LCOV - code coverage report
Current view: top level - lib/CodeGen - MacroFusion.cpp (source / functions) Hit Total Coverage
Test: llvm-toolchain.info Lines: 46 46 100.0 %
Date: 2018-09-23 13:06:45 Functions: 5 5 100.0 %
Legend: Lines: hit not hit

          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      143220 :   return Dep.getKind() == SDep::Anti || Dep.getKind() == SDep::Output;
      38             : }
      39             : 
      40       35509 : 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       82634 :   for (SDep &SI : FirstSU.Succs)
      45             :     if (SI.isCluster())
      46             :       return false;
      47             : 
      48       95652 :   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       34274 :   if (!DAG.addEdge(&SecondSU, SDep(&FirstSU, SDep::Cluster)))
      58             :     return false;
      59             : 
      60             :   // Adjust the latency between both instrs.
      61      111391 :   for (SDep &SI : FirstSU.Succs)
      62       77117 :     if (SI.getSUnit() == &SecondSU)
      63             :       SI.setLatency(0);
      64             : 
      65      129926 :   for (SDep &SI : SecondSU.Preds)
      66       95652 :     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       34274 :   if (&SecondSU != &DAG.ExitSU)
      78       35189 :     for (const SDep &SI : FirstSU.Succs) {
      79             :       SUnit *SU = SI.getSUnit();
      80       16823 :       if (SI.isWeak() || isHazard(SI) ||
      81       24691 :           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        3281 :       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       34274 :   if (&FirstSU != &DAG.EntrySU) {
      91      129926 :     for (const SDep &SI : SecondSU.Preds) {
      92             :       SUnit *SU = SI.getSUnit();
      93       87600 :       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       26661 :       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       34274 :     if (&SecondSU == &DAG.ExitSU) {
     103      156562 :       for (SUnit &SU : DAG.SUnits) {
     104      131243 :         if (SU.Succs.empty())
     105       17204 :           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      305106 :     : shouldScheduleAdjacent(shouldScheduleAdjacent), FuseBlock(FuseBlock) {}
     126             : 
     127             :   void apply(ScheduleDAGInstrs *DAGInstrs) override;
     128             : };
     129             : 
     130             : } // end anonymous namespace
     131             : 
     132      413432 : void MacroFusion::apply(ScheduleDAGInstrs *DAGInstrs) {
     133             :   ScheduleDAGMI *DAG = static_cast<ScheduleDAGMI*>(DAGInstrs);
     134             : 
     135      413432 :   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      482246 :     for (SUnit &ISU : DAG->SUnits)
     139      439585 :         scheduleAdjacentImpl(*DAG, ISU);
     140             : 
     141      413432 :   if (DAG->ExitSU.getInstr())
     142             :     // Try to fuse the instr in the ExitSU with one in its predecessors.
     143      393782 :     scheduleAdjacentImpl(*DAG, DAG->ExitSU);
     144      413432 : }
     145             : 
     146             : /// Implement the fusion of instr pairs in the scheduling DAG,
     147             : /// anchored at the instr in AnchorSU..
     148      833367 : bool MacroFusion::scheduleAdjacentImpl(ScheduleDAGMI &DAG, SUnit &AnchorSU) {
     149      833367 :   const MachineInstr &AnchorMI = *AnchorSU.getInstr();
     150      833367 :   const TargetInstrInfo &TII = *DAG.TII;
     151      833367 :   const TargetSubtargetInfo &ST = DAG.MF.getSubtarget();
     152             : 
     153             :   // Check if the anchor instr may be fused.
     154      833367 :   if (!shouldScheduleAdjacent(TII, ST, nullptr, AnchorMI))
     155             :     return false;
     156             : 
     157             :   // Explorer for fusion candidates among the dependencies of the anchor instr.
     158       73118 :   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       64332 :     if (DepSU.isBoundaryNode())
     165             :       continue;
     166             : 
     167       64332 :     const MachineInstr *DepMI = DepSU.getInstr();
     168       64332 :     if (!shouldScheduleAdjacent(TII, ST, DepMI, AnchorMI))
     169             :       continue;
     170             : 
     171       35509 :     if (fuseInstructionPair(DAG, DepSU, AnchorSU))
     172             :       return true;
     173             :   }
     174             : 
     175             :   return false;
     176             : }
     177             : 
     178             : std::unique_ptr<ScheduleDAGMutation>
     179       42397 : llvm::createMacroFusionDAGMutation(
     180             :      ShouldSchedulePredTy shouldScheduleAdjacent) {
     181       42397 :   if(EnableMacroFusion)
     182       42397 :     return llvm::make_unique<MacroFusion>(shouldScheduleAdjacent, true);
     183             :   return nullptr;
     184             : }
     185             : 
     186             : std::unique_ptr<ScheduleDAGMutation>
     187      110156 : llvm::createBranchMacroFusionDAGMutation(
     188             :      ShouldSchedulePredTy shouldScheduleAdjacent) {
     189      110156 :   if(EnableMacroFusion)
     190      110156 :     return llvm::make_unique<MacroFusion>(shouldScheduleAdjacent, false);
     191             :   return nullptr;
     192             : }

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