1 //===--- AMDGPUExportClusting.cpp - AMDGPU Export Clustering -------------===//
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 //
9 /// \file This file contains a DAG scheduling mutation to cluster shader
10 /// exports.
11 //
12 //===----------------------------------------------------------------------===//
13
14 #include "AMDGPUExportClustering.h"
15 #include "MCTargetDesc/AMDGPUMCTargetDesc.h"
16 #include "SIInstrInfo.h"
17 #include "llvm/CodeGen/ScheduleDAGInstrs.h"
18
19 using namespace llvm;
20
21 namespace {
22
23 class ExportClustering : public ScheduleDAGMutation {
24 public:
ExportClustering()25 ExportClustering() {}
26 void apply(ScheduleDAGInstrs *DAG) override;
27 };
28
isExport(const SUnit & SU)29 static bool isExport(const SUnit &SU) {
30 return SIInstrInfo::isEXP(*SU.getInstr());
31 }
32
isPositionExport(const SIInstrInfo * TII,SUnit * SU)33 static bool isPositionExport(const SIInstrInfo *TII, SUnit *SU) {
34 const MachineInstr *MI = SU->getInstr();
35 unsigned Imm = TII->getNamedOperand(*MI, AMDGPU::OpName::tgt)->getImm();
36 return Imm >= AMDGPU::Exp::ET_POS0 && Imm <= AMDGPU::Exp::ET_POS_LAST;
37 }
38
sortChain(const SIInstrInfo * TII,SmallVector<SUnit *,8> & Chain,unsigned PosCount)39 static void sortChain(const SIInstrInfo *TII, SmallVector<SUnit *, 8> &Chain,
40 unsigned PosCount) {
41 if (!PosCount || PosCount == Chain.size())
42 return;
43
44 // Position exports should occur as soon as possible in the shader
45 // for optimal performance. This moves position exports before
46 // other exports while preserving the order within different export
47 // types (pos or other).
48 SmallVector<SUnit *, 8> Copy(Chain);
49 unsigned PosIdx = 0;
50 unsigned OtherIdx = PosCount;
51 for (SUnit *SU : Copy) {
52 if (isPositionExport(TII, SU))
53 Chain[PosIdx++] = SU;
54 else
55 Chain[OtherIdx++] = SU;
56 }
57 }
58
buildCluster(ArrayRef<SUnit * > Exports,ScheduleDAGInstrs * DAG)59 static void buildCluster(ArrayRef<SUnit *> Exports, ScheduleDAGInstrs *DAG) {
60 SUnit *ChainHead = Exports.front();
61
62 // Now construct cluster from chain by adding new edges.
63 for (unsigned Idx = 0, End = Exports.size() - 1; Idx < End; ++Idx) {
64 SUnit *SUa = Exports[Idx];
65 SUnit *SUb = Exports[Idx + 1];
66
67 // Copy all dependencies to the head of the chain to avoid any
68 // computation being inserted into the chain.
69 for (const SDep &Pred : SUb->Preds) {
70 SUnit *PredSU = Pred.getSUnit();
71 if (!isExport(*PredSU) && !Pred.isWeak())
72 DAG->addEdge(ChainHead, SDep(PredSU, SDep::Artificial));
73 }
74
75 // New barrier edge ordering exports
76 DAG->addEdge(SUb, SDep(SUa, SDep::Barrier));
77 // Also add cluster edge
78 DAG->addEdge(SUb, SDep(SUa, SDep::Cluster));
79 }
80 }
81
removeExportDependencies(ScheduleDAGInstrs * DAG,SUnit & SU)82 static void removeExportDependencies(ScheduleDAGInstrs *DAG, SUnit &SU) {
83 SmallVector<SDep, 2> ToAdd, ToRemove;
84
85 for (const SDep &Pred : SU.Preds) {
86 SUnit *PredSU = Pred.getSUnit();
87 if (Pred.isBarrier() && isExport(*PredSU)) {
88 ToRemove.push_back(Pred);
89 if (isExport(SU))
90 continue;
91
92 // If we remove a barrier we need to copy dependencies
93 // from the predecessor to maintain order.
94 for (const SDep &ExportPred : PredSU->Preds) {
95 SUnit *ExportPredSU = ExportPred.getSUnit();
96 if (ExportPred.isBarrier() && !isExport(*ExportPredSU))
97 ToAdd.push_back(SDep(ExportPredSU, SDep::Barrier));
98 }
99 }
100 }
101
102 for (SDep Pred : ToRemove)
103 SU.removePred(Pred);
104 for (SDep Pred : ToAdd)
105 DAG->addEdge(&SU, Pred);
106 }
107
apply(ScheduleDAGInstrs * DAG)108 void ExportClustering::apply(ScheduleDAGInstrs *DAG) {
109 const SIInstrInfo *TII = static_cast<const SIInstrInfo *>(DAG->TII);
110
111 SmallVector<SUnit *, 8> Chain;
112
113 // Pass through DAG gathering a list of exports and removing barrier edges
114 // creating dependencies on exports. Freeing exports of successor edges
115 // allows more scheduling freedom, and nothing should be order dependent
116 // on exports. Edges will be added later to order the exports.
117 unsigned PosCount = 0;
118 for (SUnit &SU : DAG->SUnits) {
119 if (!isExport(SU))
120 continue;
121
122 Chain.push_back(&SU);
123 if (isPositionExport(TII, &SU))
124 PosCount++;
125
126 removeExportDependencies(DAG, SU);
127
128 SmallVector<SDep, 4> Succs(SU.Succs);
129 for (SDep Succ : Succs)
130 removeExportDependencies(DAG, *Succ.getSUnit());
131 }
132
133 // Apply clustering if there are multiple exports
134 if (Chain.size() > 1) {
135 sortChain(TII, Chain, PosCount);
136 buildCluster(Chain, DAG);
137 }
138 }
139
140 } // end namespace
141
142 namespace llvm {
143
createAMDGPUExportClusteringDAGMutation()144 std::unique_ptr<ScheduleDAGMutation> createAMDGPUExportClusteringDAGMutation() {
145 return std::make_unique<ExportClustering>();
146 }
147
148 } // end namespace llvm
149