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