1 //===-- FuncletLayout.cpp - Contiguously lay out funclets -----------------===// 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 implements basic block placement transformations which result in 11 // funclets being contiguous. 12 // 13 //===----------------------------------------------------------------------===// 14 #include "llvm/CodeGen/Passes.h" 15 #include "llvm/CodeGen/MachineBasicBlock.h" 16 #include "llvm/CodeGen/MachineFunction.h" 17 #include "llvm/CodeGen/MachineFunctionPass.h" 18 #include "llvm/CodeGen/MachineModuleInfo.h" 19 #include "llvm/Target/TargetInstrInfo.h" 20 #include "llvm/Target/TargetSubtargetInfo.h" 21 using namespace llvm; 22 23 #define DEBUG_TYPE "funclet-layout" 24 25 namespace { 26 class FuncletLayout : public MachineFunctionPass { 27 public: 28 static char ID; // Pass identification, replacement for typeid 29 FuncletLayout() : MachineFunctionPass(ID) { 30 initializeFuncletLayoutPass(*PassRegistry::getPassRegistry()); 31 } 32 33 bool runOnMachineFunction(MachineFunction &F) override; 34 }; 35 } 36 37 static void 38 collectFuncletMembers(DenseMap<MachineBasicBlock *, int> &FuncletMembership, 39 int Funclet, MachineBasicBlock *MBB) { 40 // Don't revisit blocks. 41 if (FuncletMembership.count(MBB) > 0) { 42 // FIXME: This is a hack, we need to assert this unconditionally. 43 bool IsProbablyUnreachableBlock = 44 MBB->empty() || 45 (MBB->succ_empty() && !MBB->getFirstTerminator()->isReturn() && 46 MBB->size() == 1); 47 48 if (!IsProbablyUnreachableBlock) { 49 if (FuncletMembership[MBB] != Funclet) { 50 assert(false && "MBB is part of two funclets!"); 51 report_fatal_error("MBB is part of two funclets!"); 52 } 53 } 54 return; 55 } 56 57 // Add this MBB to our funclet. 58 FuncletMembership[MBB] = Funclet; 59 60 bool IsReturn = false; 61 int NumTerminators = 0; 62 for (MachineInstr &MI : MBB->terminators()) { 63 IsReturn |= MI.isReturn(); 64 ++NumTerminators; 65 } 66 assert((!IsReturn || NumTerminators == 1) && 67 "Expected only one terminator when a return is present!"); 68 69 // Returns are boundaries where funclet transfer can occur, don't follow 70 // successors. 71 if (IsReturn) 72 return; 73 74 for (MachineBasicBlock *SMBB : MBB->successors()) 75 if (!SMBB->isEHPad()) 76 collectFuncletMembers(FuncletMembership, Funclet, SMBB); 77 } 78 79 char FuncletLayout::ID = 0; 80 char &llvm::FuncletLayoutID = FuncletLayout::ID; 81 INITIALIZE_PASS(FuncletLayout, "funclet-layout", 82 "Contiguously Lay Out Funclets", false, false) 83 84 bool FuncletLayout::runOnMachineFunction(MachineFunction &F) { 85 // We don't have anything to do if there aren't any EH pads. 86 if (!F.getMMI().hasEHFunclets()) 87 return false; 88 89 const TargetInstrInfo *TII = F.getSubtarget().getInstrInfo(); 90 SmallVector<MachineBasicBlock *, 16> FuncletBlocks; 91 SmallVector<std::pair<MachineBasicBlock *, int>, 16> CatchRetSuccessors; 92 for (MachineBasicBlock &MBB : F) { 93 if (MBB.isEHFuncletEntry()) 94 FuncletBlocks.push_back(&MBB); 95 96 MachineBasicBlock::iterator MBBI = MBB.getFirstTerminator(); 97 if (MBBI->getOpcode() != TII->getCatchReturnOpcode()) 98 continue; 99 100 MachineBasicBlock *Successor = MBBI->getOperand(0).getMBB(); 101 MachineBasicBlock *SuccessorColor = MBBI->getOperand(1).getMBB(); 102 CatchRetSuccessors.push_back({Successor, SuccessorColor->getNumber()}); 103 } 104 105 // We don't have anything to do if there aren't any EH pads. 106 if (FuncletBlocks.empty()) 107 return false; 108 109 DenseMap<MachineBasicBlock *, int> FuncletMembership; 110 // Identify all the basic blocks reachable from the function entry. 111 collectFuncletMembers(FuncletMembership, F.front().getNumber(), F.begin()); 112 // Next, identify all the blocks inside the funclets. 113 for (MachineBasicBlock *MBB : FuncletBlocks) 114 collectFuncletMembers(FuncletMembership, MBB->getNumber(), MBB); 115 // Finally, identify all the targets of a catchret. 116 for (std::pair<MachineBasicBlock *, int> CatchRetPair : CatchRetSuccessors) 117 collectFuncletMembers(FuncletMembership, CatchRetPair.second, 118 CatchRetPair.first); 119 120 F.sort([&](MachineBasicBlock &x, MachineBasicBlock &y) { 121 return FuncletMembership[&x] < FuncletMembership[&y]; 122 }); 123 124 // Conservatively assume we changed something. 125 return true; 126 } 127