Line data Source code
1 : //===- MacroFusion.cpp - Macro Fusion -------------------------------------===//
2 : //
3 : // The LLVM Compiler Infrastructure
4 : //
5 : // This file is distributed under the University of Illinois Open Source
6 : // License. See LICENSE.TXT for details.
7 : //
8 : //===----------------------------------------------------------------------===//
9 : //
10 : /// \file This file contains the implementation of the DAG scheduling mutation
11 : /// to pair instructions back to back.
12 : //
13 : //===----------------------------------------------------------------------===//
14 :
15 : #include "llvm/CodeGen/MacroFusion.h"
16 : #include "llvm/ADT/STLExtras.h"
17 : #include "llvm/ADT/Statistic.h"
18 : #include "llvm/CodeGen/MachineInstr.h"
19 : #include "llvm/CodeGen/MachineScheduler.h"
20 : #include "llvm/CodeGen/ScheduleDAG.h"
21 : #include "llvm/CodeGen/ScheduleDAGMutation.h"
22 : #include "llvm/CodeGen/TargetInstrInfo.h"
23 : #include "llvm/Support/CommandLine.h"
24 : #include "llvm/Support/Debug.h"
25 : #include "llvm/Support/raw_ostream.h"
26 :
27 : #define DEBUG_TYPE "machine-scheduler"
28 :
29 : STATISTIC(NumFused, "Number of instr pairs fused");
30 :
31 : using namespace llvm;
32 :
33 : static cl::opt<bool> EnableMacroFusion("misched-fusion", cl::Hidden,
34 : cl::desc("Enable scheduling for macro fusion."), cl::init(true));
35 :
36 : static bool isHazard(const SDep &Dep) {
37 144380 : return Dep.getKind() == SDep::Anti || Dep.getKind() == SDep::Output;
38 : }
39 :
40 35782 : static bool fuseInstructionPair(ScheduleDAGMI &DAG, SUnit &FirstSU,
41 : SUnit &SecondSU) {
42 : // Check that neither instr is already paired with another along the edge
43 : // between them.
44 83308 : for (SDep &SI : FirstSU.Succs)
45 : if (SI.isCluster())
46 : return false;
47 :
48 96561 : for (SDep &SI : SecondSU.Preds)
49 : if (SI.isCluster())
50 : return false;
51 : // Though the reachability checks above could be made more generic,
52 : // perhaps as part of ScheduleDAGMI::addEdge(), since such edges are valid,
53 : // the extra computation cost makes it less interesting in general cases.
54 :
55 : // Create a single weak edge between the adjacent instrs. The only effect is
56 : // to cause bottom-up scheduling to heavily prioritize the clustered instrs.
57 34539 : if (!DAG.addEdge(&SecondSU, SDep(&FirstSU, SDep::Cluster)))
58 : return false;
59 :
60 : // Adjust the latency between both instrs.
61 112286 : for (SDep &SI : FirstSU.Succs)
62 77747 : if (SI.getSUnit() == &SecondSU)
63 : SI.setLatency(0);
64 :
65 131100 : for (SDep &SI : SecondSU.Preds)
66 96561 : if (SI.getSUnit() == &FirstSU)
67 : SI.setLatency(0);
68 :
69 : LLVM_DEBUG(
70 : dbgs() << "Macro fuse: "; DAG.dumpNodeName(FirstSU); dbgs() << " - ";
71 : DAG.dumpNodeName(SecondSU); dbgs() << " / ";
72 : dbgs() << DAG.TII->getName(FirstSU.getInstr()->getOpcode()) << " - "
73 : << DAG.TII->getName(SecondSU.getInstr()->getOpcode()) << '\n';);
74 :
75 : // Make data dependencies from the FirstSU also dependent on the SecondSU to
76 : // prevent them from being scheduled between the FirstSU and the SecondSU.
77 34539 : if (&SecondSU != &DAG.ExitSU)
78 35495 : for (const SDep &SI : FirstSU.Succs) {
79 : SUnit *SU = SI.getSUnit();
80 16990 : if (SI.isWeak() || isHazard(SI) ||
81 24956 : SU == &DAG.ExitSU || SU == &SecondSU || SU->isPred(&SecondSU))
82 : continue;
83 : LLVM_DEBUG(dbgs() << " Bind "; DAG.dumpNodeName(SecondSU);
84 : dbgs() << " - "; DAG.dumpNodeName(*SU); dbgs() << '\n';);
85 3355 : DAG.addEdge(SU, SDep(&SecondSU, SDep::Artificial));
86 : }
87 :
88 : // Make the FirstSU also dependent on the dependencies of the SecondSU to
89 : // prevent them from being scheduled between the FirstSU and the SecondSU.
90 34539 : if (&FirstSU != &DAG.EntrySU) {
91 131100 : for (const SDep &SI : SecondSU.Preds) {
92 : SUnit *SU = SI.getSUnit();
93 88621 : if (SI.isWeak() || isHazard(SI) || &FirstSU == SU || FirstSU.isSucc(SU))
94 : continue;
95 : LLVM_DEBUG(dbgs() << " Bind "; DAG.dumpNodeName(*SU); dbgs() << " - ";
96 : DAG.dumpNodeName(FirstSU); dbgs() << '\n';);
97 27039 : DAG.addEdge(&FirstSU, SDep(SU, SDep::Artificial));
98 : }
99 : // ExitSU comes last by design, which acts like an implicit dependency
100 : // between ExitSU and any bottom root in the graph. We should transfer
101 : // this to FirstSU as well.
102 34539 : if (&SecondSU == &DAG.ExitSU) {
103 157397 : for (SUnit &SU : DAG.SUnits) {
104 131882 : if (SU.Succs.empty())
105 17200 : DAG.addEdge(&FirstSU, SDep(&SU, SDep::Artificial));
106 : }
107 : }
108 : }
109 :
110 : ++NumFused;
111 : return true;
112 : }
113 :
114 : namespace {
115 :
116 : /// Post-process the DAG to create cluster edges between instrs that may
117 : /// be fused by the processor into a single operation.
118 : class MacroFusion : public ScheduleDAGMutation {
119 : ShouldSchedulePredTy shouldScheduleAdjacent;
120 : bool FuseBlock;
121 : bool scheduleAdjacentImpl(ScheduleDAGMI &DAG, SUnit &AnchorSU);
122 :
123 : public:
124 : MacroFusion(ShouldSchedulePredTy shouldScheduleAdjacent, bool FuseBlock)
125 309418 : : shouldScheduleAdjacent(shouldScheduleAdjacent), FuseBlock(FuseBlock) {}
126 :
127 : void apply(ScheduleDAGInstrs *DAGInstrs) override;
128 : };
129 :
130 : } // end anonymous namespace
131 :
132 411247 : void MacroFusion::apply(ScheduleDAGInstrs *DAGInstrs) {
133 : ScheduleDAGMI *DAG = static_cast<ScheduleDAGMI*>(DAGInstrs);
134 :
135 411247 : if (FuseBlock)
136 : // For each of the SUnits in the scheduling block, try to fuse the instr in
137 : // it with one in its predecessors.
138 494262 : for (SUnit &ISU : DAG->SUnits)
139 450705 : scheduleAdjacentImpl(*DAG, ISU);
140 :
141 411247 : if (DAG->ExitSU.getInstr())
142 : // Try to fuse the instr in the ExitSU with one in its predecessors.
143 391639 : scheduleAdjacentImpl(*DAG, DAG->ExitSU);
144 411247 : }
145 :
146 : /// Implement the fusion of instr pairs in the scheduling DAG,
147 : /// anchored at the instr in AnchorSU..
148 842344 : bool MacroFusion::scheduleAdjacentImpl(ScheduleDAGMI &DAG, SUnit &AnchorSU) {
149 842344 : const MachineInstr &AnchorMI = *AnchorSU.getInstr();
150 842344 : const TargetInstrInfo &TII = *DAG.TII;
151 842344 : const TargetSubtargetInfo &ST = DAG.MF.getSubtarget();
152 :
153 : // Check if the anchor instr may be fused.
154 842344 : if (!shouldScheduleAdjacent(TII, ST, nullptr, AnchorMI))
155 : return false;
156 :
157 : // Explorer for fusion candidates among the dependencies of the anchor instr.
158 73496 : for (SDep &Dep : AnchorSU.Preds) {
159 : // Ignore dependencies other than data or strong ordering.
160 : if (Dep.isWeak() || isHazard(Dep))
161 : continue;
162 :
163 : SUnit &DepSU = *Dep.getSUnit();
164 64680 : if (DepSU.isBoundaryNode())
165 : continue;
166 :
167 64680 : const MachineInstr *DepMI = DepSU.getInstr();
168 64680 : if (!shouldScheduleAdjacent(TII, ST, DepMI, AnchorMI))
169 : continue;
170 :
171 35782 : if (fuseInstructionPair(DAG, DepSU, AnchorSU))
172 : return true;
173 : }
174 :
175 : return false;
176 : }
177 :
178 : std::unique_ptr<ScheduleDAGMutation>
179 43250 : llvm::createMacroFusionDAGMutation(
180 : ShouldSchedulePredTy shouldScheduleAdjacent) {
181 43250 : if(EnableMacroFusion)
182 43250 : return llvm::make_unique<MacroFusion>(shouldScheduleAdjacent, true);
183 : return nullptr;
184 : }
185 :
186 : std::unique_ptr<ScheduleDAGMutation>
187 111459 : llvm::createBranchMacroFusionDAGMutation(
188 : ShouldSchedulePredTy shouldScheduleAdjacent) {
189 111459 : if(EnableMacroFusion)
190 111459 : return llvm::make_unique<MacroFusion>(shouldScheduleAdjacent, false);
191 : return nullptr;
192 : }
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