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 using namespace llvm; 20 21 #define DEBUG_TYPE "funclet-layout" 22 23 namespace { 24 class FuncletLayout : public MachineFunctionPass { 25 public: 26 static char ID; // Pass identification, replacement for typeid 27 FuncletLayout() : MachineFunctionPass(ID) { 28 initializeFuncletLayoutPass(*PassRegistry::getPassRegistry()); 29 } 30 31 bool runOnMachineFunction(MachineFunction &F) override; 32 }; 33 } 34 35 static void 36 collectFuncletMembers(DenseMap<MachineBasicBlock *, int> &FuncletMembership, 37 int Funclet, MachineBasicBlock *MBB) { 38 // Don't revisit blocks. 39 if (FuncletMembership.count(MBB) > 0) 40 return; 41 42 // Add this MBB to our funclet. 43 FuncletMembership[MBB] = Funclet; 44 45 bool IsReturn = false; 46 int NumTerminators = 0; 47 for (MachineInstr &MI : MBB->terminators()) { 48 IsReturn |= MI.isReturn(); 49 ++NumTerminators; 50 } 51 assert((!IsReturn || NumTerminators == 1) && 52 "Expected only one terminator when a return is present!"); 53 54 // Returns are boundaries where funclet transfer can occur, don't follow 55 // successors. 56 if (IsReturn) 57 return; 58 59 for (MachineBasicBlock *SMBB : MBB->successors()) 60 if (!SMBB->isEHPad()) 61 collectFuncletMembers(FuncletMembership, Funclet, SMBB); 62 } 63 64 char FuncletLayout::ID = 0; 65 char &llvm::FuncletLayoutID = FuncletLayout::ID; 66 INITIALIZE_PASS(FuncletLayout, "funclet-layout", 67 "Contiguously Lay Out Funclets", false, false) 68 69 bool FuncletLayout::runOnMachineFunction(MachineFunction &F) { 70 // We don't have anything to do if there aren't any EH pads. 71 if (!F.getMMI().hasEHFunclets()) 72 return false; 73 74 SmallVector<MachineBasicBlock *, 16> FuncletBlocks; 75 for (MachineBasicBlock &MBB : F) 76 if (MBB.isEHFuncletEntry()) 77 FuncletBlocks.push_back(&MBB); 78 79 // We don't have anything to do if there aren't any EH pads. 80 if (FuncletBlocks.empty()) 81 return false; 82 83 DenseMap<MachineBasicBlock *, int> FuncletMembership; 84 for (MachineBasicBlock *MBB : FuncletBlocks) 85 collectFuncletMembers(FuncletMembership, MBB->getNumber(), MBB); 86 87 F.sort([&](MachineBasicBlock &x, MachineBasicBlock &y) { 88 return FuncletMembership[&x] < FuncletMembership[&y]; 89 }); 90 91 // Conservatively assume we changed something. 92 return true; 93 } 94