llvm/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) : WorkList(WorkList) {}
  60   virtual ~WorkListMaintainer() = default;
  61
  62   void erasingInstr(MachineInstr &MI) override {
  63     LLVM_DEBUG(dbgs() << "Erasing: " << MI << "\n");
  64     WorkList.remove(&MI);
  65   }
  66   void createdInstr(MachineInstr &MI) override {
  67     LLVM_DEBUG(dbgs() << "Creating: " << MI << "\n");
  68     WorkList.insert(&MI);
  69     LLVM_DEBUG(CreatedInstrs.insert(&MI));
  70   }
  71   void changingInstr(MachineInstr &MI) override {
  72     LLVM_DEBUG(dbgs() << "Changing: " << MI << "\n");
  73     WorkList.insert(&MI);
  74   }
  75   void changedInstr(MachineInstr &MI) override {
  76     LLVM_DEBUG(dbgs() << "Changed: " << MI << "\n");
  77     WorkList.insert(&MI);
  78   }
  79
  80   void reportFullyCreatedInstrs() {
  81     LLVM_DEBUG(for (const auto *MI
  82                     : CreatedInstrs) {
  83       dbgs() << "Created: ";
  84       MI->print(dbgs());
  85     });
  86     LLVM_DEBUG(CreatedInstrs.clear());
  87   }
  88 };
  89 }
  90
  91 Combiner::Combiner(CombinerInfo &Info, const TargetPassConfig *TPC)
  92     : CInfo(Info), TPC(TPC) {
  93   (void)this->TPC; // FIXME: Remove when used.
  94 }
  95
  96 bool Combiner::combineMachineInstrs(MachineFunction &MF,
  97                                     GISelCSEInfo *CSEInfo) {
  98   // If the ISel pipeline failed, do not bother running this pass.
  99   // FIXME: Should this be here or in individual combiner passes.
 100   if (MF.getProperties().hasProperty(
 101           MachineFunctionProperties::Property::FailedISel))
 102     return false;
 103
 104   Builder =
 105       CSEInfo ? std::make_unique<CSEMIRBuilder>() : std::make_unique<MachineIRBuilder>();
 106   MRI = &MF.getRegInfo();
 107   Builder->setMF(MF);
 108   if (CSEInfo)
 109     Builder->setCSEInfo(CSEInfo);
 110
 111   LLVM_DEBUG(dbgs() << "Generic MI Combiner for: " << MF.getName() << '\n');
 112
 113   MachineOptimizationRemarkEmitter MORE(MF, /*MBFI=*/nullptr);
 114
 115   bool MFChanged = false;
 116   bool Changed;
 117   MachineIRBuilder &B = *Builder.get();
 118
 119   do {
 120     // Collect all instructions. Do a post order traversal for basic blocks and
 121     // insert with list bottom up, so while we pop_back_val, we'll traverse top
 122     // down RPOT.
 123     Changed = false;
 124     GISelWorkList<512> WorkList;
 125     WorkListMaintainer Observer(WorkList);
 126     GISelObserverWrapper WrapperObserver(&Observer);
 127     if (CSEInfo)
 128       WrapperObserver.addObserver(CSEInfo);
 129     RAIIDelegateInstaller DelInstall(MF, &WrapperObserver);
 130     for (MachineBasicBlock *MBB : post_order(&MF)) {
 131       for (MachineInstr &CurMI :
 132            llvm::make_early_inc_range(llvm::reverse(*MBB))) {
 133         // Erase dead insts before even adding to the list.
 134         if (isTriviallyDead(CurMI, *MRI)) {
 135           LLVM_DEBUG(dbgs() << CurMI << "Is dead; erasing.\n");
 136           CurMI.eraseFromParent();
 137           continue;
 138         }
 139         WorkList.deferred_insert(&CurMI);
 140       }
 141     }
 142     WorkList.finalize();
 143     // Main Loop. Process the instructions here.
 144     while (!WorkList.empty()) {
 145       MachineInstr *CurrInst = WorkList.pop_back_val();
 146       LLVM_DEBUG(dbgs() << "\nTry combining " << *CurrInst;);
 147       Changed |= CInfo.combine(WrapperObserver, *CurrInst, B);
 148       Observer.reportFullyCreatedInstrs();
 149     }
 150     MFChanged |= Changed;
 151   } while (Changed);
 152
 153 #ifndef NDEBUG
 154   if (CSEInfo) {
 155     if (auto E = CSEInfo->verify()) {
 156       errs() << E << '\n';
 157       assert(false && "CSEInfo is not consistent. Likely missing calls to "
 158                       "observer on mutations.");
 159     }
 160   }
 161 #endif
 162   return MFChanged;
 163 }