PrologEpilogInserter.cpp revision 19df3876e6dce016ec4c5ab28320a246ab285001
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 21namespace { 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/// 65FunctionPass *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() && 112 (MO.opIsDefOnly() || MO.opIsDefAndUse())) 113 ModifiedRegs[MO.getReg()] = true; // Register is modified 114 } 115 ++I; 116 } 117 118 MachineFrameInfo *FFI = Fn.getFrameInfo(); 119 FFI->setHasCalls(HasCalls); 120 FFI->setMaxCallFrameSize(MaxCallFrameSize); 121 122 // Now figure out which *callee saved* registers are modified by the current 123 // function, thus needing to be saved and restored in the prolog/epilog. 124 // 125 std::vector<unsigned> RegsToSave; 126 for (unsigned i = 0; CSRegs[i]; ++i) { 127 unsigned Reg = CSRegs[i]; 128 if (ModifiedRegs[Reg]) { 129 RegsToSave.push_back(Reg); // If modified register... 130 } else if (const unsigned *AliasSet = RegInfo->getAliasSet(Reg)) 131 for (unsigned j = 0; AliasSet[j]; ++j) // Check alias registers too... 132 if (ModifiedRegs[AliasSet[j]]) { 133 RegsToSave.push_back(Reg); 134 break; 135 } 136 } 137 138 if (RegsToSave.empty()) 139 return; // Early exit if no caller saved registers are modified! 140 141 // Now that we know which registers need to be saved and restored, allocate 142 // stack slots for them. 143 std::vector<int> StackSlots; 144 for (unsigned i = 0, e = RegsToSave.size(); i != e; ++i) { 145 int FrameIdx = FFI->CreateStackObject(RegInfo->getRegClass(RegsToSave[i])); 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 TargetInstrInfo &TII = 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 (!FI->empty() && TII.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 unsigned StackAlignment = TFI.getStackAlignment(); 191 192 // Start at the beginning of the local area... 193 int Offset = TFI.getOffsetOfLocalArea(); 194 for (unsigned i = 0, e = FFI->getObjectIndexEnd(); i != e; ++i) { 195 Offset += FFI->getObjectSize(i); // Allocate Size bytes... 196 197 unsigned Align = FFI->getObjectAlignment(i); 198 assert(Align <= StackAlignment && "Cannot align stack object to higher " 199 "alignment boundary than the stack itself!"); 200 Offset = (Offset+Align-1)/Align*Align; // Adjust to Alignment boundary... 201 202 FFI->setObjectOffset(i, -Offset); // Set the computed offset 203 } 204 205 // Align the final stack pointer offset... 206 Offset = (Offset+StackAlignment-1)/StackAlignment*StackAlignment; 207 208 // Set the final value of the stack pointer... 209 FFI->setStackSize(Offset-TFI.getOffsetOfLocalArea()); 210} 211 212 213/// insertPrologEpilogCode - Scan the function for modified caller saved 214/// registers, insert spill code for these caller saved registers, then add 215/// prolog and epilog code to the function. 216/// 217void PEI::insertPrologEpilogCode(MachineFunction &Fn) { 218 // Add prologue to the function... 219 Fn.getTarget().getRegisterInfo()->emitPrologue(Fn); 220 221 // Add epilogue to restore the callee-save registers in each exiting block 222 const TargetInstrInfo &TII = Fn.getTarget().getInstrInfo(); 223 for (MachineFunction::iterator I = Fn.begin(), E = Fn.end(); I != E; ++I) { 224 // If last instruction is a return instruction, add an epilogue 225 if (!I->empty() && TII.isReturn(I->back()->getOpcode())) 226 Fn.getTarget().getRegisterInfo()->emitEpilogue(Fn, *I); 227 } 228} 229 230 231/// replaceFrameIndices - Replace all MO_FrameIndex operands with physical 232/// register references and actual offsets. 233/// 234void PEI::replaceFrameIndices(MachineFunction &Fn) { 235 if (!Fn.getFrameInfo()->hasStackObjects()) return; // Nothing to do? 236 237 const TargetMachine &TM = Fn.getTarget(); 238 assert(TM.getRegisterInfo() && "TM::getRegisterInfo() must be implemented!"); 239 const MRegisterInfo &MRI = *TM.getRegisterInfo(); 240 241 for (MachineFunction::iterator BB = Fn.begin(), E = Fn.end(); BB != E; ++BB) 242 for (MachineBasicBlock::iterator I = BB->begin(); I != BB->end(); ++I) 243 for (unsigned i = 0, e = (*I)->getNumOperands(); i != e; ++i) 244 if ((*I)->getOperand(i).isFrameIndex()) { 245 // If this instruction has a FrameIndex operand, we need to use that 246 // target machine register info object to eliminate it. 247 MRI.eliminateFrameIndex(Fn, I); 248 break; 249 } 250} 251