PrologEpilogInserter.cpp revision eb24db9727a7babe863d5afe70c7bda3a460da18
1//===-- PrologEpilogInserter.cpp - Insert Prolog/Epilog code in function --===// 2// 3// This pass is responsible for finalizing the functions frame layout, saving 4// callee saved registers, and for emitting prolog & epilog code for the 5// function. 6// 7// This pass must be run after register allocation. After this pass is 8// executed, it is illegal to construct MO_FrameIndex operands. 9// 10//===----------------------------------------------------------------------===// 11 12#include "llvm/Pass.h" 13#include "llvm/CodeGen/MachineFunction.h" 14#include "llvm/CodeGen/MachineInstr.h" 15#include "llvm/CodeGen/MachineFrameInfo.h" 16#include "llvm/Target/TargetMachine.h" 17#include "llvm/Target/MRegisterInfo.h" 18#include "llvm/Target/TargetFrameInfo.h" 19#include "llvm/Target/MachineInstrInfo.h" 20 21namespace { 22 struct PEI : public FunctionPass { 23 bool runOnFunction(Function &Fn) { 24 return runOnMachineFunction(MachineFunction::get(&Fn)); 25 } 26 27 /// runOnMachineFunction - Insert prolog/epilog code and replace abstract 28 /// frame indexes with appropriate references. 29 /// 30 bool runOnMachineFunction(MachineFunction &Fn) { 31 // Scan the function for modified caller saved registers and insert spill 32 // code for any caller saved registers that are modified. Also calculate 33 // the MaxCallFrameSize and HasCalls variables for the function's frame 34 // information and eliminates call frame pseudo instructions. 35 saveCallerSavedRegisters(Fn); 36 37 // Allow the target machine to make final modifications to the function 38 // before the frame layout is finalized. 39 Fn.getTarget().getRegisterInfo()->processFunctionBeforeFrameFinalized(Fn); 40 41 // Calculate actual frame offsets for all of the abstract stack objects... 42 calculateFrameObjectOffsets(Fn); 43 44 // Replace all MO_FrameIndex operands with physical register references 45 // and actual offsets. 46 // 47 replaceFrameIndices(Fn); 48 49 // Add prolog and epilog code to the function. 50 insertPrologEpilogCode(Fn); 51 return true; 52 } 53 54 private: 55 void saveCallerSavedRegisters(MachineFunction &Fn); 56 void calculateFrameObjectOffsets(MachineFunction &Fn); 57 void replaceFrameIndices(MachineFunction &Fn); 58 void insertPrologEpilogCode(MachineFunction &Fn); 59 }; 60} 61 62/// createPrologEpilogCodeInserter - This function returns a pass that inserts 63/// prolog and epilog code, and eliminates abstract frame references. 64/// 65Pass *createPrologEpilogCodeInserter() { return new PEI(); } 66 67 68/// saveCallerSavedRegisters - Scan the function for modified caller saved 69/// registers and insert spill code for any caller saved registers that are 70/// modified. Also calculate the MaxCallFrameSize and HasCalls variables for 71/// the function's frame information and eliminates call frame pseudo 72/// instructions. 73/// 74void PEI::saveCallerSavedRegisters(MachineFunction &Fn) { 75 const MRegisterInfo *RegInfo = Fn.getTarget().getRegisterInfo(); 76 const TargetFrameInfo &FrameInfo = Fn.getTarget().getFrameInfo(); 77 78 // Get the callee saved register list... 79 const unsigned *CSRegs = RegInfo->getCalleeSaveRegs(); 80 81 // Get the function call frame set-up and tear-down instruction opcode 82 int FrameSetupOpcode = RegInfo->getCallFrameSetupOpcode(); 83 int FrameDestroyOpcode = RegInfo->getCallFrameDestroyOpcode(); 84 85 // Early exit for targets which have no callee saved registers and no call 86 // frame setup/destroy pseudo instructions. 87 if ((CSRegs == 0 || CSRegs[0] == 0) && 88 FrameSetupOpcode == -1 && FrameDestroyOpcode == -1) 89 return; 90 91 // This bitset contains an entry for each physical register for the target... 92 std::vector<bool> ModifiedRegs(MRegisterInfo::FirstVirtualRegister); 93 unsigned MaxCallFrameSize = 0; 94 bool HasCalls = false; 95 96 for (MachineFunction::iterator BB = Fn.begin(), E = Fn.end(); BB != E; ++BB) 97 for (MachineBasicBlock::iterator I = BB->begin(); I != BB->end(); ) 98 if ((*I)->getOpcode() == FrameSetupOpcode || 99 (*I)->getOpcode() == FrameDestroyOpcode) { 100 assert((*I)->getNumOperands() == 1 && "Call Frame Setup/Destroy Pseudo" 101 " instructions should have a single immediate argument!"); 102 unsigned Size = (*I)->getOperand(0).getImmedValue(); 103 if (Size > MaxCallFrameSize) MaxCallFrameSize = Size; 104 HasCalls = true; 105 RegInfo->eliminateCallFramePseudoInstr(Fn, *BB, I); 106 } else { 107 for (unsigned i = 0, e = (*I)->getNumOperands(); i != e; ++i) { 108 MachineOperand &MO = (*I)->getOperand(i); 109 assert(!MO.isVirtualRegister() && 110 "Register allocation must be performed!"); 111 if (MO.isPhysicalRegister() && MO.opIsDef()) 112 ModifiedRegs[MO.getReg()] = true; // Register is modified 113 } 114 ++I; 115 } 116 117 MachineFrameInfo *FFI = Fn.getFrameInfo(); 118 FFI->setHasCalls(HasCalls); 119 FFI->setMaxCallFrameSize(MaxCallFrameSize); 120 121 // Now figure out which *callee saved* registers are modified by the current 122 // function, thus needing to be saved and restored in the prolog/epilog. 123 // 124 std::vector<unsigned> RegsToSave; 125 for (unsigned i = 0; CSRegs[i]; ++i) { 126 unsigned Reg = CSRegs[i]; 127 if (ModifiedRegs[Reg]) { 128 RegsToSave.push_back(Reg); // If modified register... 129 } else if (const unsigned *AliasSet = RegInfo->getAliasSet(Reg)) 130 for (unsigned j = 0; AliasSet[j]; ++j) // Check alias registers too... 131 if (ModifiedRegs[AliasSet[j]]) { 132 RegsToSave.push_back(Reg); 133 break; 134 } 135 } 136 137 if (RegsToSave.empty()) 138 return; // Early exit if no caller saved registers are modified! 139 140 // Now that we know which registers need to be saved and restored, allocate 141 // stack slots for them. 142 std::vector<int> StackSlots; 143 for (unsigned i = 0, e = RegsToSave.size(); i != e; ++i) { 144 const TargetRegisterClass *RC = RegInfo->getRegClass(RegsToSave[i]); 145 int FrameIdx = FFI->CreateStackObject(RC->getSize(), RC->getAlignment()); 146 StackSlots.push_back(FrameIdx); 147 } 148 149 // Now that we have a stack slot for each register to be saved, insert spill 150 // code into the entry block... 151 MachineBasicBlock *MBB = Fn.begin(); 152 MachineBasicBlock::iterator I = MBB->begin(); 153 for (unsigned i = 0, e = RegsToSave.size(); i != e; ++i) { 154 const TargetRegisterClass *RC = RegInfo->getRegClass(RegsToSave[i]); 155 156 // Insert the spill to the stack frame... 157 RegInfo->storeRegToStackSlot(*MBB, I, RegsToSave[i], StackSlots[i], RC); 158 } 159 160 // Add code to restore the callee-save registers in each exiting block. 161 const MachineInstrInfo &MII = Fn.getTarget().getInstrInfo(); 162 for (MachineFunction::iterator FI = Fn.begin(), E = Fn.end(); FI != E; ++FI) { 163 // If last instruction is a return instruction, add an epilogue 164 if (MII.isReturn(FI->back()->getOpcode())) { 165 MBB = FI; I = MBB->end()-1; 166 167 for (unsigned i = 0, e = RegsToSave.size(); i != e; ++i) { 168 const TargetRegisterClass *RC = RegInfo->getRegClass(RegsToSave[i]); 169 RegInfo->loadRegFromStackSlot(*MBB, I, RegsToSave[i],StackSlots[i], RC); 170 --I; // Insert in reverse order 171 } 172 } 173 } 174} 175 176 177/// calculateFrameObjectOffsets - Calculate actual frame offsets for all of the 178/// abstract stack objects... 179/// 180void PEI::calculateFrameObjectOffsets(MachineFunction &Fn) { 181 const TargetFrameInfo &TFI = Fn.getTarget().getFrameInfo(); 182 183 bool StackGrowsDown = 184 TFI.getStackGrowthDirection() == TargetFrameInfo::StackGrowsDown; 185 assert(StackGrowsDown && "Only tested on stack down growing targets!"); 186 187 // Loop over all of the stack objects, assigning sequential addresses... 188 MachineFrameInfo *FFI = Fn.getFrameInfo(); 189 190 // Start at the beginning of the local area... 191 int Offset = -TFI.getOffsetOfLocalArea(); 192 for (unsigned i = 0, e = FFI->getObjectIndexEnd(); i != e; ++i) { 193 Offset += FFI->getObjectSize(i); // Allocate Size bytes... 194 195 unsigned Align = FFI->getObjectAlignment(i); 196 Offset = (Offset+Align-1)/Align*Align; // Adjust to Alignment boundary... 197 198 FFI->setObjectOffset(i, -Offset); // Set the computed offset 199 } 200 201 // Align the final stack pointer offset... 202 unsigned StackAlign = TFI.getStackAlignment(); 203 Offset = (Offset+StackAlign-1)/StackAlign*StackAlign; 204 205 // Set the final value of the stack pointer... 206 FFI->setStackSize(Offset); 207} 208 209 210/// replaceFrameIndices - Replace all MO_FrameIndex operands with physical 211/// register references and actual offsets. 212/// 213void PEI::replaceFrameIndices(MachineFunction &Fn) { 214 if (!Fn.getFrameInfo()->hasStackObjects()) return; // Nothing to do? 215 216 const TargetMachine &TM = Fn.getTarget(); 217 assert(TM.getRegisterInfo() && "TM::getRegisterInfo() must be implemented!"); 218 const MRegisterInfo &MRI = *TM.getRegisterInfo(); 219 220 for (MachineFunction::iterator BB = Fn.begin(), E = Fn.end(); BB != E; ++BB) 221 for (MachineBasicBlock::iterator I = BB->begin(); I != BB->end(); ++I) 222 for (unsigned i = 0, e = (*I)->getNumOperands(); i != e; ++i) 223 if ((*I)->getOperand(i).isFrameIndex()) { 224 // If this instruction has a FrameIndex operand, we need to use that 225 // target machine register info object to eliminate it. 226 MRI.eliminateFrameIndex(Fn, I); 227 break; 228 } 229} 230 231 232/// insertPrologEpilogCode - Scan the function for modified caller saved 233/// registers, insert spill code for these caller saved registers, then add 234/// prolog and epilog code to the function. 235/// 236void PEI::insertPrologEpilogCode(MachineFunction &Fn) { 237 // Add prologue to the function... 238 Fn.getTarget().getRegisterInfo()->emitPrologue(Fn); 239 240 // Add epilogue to restore the callee-save registers in each exiting block 241 const MachineInstrInfo &MII = Fn.getTarget().getInstrInfo(); 242 for (MachineFunction::iterator I = Fn.begin(), E = Fn.end(); I != E; ++I) { 243 // If last instruction is a return instruction, add an epilogue 244 if (MII.isReturn(I->back()->getOpcode())) 245 Fn.getTarget().getRegisterInfo()->emitEpilogue(Fn, *I); 246 } 247} 248