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