lib/CodeGen/GlobalISel/Combiner.cpp

   1 //===-- lib/CodeGen/GlobalISel/Combiner.cpp -------------------------------===//
   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 // This file constains common code to combine machine functions at generic
  10 // level.
  11 //===----------------------------------------------------------------------===//
  12
  13 #include "llvm/CodeGen/GlobalISel/Combiner.h"
  14 #include "llvm/ADT/PostOrderIterator.h"
  15 #include "llvm/CodeGen/GlobalISel/CSEInfo.h"
  16 #include "llvm/CodeGen/GlobalISel/CombinerInfo.h"
  17 #include "llvm/CodeGen/GlobalISel/CSEMIRBuilder.h"
  18 #include "llvm/CodeGen/GlobalISel/GISelChangeObserver.h"
  19 #include "llvm/CodeGen/GlobalISel/GISelWorkList.h"
  20 #include "llvm/CodeGen/GlobalISel/MachineIRBuilder.h"
  21 #include "llvm/CodeGen/GlobalISel/Utils.h"
  22 #include "llvm/CodeGen/MachineOptimizationRemarkEmitter.h"
  23 #include "llvm/CodeGen/MachineRegisterInfo.h"
  24 #include "llvm/Support/Debug.h"
  25
  26 #define DEBUG_TYPE "gi-combiner"
  27
  28 using namespace llvm;
  29
  30 namespace llvm {
  31 cl::OptionCategory GICombinerOptionCategory(
  32     "GlobalISel Combiner",
  33     "Control the rules which are enabled. These options all take a comma "
  34     "separated list of rules to disable and may be specified by number "
  35     "or number range (e.g. 1-10)."
  36 #ifndef NDEBUG
  37     " They may also be specified by name."
  38 #endif
  39 );
  40 } // end namespace llvm
  41
  42 namespace {
  43 /// This class acts as the glue the joins the CombinerHelper to the overall
  44 /// Combine algorithm. The CombinerHelper is intended to report the
  45 /// modifications it makes to the MIR to the GISelChangeObserver and the
  46 /// observer subclass will act on these events. In this case, instruction
  47 /// erasure will cancel any future visits to the erased instruction and
  48 /// instruction creation will schedule that instruction for a future visit.
  49 /// Other Combiner implementations may require more complex behaviour from
  50 /// their GISelChangeObserver subclass.
  51 class WorkListMaintainer : public GISelChangeObserver {
  52   using WorkListTy = GISelWorkList<512>;
  53   WorkListTy &WorkList;
  54   /// The instructions that have been created but we want to report once they
  55   /// have their operands. This is only maintained if debug output is requested.
  56   SmallPtrSet<const MachineInstr *, 4> CreatedInstrs;
  57
  58 public:
  59   WorkListMaintainer(WorkListTy &WorkList)
  60       : GISelChangeObserver(), WorkList(WorkList) {}
  61   virtual ~WorkListMaintainer() {
  62   }
  63
  64   void erasingInstr(MachineInstr &MI) override {
  65     LLVM_DEBUG(dbgs() << "Erasing: " << MI << "\n");
  66     WorkList.remove(&MI);
  67   }
  68   void createdInstr(MachineInstr &MI) override {
  69     LLVM_DEBUG(dbgs() << "Creating: " << MI << "\n");
  70     WorkList.insert(&MI);
  71     LLVM_DEBUG(CreatedInstrs.insert(&MI));
  72   }
  73   void changingInstr(MachineInstr &MI) override {
  74     LLVM_DEBUG(dbgs() << "Changing: " << MI << "\n");
  75     WorkList.insert(&MI);
  76   }
  77   void changedInstr(MachineInstr &MI) override {
  78     LLVM_DEBUG(dbgs() << "Changed: " << MI << "\n");
  79     WorkList.insert(&MI);
  80   }
  81
  82   void reportFullyCreatedInstrs() {
  83     LLVM_DEBUG(for (const auto *MI
  84                     : CreatedInstrs) {
  85       dbgs() << "Created: ";
  86       MI->print(dbgs());
  87     });
  88     LLVM_DEBUG(CreatedInstrs.clear());
  89   }
  90 };
  91 }
  92
  93 Combiner::Combiner(CombinerInfo &Info, const TargetPassConfig *TPC)
  94     : CInfo(Info), TPC(TPC) {
  95   (void)this->TPC; // FIXME: Remove when used.
  96 }
  97
  98 bool Combiner::combineMachineInstrs(MachineFunction &MF,
  99                                     GISelCSEInfo *CSEInfo) {
 100   // If the ISel pipeline failed, do not bother running this pass.
 101   // FIXME: Should this be here or in individual combiner passes.
 102   if (MF.getProperties().hasProperty(
 103           MachineFunctionProperties::Property::FailedISel))
 104     return false;
 105
 106   Builder =
 107       CSEInfo ? std::make_unique<CSEMIRBuilder>() : std::make_unique<MachineIRBuilder>();
 108   MRI = &MF.getRegInfo();
 109   Builder->setMF(MF);
 110   if (CSEInfo)
 111     Builder->setCSEInfo(CSEInfo);
 112
 113   LLVM_DEBUG(dbgs() << "Generic MI Combiner for: " << MF.getName() << '\n');
 114
 115   MachineOptimizationRemarkEmitter MORE(MF, /*MBFI=*/nullptr);
 116
 117   bool MFChanged = false;
 118   bool Changed;
 119   MachineIRBuilder &B = *Builder.get();
 120
 121   do {
 122     // Collect all instructions. Do a post order traversal for basic blocks and
 123     // insert with list bottom up, so while we pop_back_val, we'll traverse top
 124     // down RPOT.
 125     Changed = false;
 126     GISelWorkList<512> WorkList;
 127     WorkListMaintainer Observer(WorkList);
 128     GISelObserverWrapper WrapperObserver(&Observer);
 129     if (CSEInfo)
 130       WrapperObserver.addObserver(CSEInfo);
 131     RAIIDelegateInstaller DelInstall(MF, &WrapperObserver);
 132     for (MachineBasicBlock *MBB : post_order(&MF)) {
 133       if (MBB->empty())
 134         continue;
 135       for (auto MII = MBB->rbegin(), MIE = MBB->rend(); MII != MIE;) {
 136         MachineInstr *CurMI = &*MII;
 137         ++MII;
 138         // Erase dead insts before even adding to the list.
 139         if (isTriviallyDead(*CurMI, *MRI)) {
 140           LLVM_DEBUG(dbgs() << *CurMI << "Is dead; erasing.\n");
 141           CurMI->eraseFromParentAndMarkDBGValuesForRemoval();
 142           continue;
 143         }
 144         WorkList.deferred_insert(CurMI);
 145       }
 146     }
 147     WorkList.finalize();
 148     // Main Loop. Process the instructions here.
 149     while (!WorkList.empty()) {
 150       MachineInstr *CurrInst = WorkList.pop_back_val();
 151       LLVM_DEBUG(dbgs() << "\nTry combining " << *CurrInst;);
 152       Changed |= CInfo.combine(WrapperObserver, *CurrInst, B);
 153       Observer.reportFullyCreatedInstrs();
 154     }
 155     MFChanged |= Changed;
 156   } while (Changed);
 157
 158   return MFChanged;
 159 }