lib/CodeGen/GlobalISel/Combiner.cpp

   1 //===-- lib/CodeGen/GlobalISel/GICombiner.cpp -----------------------===//
   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 // This file constains common code to combine machine functions at generic
  11 // level.
  12 //===----------------------------------------------------------------------===//
  13
  14 #include "llvm/CodeGen/GlobalISel/Combiner.h"
  15 #include "llvm/CodeGen/GlobalISel/CombinerInfo.h"
  16 #include "llvm/CodeGen/GlobalISel/MachineIRBuilder.h"
  17 #include "llvm/CodeGen/MachineOptimizationRemarkEmitter.h"
  18 #include "llvm/CodeGen/GlobalISel/GISelWorkList.h"
  19 #include "llvm/ADT/PostOrderIterator.h"
  20 #include "llvm/CodeGen/GlobalISel/Utils.h"
  21 #include "llvm/CodeGen/MachineRegisterInfo.h"
  22 #include "llvm/Support/Debug.h"
  23
  24 #define DEBUG_TYPE "gi-combiner"
  25
  26 using namespace llvm;
  27
  28 namespace {
  29 /// This class acts as the glue the joins the CombinerHelper to the overall
  30 /// Combine algorithm. The CombinerHelper is intended to report the
  31 /// modifications it makes to the MIR to the CombinerChangeObserver and the
  32 /// observer subclass will act on these events. In this case, instruction
  33 /// erasure will cancel any future visits to the erased instruction and
  34 /// instruction creation will schedule that instruction for a future visit.
  35 /// Other Combiner implementations may require more complex behaviour from
  36 /// their CombinerChangeObserver subclass.
  37 class WorkListMaintainer : public CombinerChangeObserver {
  38   using WorkListTy = GISelWorkList<512>;
  39   WorkListTy &WorkList;
  40
  41 public:
  42   WorkListMaintainer(WorkListTy &WorkList) : WorkList(WorkList) {}
  43   virtual ~WorkListMaintainer() {}
  44
  45   void erasedInstr(MachineInstr &MI) override {
  46     LLVM_DEBUG(dbgs() << "Erased: "; MI.print(dbgs()); dbgs() << "\n");
  47     WorkList.remove(&MI);
  48   }
  49   void createdInstr(MachineInstr &MI) override {
  50     LLVM_DEBUG(dbgs() << "Created: "; MI.print(dbgs()); dbgs() << "\n");
  51     WorkList.insert(&MI);
  52   }
  53 };
  54 }
  55
  56 Combiner::Combiner(CombinerInfo &Info, const TargetPassConfig *TPC)
  57     : CInfo(Info), TPC(TPC) {
  58   (void)this->TPC; // FIXME: Remove when used.
  59 }
  60
  61 bool Combiner::combineMachineInstrs(MachineFunction &MF) {
  62   // If the ISel pipeline failed, do not bother running this pass.
  63   // FIXME: Should this be here or in individual combiner passes.
  64   if (MF.getProperties().hasProperty(
  65           MachineFunctionProperties::Property::FailedISel))
  66     return false;
  67
  68   MRI = &MF.getRegInfo();
  69   Builder.setMF(MF);
  70
  71   LLVM_DEBUG(dbgs() << "Generic MI Combiner for: " << MF.getName() << '\n');
  72
  73   MachineOptimizationRemarkEmitter MORE(MF, /*MBFI=*/nullptr);
  74
  75   bool MFChanged = false;
  76   bool Changed;
  77
  78   do {
  79     // Collect all instructions. Do a post order traversal for basic blocks and
  80     // insert with list bottom up, so while we pop_back_val, we'll traverse top
  81     // down RPOT.
  82     Changed = false;
  83     GISelWorkList<512> WorkList;
  84     WorkListMaintainer Observer(WorkList);
  85     for (MachineBasicBlock *MBB : post_order(&MF)) {
  86       if (MBB->empty())
  87         continue;
  88       for (auto MII = MBB->rbegin(), MIE = MBB->rend(); MII != MIE;) {
  89         MachineInstr *CurMI = &*MII;
  90         ++MII;
  91         // Erase dead insts before even adding to the list.
  92         if (isTriviallyDead(*CurMI, *MRI)) {
  93           LLVM_DEBUG(dbgs() << *CurMI << "Is dead; erasing.\n");
  94           CurMI->eraseFromParentAndMarkDBGValuesForRemoval();
  95           continue;
  96         }
  97         WorkList.insert(CurMI);
  98       }
  99     }
 100     // Main Loop. Process the instructions here.
 101     while (!WorkList.empty()) {
 102       MachineInstr *CurrInst = WorkList.pop_back_val();
 103       LLVM_DEBUG(dbgs() << "Try combining " << *CurrInst << "\n";);
 104       Changed |= CInfo.combine(Observer, *CurrInst, Builder);
 105     }
 106     MFChanged |= Changed;
 107   } while (Changed);
 108
 109   return MFChanged;
 110 }