PrologEpilogInserter.cpp revision 57f1b67c347b9ba1f8a1cdc3a55362d4f2aa8653
1//===-- PrologEpilogInserter.cpp - Insert Prolog/Epilog code in function --===// 2// 3// The LLVM Compiler Infrastructure 4// 5// This file was developed by the LLVM research group and is distributed under 6// the University of Illinois Open Source License. See LICENSE.TXT for details. 7// 8//===----------------------------------------------------------------------===// 9// 10// This pass is responsible for finalizing the functions frame layout, saving 11// callee saved registers, and for emitting prolog & epilog code for the 12// function. 13// 14// This pass must be run after register allocation. After this pass is 15// executed, it is illegal to construct MO_FrameIndex operands. 16// 17//===----------------------------------------------------------------------===// 18 19#include "llvm/CodeGen/Passes.h" 20#include "llvm/CodeGen/MachineFunctionPass.h" 21#include "llvm/CodeGen/MachineInstr.h" 22#include "llvm/CodeGen/MachineFrameInfo.h" 23#include "llvm/Target/TargetMachine.h" 24#include "llvm/Target/MRegisterInfo.h" 25#include "llvm/Target/TargetFrameInfo.h" 26#include "llvm/Target/TargetInstrInfo.h" 27using namespace llvm; 28 29namespace { 30 struct PEI : public MachineFunctionPass { 31 const char *getPassName() const { 32 return "Prolog/Epilog Insertion & Frame Finalization"; 33 } 34 35 /// runOnMachineFunction - Insert prolog/epilog code and replace abstract 36 /// frame indexes with appropriate references. 37 /// 38 bool runOnMachineFunction(MachineFunction &Fn) { 39 // Scan the function for modified caller saved registers and insert spill 40 // code for any caller saved registers that are modified. Also calculate 41 // the MaxCallFrameSize and HasCalls variables for the function's frame 42 // information and eliminates call frame pseudo instructions. 43 calculateCallerSavedRegisters(Fn); 44 45 // Add the code to save and restore the caller saved registers 46 saveCallerSavedRegisters(Fn); 47 48 // Allow the target machine to make final modifications to the function 49 // before the frame layout is finalized. 50 Fn.getTarget().getRegisterInfo()->processFunctionBeforeFrameFinalized(Fn); 51 52 // Calculate actual frame offsets for all of the abstract stack objects... 53 calculateFrameObjectOffsets(Fn); 54 55 // Add prolog and epilog code to the function. This function is required 56 // to align the stack frame as necessary for any stack variables or 57 // called functions. Because of this, calculateCallerSavedRegisters 58 // must be called before this function in order to set the HasCalls 59 // and MaxCallFrameSize variables. 60 insertPrologEpilogCode(Fn); 61 62 // Replace all MO_FrameIndex operands with physical register references 63 // and actual offsets. 64 // 65 replaceFrameIndices(Fn); 66 67 RegsToSave.clear(); 68 StackSlots.clear(); 69 return true; 70 } 71 72 private: 73 std::vector<unsigned> RegsToSave; 74 std::vector<int> StackSlots; 75 76 void calculateCallerSavedRegisters(MachineFunction &Fn); 77 void saveCallerSavedRegisters(MachineFunction &Fn); 78 void calculateFrameObjectOffsets(MachineFunction &Fn); 79 void replaceFrameIndices(MachineFunction &Fn); 80 void insertPrologEpilogCode(MachineFunction &Fn); 81 }; 82} 83 84 85/// createPrologEpilogCodeInserter - This function returns a pass that inserts 86/// prolog and epilog code, and eliminates abstract frame references. 87/// 88FunctionPass *llvm::createPrologEpilogCodeInserter() { return new PEI(); } 89 90 91/// calculateCallerSavedRegisters - Scan the function for modified caller saved 92/// registers. Also calculate the MaxCallFrameSize and HasCalls variables for 93/// the function's frame information and eliminates call frame pseudo 94/// instructions. 95/// 96void PEI::calculateCallerSavedRegisters(MachineFunction &Fn) { 97 const MRegisterInfo *RegInfo = Fn.getTarget().getRegisterInfo(); 98 const TargetFrameInfo *TFI = Fn.getTarget().getFrameInfo(); 99 100 // Get the callee saved register list... 101 const unsigned *CSRegs = RegInfo->getCalleeSaveRegs(); 102 103 // Get the function call frame set-up and tear-down instruction opcode 104 int FrameSetupOpcode = RegInfo->getCallFrameSetupOpcode(); 105 int FrameDestroyOpcode = RegInfo->getCallFrameDestroyOpcode(); 106 107 // Early exit for targets which have no callee saved registers and no call 108 // frame setup/destroy pseudo instructions. 109 if ((CSRegs == 0 || CSRegs[0] == 0) && 110 FrameSetupOpcode == -1 && FrameDestroyOpcode == -1) 111 return; 112 113 // This bitset contains an entry for each physical register for the target... 114 std::vector<bool> ModifiedRegs(RegInfo->getNumRegs()); 115 unsigned MaxCallFrameSize = 0; 116 bool HasCalls = false; 117 118 for (MachineFunction::iterator BB = Fn.begin(), E = Fn.end(); BB != E; ++BB) 119 for (MachineBasicBlock::iterator I = BB->begin(); I != BB->end(); ) 120 if (I->getOpcode() == FrameSetupOpcode || 121 I->getOpcode() == FrameDestroyOpcode) { 122 assert(I->getNumOperands() == 1 && "Call Frame Setup/Destroy Pseudo" 123 " instructions should have a single immediate argument!"); 124 unsigned Size = I->getOperand(0).getImmedValue(); 125 if (Size > MaxCallFrameSize) MaxCallFrameSize = Size; 126 HasCalls = true; 127 RegInfo->eliminateCallFramePseudoInstr(Fn, *BB, I++); 128 } else { 129 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) { 130 MachineOperand &MO = I->getOperand(i); 131 if (MO.isRegister() && MO.isDef()) { 132 assert(MRegisterInfo::isPhysicalRegister(MO.getReg()) && 133 "Register allocation must be performed!"); 134 ModifiedRegs[MO.getReg()] = true; // Register is modified 135 } 136 } 137 ++I; 138 } 139 140 MachineFrameInfo *FFI = Fn.getFrameInfo(); 141 FFI->setHasCalls(HasCalls); 142 FFI->setMaxCallFrameSize(MaxCallFrameSize); 143 144 // Now figure out which *callee saved* registers are modified by the current 145 // function, thus needing to be saved and restored in the prolog/epilog. 146 // 147 for (unsigned i = 0; CSRegs[i]; ++i) { 148 unsigned Reg = CSRegs[i]; 149 if (ModifiedRegs[Reg]) { 150 RegsToSave.push_back(Reg); // If modified register... 151 } else { 152 for (const unsigned *AliasSet = RegInfo->getAliasSet(Reg); 153 *AliasSet; ++AliasSet) { // Check alias registers too... 154 if (ModifiedRegs[*AliasSet]) { 155 RegsToSave.push_back(Reg); 156 break; 157 } 158 } 159 } 160 } 161 162 if (RegsToSave.empty()) 163 return; // Early exit if no caller saved registers are modified! 164 165 unsigned NumFixedSpillSlots; 166 const std::pair<unsigned,int> *FixedSpillSlots = 167 TFI->getCalleeSaveSpillSlots(NumFixedSpillSlots); 168 169 // Now that we know which registers need to be saved and restored, allocate 170 // stack slots for them. 171 for (unsigned i = 0, e = RegsToSave.size(); i != e; ++i) { 172 unsigned Reg = RegsToSave[i]; 173 int FrameIdx; 174 const TargetRegisterClass *RC = RegInfo->getRegClass(Reg); 175 176 // Check to see if this physreg must be spilled to a particular stack slot 177 // on this target. 178 const std::pair<unsigned,int> *FixedSlot = FixedSpillSlots; 179 while (FixedSlot != FixedSpillSlots+NumFixedSpillSlots && 180 FixedSlot->first != Reg) 181 ++FixedSlot; 182 183 if (FixedSlot == FixedSpillSlots+NumFixedSpillSlots) { 184 // Nope, just spill it anywhere convenient. 185 FrameIdx = FFI->CreateStackObject(RC); 186 } else { 187 // Spill it to the stack where we must. 188 FrameIdx = FFI->CreateFixedObject(RC->getSize(), FixedSlot->second); 189 } 190 StackSlots.push_back(FrameIdx); 191 } 192} 193 194/// saveCallerSavedRegisters - Insert spill code for any caller saved registers 195/// that are modified in the function. 196/// 197void PEI::saveCallerSavedRegisters(MachineFunction &Fn) { 198 // Early exit if no caller saved registers are modified! 199 if (RegsToSave.empty()) 200 return; 201 202 const MRegisterInfo *RegInfo = Fn.getTarget().getRegisterInfo(); 203 204 // Now that we have a stack slot for each register to be saved, insert spill 205 // code into the entry block... 206 MachineBasicBlock *MBB = Fn.begin(); 207 MachineBasicBlock::iterator I = MBB->begin(); 208 for (unsigned i = 0, e = RegsToSave.size(); i != e; ++i) { 209 // Insert the spill to the stack frame. 210 RegInfo->storeRegToStackSlot(*MBB, I, RegsToSave[i], StackSlots[i]); 211 } 212 213 // Add code to restore the callee-save registers in each exiting block. 214 const TargetInstrInfo &TII = *Fn.getTarget().getInstrInfo(); 215 for (MachineFunction::iterator FI = Fn.begin(), E = Fn.end(); FI != E; ++FI) { 216 // If last instruction is a return instruction, add an epilogue 217 if (!FI->empty() && TII.isReturn(FI->back().getOpcode())) { 218 MBB = FI; 219 I = MBB->end(); --I; 220 221 for (unsigned i = 0, e = RegsToSave.size(); i != e; ++i) { 222 RegInfo->loadRegFromStackSlot(*MBB, I, RegsToSave[i],StackSlots[i]); 223 --I; // Insert in reverse order 224 } 225 } 226 } 227} 228 229 230/// calculateFrameObjectOffsets - Calculate actual frame offsets for all of the 231/// abstract stack objects... 232/// 233void PEI::calculateFrameObjectOffsets(MachineFunction &Fn) { 234 const TargetFrameInfo &TFI = *Fn.getTarget().getFrameInfo(); 235 236 bool StackGrowsDown = 237 TFI.getStackGrowthDirection() == TargetFrameInfo::StackGrowsDown; 238 239 // Loop over all of the stack objects, assigning sequential addresses... 240 MachineFrameInfo *FFI = Fn.getFrameInfo(); 241 242 unsigned StackAlignment = TFI.getStackAlignment(); 243 244 // Start at the beginning of the local area. 245 // The Offset is the distance from the stack top in the direction 246 // of stack growth -- so it's always positive. 247 int Offset = TFI.getOffsetOfLocalArea(); 248 if (StackGrowsDown) 249 Offset = -Offset; 250 assert(Offset >= 0 251 && "Local area offset should be in direction of stack growth"); 252 253 // If there are fixed sized objects that are preallocated in the local area, 254 // non-fixed objects can't be allocated right at the start of local area. 255 // We currently don't support filling in holes in between fixed sized objects, 256 // so we adjust 'Offset' to point to the end of last fixed sized 257 // preallocated object. 258 for (int i = FFI->getObjectIndexBegin(); i != 0; ++i) { 259 int FixedOff; 260 if (StackGrowsDown) { 261 // The maximum distance from the stack pointer is at lower address of 262 // the object -- which is given by offset. For down growing stack 263 // the offset is negative, so we negate the offset to get the distance. 264 FixedOff = -FFI->getObjectOffset(i); 265 } else { 266 // The maximum distance from the start pointer is at the upper 267 // address of the object. 268 FixedOff = FFI->getObjectOffset(i) + FFI->getObjectSize(i); 269 } 270 if (FixedOff > Offset) Offset = FixedOff; 271 } 272 273 for (unsigned i = 0, e = FFI->getObjectIndexEnd(); i != e; ++i) { 274 // If stack grows down, we need to add size of find the lowest 275 // address of the object. 276 if (StackGrowsDown) 277 Offset += FFI->getObjectSize(i); 278 279 unsigned Align = FFI->getObjectAlignment(i); 280 assert(Align <= StackAlignment && "Cannot align stack object to higher " 281 "alignment boundary than the stack itself!"); 282 Offset = (Offset+Align-1)/Align*Align; // Adjust to Alignment boundary... 283 284 if (StackGrowsDown) { 285 FFI->setObjectOffset(i, -Offset); // Set the computed offset 286 } else { 287 FFI->setObjectOffset(i, Offset); 288 Offset += FFI->getObjectSize(i); 289 } 290 } 291 292 // Align the final stack pointer offset, but only if there are calls in the 293 // function. This ensures that any calls to subroutines have their stack 294 // frames suitable aligned. 295 if (FFI->hasCalls()) 296 Offset = (Offset+StackAlignment-1)/StackAlignment*StackAlignment; 297 298 // Set the final value of the stack pointer... 299 FFI->setStackSize(Offset+TFI.getOffsetOfLocalArea()); 300} 301 302 303/// insertPrologEpilogCode - Scan the function for modified caller saved 304/// registers, insert spill code for these caller saved registers, then add 305/// prolog and epilog code to the function. 306/// 307void PEI::insertPrologEpilogCode(MachineFunction &Fn) { 308 // Add prologue to the function... 309 Fn.getTarget().getRegisterInfo()->emitPrologue(Fn); 310 311 // Add epilogue to restore the callee-save registers in each exiting block 312 const TargetInstrInfo &TII = *Fn.getTarget().getInstrInfo(); 313 for (MachineFunction::iterator I = Fn.begin(), E = Fn.end(); I != E; ++I) { 314 // If last instruction is a return instruction, add an epilogue 315 if (!I->empty() && TII.isReturn(I->back().getOpcode())) 316 Fn.getTarget().getRegisterInfo()->emitEpilogue(Fn, *I); 317 } 318} 319 320 321/// replaceFrameIndices - Replace all MO_FrameIndex operands with physical 322/// register references and actual offsets. 323/// 324void PEI::replaceFrameIndices(MachineFunction &Fn) { 325 if (!Fn.getFrameInfo()->hasStackObjects()) return; // Nothing to do? 326 327 const TargetMachine &TM = Fn.getTarget(); 328 assert(TM.getRegisterInfo() && "TM::getRegisterInfo() must be implemented!"); 329 const MRegisterInfo &MRI = *TM.getRegisterInfo(); 330 331 for (MachineFunction::iterator BB = Fn.begin(), E = Fn.end(); BB != E; ++BB) 332 for (MachineBasicBlock::iterator I = BB->begin(); I != BB->end(); ++I) 333 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) 334 if (I->getOperand(i).isFrameIndex()) { 335 // If this instruction has a FrameIndex operand, we need to use that 336 // target machine register info object to eliminate it. 337 MRI.eliminateFrameIndex(I); 338 break; 339 } 340} 341