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/CodeGen/Passes.h" 13 #include "llvm/CodeGen/MachineFunctionPass.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/TargetInstrInfo.h" 20 21 namespace { 22 struct PEI : public MachineFunctionPass { 23 const char *getPassName() const { 24 return "Prolog/Epilog Insertion & Frame Finalization"; 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 // Add prolog and epilog code to the function. 45 insertPrologEpilogCode(Fn); 46 47 // Replace all MO_FrameIndex operands with physical register references 48 // and actual offsets. 49 // 50 replaceFrameIndices(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 /// 65 Pass *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 /// 74 void 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 int FrameIdx = FFI->CreateStackObject(RegInfo->getRegClass(RegsToSave[i])); 145 StackSlots.push_back(FrameIdx); 146 } 147 148 // Now that we have a stack slot for each register to be saved, insert spill 149 // code into the entry block... 150 MachineBasicBlock *MBB = Fn.begin(); 151 MachineBasicBlock::iterator I = MBB->begin(); 152 for (unsigned i = 0, e = RegsToSave.size(); i != e; ++i) { 153 const TargetRegisterClass *RC = RegInfo->getRegClass(RegsToSave[i]); 154 155 // Insert the spill to the stack frame... 156 RegInfo->storeRegToStackSlot(*MBB, I, RegsToSave[i], StackSlots[i], RC); 157 } 158 159 // Add code to restore the callee-save registers in each exiting block. 160 const TargetInstrInfo &TII = Fn.getTarget().getInstrInfo(); 161 for (MachineFunction::iterator FI = Fn.begin(), E = Fn.end(); FI != E; ++FI) { 162 // If last instruction is a return instruction, add an epilogue 163 if (TII.isReturn(FI->back()->getOpcode())) { 164 MBB = FI; I = MBB->end()-1; 165 166 for (unsigned i = 0, e = RegsToSave.size(); i != e; ++i) { 167 const TargetRegisterClass *RC = RegInfo->getRegClass(RegsToSave[i]); 168 RegInfo->loadRegFromStackSlot(*MBB, I, RegsToSave[i],StackSlots[i], RC); 169 --I; // Insert in reverse order 170 } 171 } 172 } 173 } 174 175 176 /// calculateFrameObjectOffsets - Calculate actual frame offsets for all of the 177 /// abstract stack objects... 178 /// 179 void PEI::calculateFrameObjectOffsets(MachineFunction &Fn) { 180 const TargetFrameInfo &TFI = Fn.getTarget().getFrameInfo(); 181 182 bool StackGrowsDown = 183 TFI.getStackGrowthDirection() == TargetFrameInfo::StackGrowsDown; 184 assert(StackGrowsDown && "Only tested on stack down growing targets!"); 185 186 // Loop over all of the stack objects, assigning sequential addresses... 187 MachineFrameInfo *FFI = Fn.getFrameInfo(); 188 189 unsigned StackAlignment = TFI.getStackAlignment(); 190 191 // Start at the beginning of the local area... 192 int Offset = TFI.getOffsetOfLocalArea(); 193 for (unsigned i = 0, e = FFI->getObjectIndexEnd(); i != e; ++i) { 194 Offset += FFI->getObjectSize(i); // Allocate Size bytes... 195 196 unsigned Align = FFI->getObjectAlignment(i); 197 assert(Align <= StackAlignment && "Cannot align stack object to higher " 198 "alignment boundary than the stack itself!"); 199 Offset = (Offset+Align-1)/Align*Align; // Adjust to Alignment boundary... 200 201 FFI->setObjectOffset(i, -Offset); // Set the computed offset 202 } 203 204 // Align the final stack pointer offset... 205 Offset = (Offset+StackAlignment-1)/StackAlignment*StackAlignment; 206 207 // Set the final value of the stack pointer... 208 FFI->setStackSize(Offset-TFI.getOffsetOfLocalArea()); 209 } 210 211 212 /// insertPrologEpilogCode - Scan the function for modified caller saved 213 /// registers, insert spill code for these caller saved registers, then add 214 /// prolog and epilog code to the function. 215 /// 216 void PEI::insertPrologEpilogCode(MachineFunction &Fn) { 217 // Add prologue to the function... 218 Fn.getTarget().getRegisterInfo()->emitPrologue(Fn); 219 220 // Add epilogue to restore the callee-save registers in each exiting block 221 const TargetInstrInfo &TII = Fn.getTarget().getInstrInfo(); 222 for (MachineFunction::iterator I = Fn.begin(), E = Fn.end(); I != E; ++I) { 223 // If last instruction is a return instruction, add an epilogue 224 if (TII.isReturn(I->back()->getOpcode())) 225 Fn.getTarget().getRegisterInfo()->emitEpilogue(Fn, *I); 226 } 227 } 228 229 230 /// replaceFrameIndices - Replace all MO_FrameIndex operands with physical 231 /// register references and actual offsets. 232 /// 233 void PEI::replaceFrameIndices(MachineFunction &Fn) { 234 if (!Fn.getFrameInfo()->hasStackObjects()) return; // Nothing to do? 235 236 const TargetMachine &TM = Fn.getTarget(); 237 assert(TM.getRegisterInfo() && "TM::getRegisterInfo() must be implemented!"); 238 const MRegisterInfo &MRI = *TM.getRegisterInfo(); 239 240 for (MachineFunction::iterator BB = Fn.begin(), E = Fn.end(); BB != E; ++BB) 241 for (MachineBasicBlock::iterator I = BB->begin(); I != BB->end(); ++I) 242 for (unsigned i = 0, e = (*I)->getNumOperands(); i != e; ++i) 243 if ((*I)->getOperand(i).isFrameIndex()) { 244 // If this instruction has a FrameIndex operand, we need to use that 245 // target machine register info object to eliminate it. 246 MRI.eliminateFrameIndex(Fn, I); 247 break; 248 } 249 } 250