstrWaitCntInfo vector.
62 /// The core logic for determining which CNTs an instruction
63 /// interacts with is taken from SIInsertWaitcnts::updateEventWaitcntAfter().
64 /// Unfortunately, some of the logic from that function is not available to us
65 /// in this scope so we conservatively end up assuming that some
66 /// instructions interact with more CNTs than they do in reality.
67 void generateWaitCntInfo();
68 /// Helper function used in generateWaitCntInfo()
69 bool hasModifiersSet(const std::unique_ptr<Instruction> &Inst,
70 AMDGPU::OpName OpName) const;
71 /// Helper function used in generateWaitCntInfo()
72 bool isGWS(uint16_t Opcode) const;
73 /// Helper function used in generateWaitCntInfo()
74 bool isAlwaysGDS(uint16_t Opcode) const;
75 /// Helper function used in generateWaitCntInfo()
76 bool isVMEM(const MCInstrDesc &MCID);
77 /// This method gets called from checkCustomHazard when mca is attempting to
78 /// dispatch an s_waitcnt instruction (or one of its variants). The method
79 /// looks at each of the instructions that are still executing in the pipeline
80 /// to determine if the waitcnt should force a wait.
81 unsigned handleWaitCnt(ArrayRef<InstRef> IssuedInst, const InstRef &IR);
82 /// Based on the type of s_waitcnt instruction we are looking at, and what its
83 /// operands are, this method will set the values for each of the cnt
84 /// references provided as arguments.
85 void computeWaitCnt(const InstRef &IR, unsigned &Vmcnt, unsigned &Expcnt,
86 unsigned &Lgkmcnt, unsigned &Vscnt);
87
88public:
89 AMDGPUCustomBehaviour(const MCSubtargetInfo &STI,
90 const mca::SourceMgr &SrcMgr, const MCInstrInfo &MCII);
91
92 ~AMDGPUCustomBehaviour() = default;
93 /// This method is used to determine if an instruction
94 /// should be allowed to be dispatched. The return value is
95 /// how many cycles until the instruction can be dispatched.
96 /// This method is called after MCA has already checked for
97 /// register and hardware dependencies so this method should only
98 /// implement custom behaviour and dependencies that are not picked up
99 /// by MCA naturally.
100 unsigned checkCustomHazard(ArrayRef<InstRef> IssuedInst,
101 const InstRef &IR) override;
102};
103} // namespace mca
104} // namespace llvm
105
106#endif
107