PrologEpilogInserter.cpp revision f3e4f0e615bb2c36c4a9d60bb908e08b76025c75
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" 27#include "llvm/Support/Visibility.h" 28using namespace llvm; 29 30namespace { 31 struct VISIBILITY_HIDDEN PEI : public MachineFunctionPass { 32 const char *getPassName() const { 33 return "Prolog/Epilog Insertion & Frame Finalization"; 34 } 35 36 /// runOnMachineFunction - Insert prolog/epilog code and replace abstract 37 /// frame indexes with appropriate references. 38 /// 39 bool runOnMachineFunction(MachineFunction &Fn) { 40 // Get MachineDebugInfo so that we can track the construction of the 41 // frame. 42 if (MachineDebugInfo *DI = getAnalysisToUpdate<MachineDebugInfo>()) { 43 Fn.getFrameInfo()->setMachineDebugInfo(DI); 44 } 45 46 // Scan the function for modified caller saved registers and insert spill 47 // code for any caller saved registers that are modified. Also calculate 48 // the MaxCallFrameSize and HasCalls variables for the function's frame 49 // information and eliminates call frame pseudo instructions. 50 calculateCallerSavedRegisters(Fn); 51 52 // Add the code to save and restore the caller saved registers 53 saveCallerSavedRegisters(Fn); 54 55 // Allow the target machine to make final modifications to the function 56 // before the frame layout is finalized. 57 Fn.getTarget().getRegisterInfo()->processFunctionBeforeFrameFinalized(Fn); 58 59 // Calculate actual frame offsets for all of the abstract stack objects... 60 calculateFrameObjectOffsets(Fn); 61 62 // Add prolog and epilog code to the function. This function is required 63 // to align the stack frame as necessary for any stack variables or 64 // called functions. Because of this, calculateCallerSavedRegisters 65 // must be called before this function in order to set the HasCalls 66 // and MaxCallFrameSize variables. 67 insertPrologEpilogCode(Fn); 68 69 // Replace all MO_FrameIndex operands with physical register references 70 // and actual offsets. 71 // 72 replaceFrameIndices(Fn); 73 74 return true; 75 } 76 77 private: 78 void calculateCallerSavedRegisters(MachineFunction &Fn); 79 void saveCallerSavedRegisters(MachineFunction &Fn); 80 void calculateFrameObjectOffsets(MachineFunction &Fn); 81 void replaceFrameIndices(MachineFunction &Fn); 82 void insertPrologEpilogCode(MachineFunction &Fn); 83 }; 84} 85 86 87/// createPrologEpilogCodeInserter - This function returns a pass that inserts 88/// prolog and epilog code, and eliminates abstract frame references. 89/// 90FunctionPass *llvm::createPrologEpilogCodeInserter() { return new PEI(); } 91 92 93/// calculateCallerSavedRegisters - Scan the function for modified caller saved 94/// registers. Also calculate the MaxCallFrameSize and HasCalls variables for 95/// the function's frame information and eliminates call frame pseudo 96/// instructions. 97/// 98void PEI::calculateCallerSavedRegisters(MachineFunction &Fn) { 99 const MRegisterInfo *RegInfo = Fn.getTarget().getRegisterInfo(); 100 const TargetFrameInfo *TFI = Fn.getTarget().getFrameInfo(); 101 102 // Get the callee saved register list... 103 const unsigned *CSRegs = RegInfo->getCalleeSaveRegs(); 104 105 // Get the function call frame set-up and tear-down instruction opcode 106 int FrameSetupOpcode = RegInfo->getCallFrameSetupOpcode(); 107 int FrameDestroyOpcode = RegInfo->getCallFrameDestroyOpcode(); 108 109 // Early exit for targets which have no callee saved registers and no call 110 // frame setup/destroy pseudo instructions. 111 if ((CSRegs == 0 || CSRegs[0] == 0) && 112 FrameSetupOpcode == -1 && FrameDestroyOpcode == -1) 113 return; 114 115 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 ++I; 130 } 131 132 MachineFrameInfo *FFI = Fn.getFrameInfo(); 133 FFI->setHasCalls(HasCalls); 134 FFI->setMaxCallFrameSize(MaxCallFrameSize); 135 136 // Now figure out which *callee saved* registers are modified by the current 137 // function, thus needing to be saved and restored in the prolog/epilog. 138 // 139 const bool *PhysRegsUsed = Fn.getUsedPhysregs(); 140 const TargetRegisterClass* const *CSRegClasses = 141 RegInfo->getCalleeSaveRegClasses(); 142 std::vector<CalleeSavedInfo> &CSI = FFI->getCalleeSavedInfo(); 143 for (unsigned i = 0; CSRegs[i]; ++i) { 144 unsigned Reg = CSRegs[i]; 145 if (PhysRegsUsed[Reg]) { 146 // If the reg is modified, save it! 147 CSI.push_back(CalleeSavedInfo(Reg, CSRegClasses[i])); 148 } else { 149 for (const unsigned *AliasSet = RegInfo->getAliasSet(Reg); 150 *AliasSet; ++AliasSet) { // Check alias registers too. 151 if (PhysRegsUsed[*AliasSet]) { 152 CSI.push_back(CalleeSavedInfo(Reg, CSRegClasses[i])); 153 break; 154 } 155 } 156 } 157 } 158 159 if (CSI.empty()) 160 return; // Early exit if no caller saved registers are modified! 161 162 unsigned NumFixedSpillSlots; 163 const std::pair<unsigned,int> *FixedSpillSlots = 164 TFI->getCalleeSaveSpillSlots(NumFixedSpillSlots); 165 166 // Now that we know which registers need to be saved and restored, allocate 167 // stack slots for them. 168 for (unsigned i = 0, e = CSI.size(); i != e; ++i) { 169 unsigned Reg = CSI[i].getReg(); 170 const TargetRegisterClass *RC = CSI[i].getRegClass(); 171 172 // Check to see if this physreg must be spilled to a particular stack slot 173 // on this target. 174 const std::pair<unsigned,int> *FixedSlot = FixedSpillSlots; 175 while (FixedSlot != FixedSpillSlots+NumFixedSpillSlots && 176 FixedSlot->first != Reg) 177 ++FixedSlot; 178 179 int FrameIdx; 180 if (FixedSlot == FixedSpillSlots+NumFixedSpillSlots) { 181 // Nope, just spill it anywhere convenient. 182 FrameIdx = FFI->CreateStackObject(RC->getSize(), RC->getAlignment()); 183 } else { 184 // Spill it to the stack where we must. 185 FrameIdx = FFI->CreateFixedObject(RC->getSize(), FixedSlot->second); 186 } 187 CSI[i].setFrameIdx(FrameIdx); 188 } 189} 190 191/// saveCallerSavedRegisters - Insert spill code for any caller saved registers 192/// that are modified in the function. 193/// 194void PEI::saveCallerSavedRegisters(MachineFunction &Fn) { 195 // Get callee saved register information. 196 MachineFrameInfo *FFI = Fn.getFrameInfo(); 197 std::vector<CalleeSavedInfo> &CSI = FFI->getCalleeSavedInfo(); 198 199 // Early exit if no caller saved registers are modified! 200 if (CSI.empty()) 201 return; 202 203 const MRegisterInfo *RegInfo = Fn.getTarget().getRegisterInfo(); 204 205 // Now that we have a stack slot for each register to be saved, insert spill 206 // code into the entry block. 207 MachineBasicBlock *MBB = Fn.begin(); 208 MachineBasicBlock::iterator I = MBB->begin(); 209 for (unsigned i = 0, e = CSI.size(); i != e; ++i) { 210 // Insert the spill to the stack frame. 211 RegInfo->storeRegToStackSlot(*MBB, I, CSI[i].getReg(), CSI[i].getFrameIdx(), 212 CSI[i].getRegClass()); 213 } 214 215 // Add code to restore the callee-save registers in each exiting block. 216 const TargetInstrInfo &TII = *Fn.getTarget().getInstrInfo(); 217 for (MachineFunction::iterator FI = Fn.begin(), E = Fn.end(); FI != E; ++FI) 218 // If last instruction is a return instruction, add an epilogue. 219 if (!FI->empty() && TII.isReturn(FI->back().getOpcode())) { 220 MBB = FI; 221 I = MBB->end(); --I; 222 223 // Skip over all terminator instructions, which are part of the return 224 // sequence. 225 MachineBasicBlock::iterator I2 = I; 226 while (I2 != MBB->begin() && TII.isTerminatorInstr((--I2)->getOpcode())) 227 I = I2; 228 229 bool AtStart = I == MBB->begin(); 230 MachineBasicBlock::iterator BeforeI = I; 231 if (!AtStart) 232 --BeforeI; 233 234 // Restore all registers immediately before the return and any terminators 235 // that preceed it. 236 for (unsigned i = 0, e = CSI.size(); i != e; ++i) { 237 RegInfo->loadRegFromStackSlot(*MBB, I, CSI[i].getReg(), 238 CSI[i].getFrameIdx(), 239 CSI[i].getRegClass()); 240 assert(I != MBB->begin() && 241 "loadRegFromStackSlot didn't insert any code!"); 242 // Insert in reverse order. loadRegFromStackSlot can insert multiple 243 // instructions. 244 if (AtStart) 245 I = MBB->begin(); 246 else { 247 I = BeforeI; 248 ++I; 249 } 250 } 251 } 252} 253 254 255/// calculateFrameObjectOffsets - Calculate actual frame offsets for all of the 256/// abstract stack objects. 257/// 258void PEI::calculateFrameObjectOffsets(MachineFunction &Fn) { 259 const TargetFrameInfo &TFI = *Fn.getTarget().getFrameInfo(); 260 261 bool StackGrowsDown = 262 TFI.getStackGrowthDirection() == TargetFrameInfo::StackGrowsDown; 263 264 // Loop over all of the stack objects, assigning sequential addresses... 265 MachineFrameInfo *FFI = Fn.getFrameInfo(); 266 267 unsigned StackAlignment = TFI.getStackAlignment(); 268 unsigned MaxAlign = 0; 269 270 // Start at the beginning of the local area. 271 // The Offset is the distance from the stack top in the direction 272 // of stack growth -- so it's always positive. 273 int Offset = TFI.getOffsetOfLocalArea(); 274 if (StackGrowsDown) 275 Offset = -Offset; 276 assert(Offset >= 0 277 && "Local area offset should be in direction of stack growth"); 278 279 // If there are fixed sized objects that are preallocated in the local area, 280 // non-fixed objects can't be allocated right at the start of local area. 281 // We currently don't support filling in holes in between fixed sized objects, 282 // so we adjust 'Offset' to point to the end of last fixed sized 283 // preallocated object. 284 for (int i = FFI->getObjectIndexBegin(); i != 0; ++i) { 285 int FixedOff; 286 if (StackGrowsDown) { 287 // The maximum distance from the stack pointer is at lower address of 288 // the object -- which is given by offset. For down growing stack 289 // the offset is negative, so we negate the offset to get the distance. 290 FixedOff = -FFI->getObjectOffset(i); 291 } else { 292 // The maximum distance from the start pointer is at the upper 293 // address of the object. 294 FixedOff = FFI->getObjectOffset(i) + FFI->getObjectSize(i); 295 } 296 if (FixedOff > Offset) Offset = FixedOff; 297 } 298 299 for (unsigned i = 0, e = FFI->getObjectIndexEnd(); i != e; ++i) { 300 // If stack grows down, we need to add size of find the lowest 301 // address of the object. 302 if (StackGrowsDown) 303 Offset += FFI->getObjectSize(i); 304 305 unsigned Align = FFI->getObjectAlignment(i); 306 // If the alignment of this object is greater than that of the stack, then 307 // increase the stack alignment to match. 308 MaxAlign = std::max(MaxAlign, Align); 309 // Adjust to alignment boundary 310 Offset = (Offset+Align-1)/Align*Align; 311 312 if (StackGrowsDown) { 313 FFI->setObjectOffset(i, -Offset); // Set the computed offset 314 } else { 315 FFI->setObjectOffset(i, Offset); 316 Offset += FFI->getObjectSize(i); 317 } 318 } 319 320 // Align the final stack pointer offset, but only if there are calls in the 321 // function. This ensures that any calls to subroutines have their stack 322 // frames suitable aligned. 323 if (FFI->hasCalls()) 324 Offset = (Offset+StackAlignment-1)/StackAlignment*StackAlignment; 325 326 // Set the final value of the stack pointer... 327 FFI->setStackSize(Offset+TFI.getOffsetOfLocalArea()); 328 329 // Remember the required stack alignment in case targets need it to perform 330 // dynamic stack alignment. 331 assert(FFI->getMaxAlignment() == MaxAlign && 332 "Stack alignment calculation broken!"); 333} 334 335 336/// insertPrologEpilogCode - Scan the function for modified caller saved 337/// registers, insert spill code for these caller saved registers, then add 338/// prolog and epilog code to the function. 339/// 340void PEI::insertPrologEpilogCode(MachineFunction &Fn) { 341 // Add prologue to the function... 342 Fn.getTarget().getRegisterInfo()->emitPrologue(Fn); 343 344 // Add epilogue to restore the callee-save registers in each exiting block 345 const TargetInstrInfo &TII = *Fn.getTarget().getInstrInfo(); 346 for (MachineFunction::iterator I = Fn.begin(), E = Fn.end(); I != E; ++I) { 347 // If last instruction is a return instruction, add an epilogue 348 if (!I->empty() && TII.isReturn(I->back().getOpcode())) 349 Fn.getTarget().getRegisterInfo()->emitEpilogue(Fn, *I); 350 } 351} 352 353 354/// replaceFrameIndices - Replace all MO_FrameIndex operands with physical 355/// register references and actual offsets. 356/// 357void PEI::replaceFrameIndices(MachineFunction &Fn) { 358 if (!Fn.getFrameInfo()->hasStackObjects()) return; // Nothing to do? 359 360 const TargetMachine &TM = Fn.getTarget(); 361 assert(TM.getRegisterInfo() && "TM::getRegisterInfo() must be implemented!"); 362 const MRegisterInfo &MRI = *TM.getRegisterInfo(); 363 364 for (MachineFunction::iterator BB = Fn.begin(), E = Fn.end(); BB != E; ++BB) 365 for (MachineBasicBlock::iterator I = BB->begin(); I != BB->end(); ++I) 366 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) 367 if (I->getOperand(i).isFrameIndex()) { 368 // If this instruction has a FrameIndex operand, we need to use that 369 // target machine register info object to eliminate it. 370 MRI.eliminateFrameIndex(I); 371 break; 372 } 373} 374