PrologEpilogInserter.cpp revision c2b4ec37dea2586765a04d74120e1b6197bbd804
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/Compiler.h" 28#include <climits> 29using namespace llvm; 30 31namespace { 32 struct VISIBILITY_HIDDEN PEI : public MachineFunctionPass { 33 const char *getPassName() const { 34 return "Prolog/Epilog Insertion & Frame Finalization"; 35 } 36 37 /// runOnMachineFunction - Insert prolog/epilog code and replace abstract 38 /// frame indexes with appropriate references. 39 /// 40 bool runOnMachineFunction(MachineFunction &Fn) { 41 // Get MachineDebugInfo so that we can track the construction of the 42 // frame. 43 if (MachineDebugInfo *DI = getAnalysisToUpdate<MachineDebugInfo>()) { 44 Fn.getFrameInfo()->setMachineDebugInfo(DI); 45 } 46 47 // Allow the target machine to make some adjustments to the function 48 // e.g. UsedPhysRegs before calculateCalleeSavedRegisters. 49 Fn.getTarget().getRegisterInfo()->processFunctionBeforeCalleeSaveScan(Fn); 50 51 // Scan the function for modified callee saved registers and insert spill 52 // code for any callee saved registers that are modified. Also calculate 53 // the MaxCallFrameSize and HasCalls variables for the function's frame 54 // information and eliminates call frame pseudo instructions. 55 calculateCalleeSavedRegisters(Fn); 56 57 // Add the code to save and restore the callee saved registers 58 saveCalleeSavedRegisters(Fn); 59 60 // Allow the target machine to make final modifications to the function 61 // before the frame layout is finalized. 62 Fn.getTarget().getRegisterInfo()->processFunctionBeforeFrameFinalized(Fn); 63 64 // Calculate actual frame offsets for all of the abstract stack objects... 65 calculateFrameObjectOffsets(Fn); 66 67 // Add prolog and epilog code to the function. This function is required 68 // to align the stack frame as necessary for any stack variables or 69 // called functions. Because of this, calculateCalleeSavedRegisters 70 // must be called before this function in order to set the HasCalls 71 // and MaxCallFrameSize variables. 72 insertPrologEpilogCode(Fn); 73 74 // Replace all MO_FrameIndex operands with physical register references 75 // and actual offsets. 76 // 77 replaceFrameIndices(Fn); 78 79 return true; 80 } 81 82 private: 83 // MinCSFrameIndex, MaxCSFrameIndex - Keeps the range of callee save 84 // stack frame indexes. 85 unsigned MinCSFrameIndex, MaxCSFrameIndex; 86 87 void calculateCalleeSavedRegisters(MachineFunction &Fn); 88 void saveCalleeSavedRegisters(MachineFunction &Fn); 89 void calculateFrameObjectOffsets(MachineFunction &Fn); 90 void replaceFrameIndices(MachineFunction &Fn); 91 void insertPrologEpilogCode(MachineFunction &Fn); 92 }; 93} 94 95 96/// createPrologEpilogCodeInserter - This function returns a pass that inserts 97/// prolog and epilog code, and eliminates abstract frame references. 98/// 99FunctionPass *llvm::createPrologEpilogCodeInserter() { return new PEI(); } 100 101 102/// calculateCalleeSavedRegisters - Scan the function for modified callee saved 103/// registers. Also calculate the MaxCallFrameSize and HasCalls variables for 104/// the function's frame information and eliminates call frame pseudo 105/// instructions. 106/// 107void PEI::calculateCalleeSavedRegisters(MachineFunction &Fn) { 108 const MRegisterInfo *RegInfo = Fn.getTarget().getRegisterInfo(); 109 const TargetFrameInfo *TFI = Fn.getTarget().getFrameInfo(); 110 111 // Get the callee saved register list... 112 const unsigned *CSRegs = RegInfo->getCalleeSaveRegs(); 113 114 // Get the function call frame set-up and tear-down instruction opcode 115 int FrameSetupOpcode = RegInfo->getCallFrameSetupOpcode(); 116 int FrameDestroyOpcode = RegInfo->getCallFrameDestroyOpcode(); 117 118 // Early exit for targets which have no callee saved registers and no call 119 // frame setup/destroy pseudo instructions. 120 if ((CSRegs == 0 || CSRegs[0] == 0) && 121 FrameSetupOpcode == -1 && FrameDestroyOpcode == -1) 122 return; 123 124 unsigned MaxCallFrameSize = 0; 125 bool HasCalls = false; 126 127 for (MachineFunction::iterator BB = Fn.begin(), E = Fn.end(); BB != E; ++BB) 128 for (MachineBasicBlock::iterator I = BB->begin(); I != BB->end(); ) 129 if (I->getOpcode() == FrameSetupOpcode || 130 I->getOpcode() == FrameDestroyOpcode) { 131 assert(I->getNumOperands() >= 1 && "Call Frame Setup/Destroy Pseudo" 132 " instructions should have a single immediate argument!"); 133 unsigned Size = I->getOperand(0).getImmedValue(); 134 if (Size > MaxCallFrameSize) MaxCallFrameSize = Size; 135 HasCalls = true; 136 RegInfo->eliminateCallFramePseudoInstr(Fn, *BB, I++); 137 } else { 138 ++I; 139 } 140 141 MachineFrameInfo *FFI = Fn.getFrameInfo(); 142 FFI->setHasCalls(HasCalls); 143 FFI->setMaxCallFrameSize(MaxCallFrameSize); 144 145 // Now figure out which *callee saved* registers are modified by the current 146 // function, thus needing to be saved and restored in the prolog/epilog. 147 // 148 const bool *PhysRegsUsed = Fn.getUsedPhysregs(); 149 const TargetRegisterClass* const *CSRegClasses = 150 RegInfo->getCalleeSaveRegClasses(); 151 std::vector<CalleeSavedInfo> CSI; 152 for (unsigned i = 0; CSRegs[i]; ++i) { 153 unsigned Reg = CSRegs[i]; 154 if (PhysRegsUsed[Reg]) { 155 // If the reg is modified, save it! 156 CSI.push_back(CalleeSavedInfo(Reg, CSRegClasses[i])); 157 } else { 158 for (const unsigned *AliasSet = RegInfo->getAliasSet(Reg); 159 *AliasSet; ++AliasSet) { // Check alias registers too. 160 if (PhysRegsUsed[*AliasSet]) { 161 CSI.push_back(CalleeSavedInfo(Reg, CSRegClasses[i])); 162 break; 163 } 164 } 165 } 166 } 167 168 if (CSI.empty()) 169 return; // Early exit if no callee saved registers are modified! 170 171 unsigned NumFixedSpillSlots; 172 const std::pair<unsigned,int> *FixedSpillSlots = 173 TFI->getCalleeSaveSpillSlots(NumFixedSpillSlots); 174 175 // Now that we know which registers need to be saved and restored, allocate 176 // stack slots for them. 177 MinCSFrameIndex = INT_MAX; 178 MaxCSFrameIndex = 0; 179 for (unsigned i = 0, e = CSI.size(); i != e; ++i) { 180 unsigned Reg = CSI[i].getReg(); 181 const TargetRegisterClass *RC = CSI[i].getRegClass(); 182 183 // Check to see if this physreg must be spilled to a particular stack slot 184 // on this target. 185 const std::pair<unsigned,int> *FixedSlot = FixedSpillSlots; 186 while (FixedSlot != FixedSpillSlots+NumFixedSpillSlots && 187 FixedSlot->first != Reg) 188 ++FixedSlot; 189 190 int FrameIdx; 191 if (FixedSlot == FixedSpillSlots+NumFixedSpillSlots) { 192 // Nope, just spill it anywhere convenient. 193 FrameIdx = FFI->CreateStackObject(RC->getSize(), RC->getAlignment()); 194 if ((unsigned)FrameIdx < MinCSFrameIndex) MinCSFrameIndex = FrameIdx; 195 if ((unsigned)FrameIdx > MaxCSFrameIndex) MaxCSFrameIndex = FrameIdx; 196 } else { 197 // Spill it to the stack where we must. 198 FrameIdx = FFI->CreateFixedObject(RC->getSize(), FixedSlot->second); 199 } 200 CSI[i].setFrameIdx(FrameIdx); 201 } 202 203 FFI->setCalleeSavedInfo(CSI); 204} 205 206/// saveCalleeSavedRegisters - Insert spill code for any callee saved registers 207/// that are modified in the function. 208/// 209void PEI::saveCalleeSavedRegisters(MachineFunction &Fn) { 210 // Get callee saved register information. 211 MachineFrameInfo *FFI = Fn.getFrameInfo(); 212 const std::vector<CalleeSavedInfo> &CSI = FFI->getCalleeSavedInfo(); 213 214 // Early exit if no callee saved registers are modified! 215 if (CSI.empty()) 216 return; 217 218 const MRegisterInfo *RegInfo = Fn.getTarget().getRegisterInfo(); 219 220 // Now that we have a stack slot for each register to be saved, insert spill 221 // code into the entry block. 222 MachineBasicBlock *MBB = Fn.begin(); 223 MachineBasicBlock::iterator I = MBB->begin(); 224 for (unsigned i = 0, e = CSI.size(); i != e; ++i) { 225 // Insert the spill to the stack frame. 226 RegInfo->storeRegToStackSlot(*MBB, I, CSI[i].getReg(), CSI[i].getFrameIdx(), 227 CSI[i].getRegClass()); 228 } 229 230 // Add code to restore the callee-save registers in each exiting block. 231 const TargetInstrInfo &TII = *Fn.getTarget().getInstrInfo(); 232 for (MachineFunction::iterator FI = Fn.begin(), E = Fn.end(); FI != E; ++FI) 233 // If last instruction is a return instruction, add an epilogue. 234 if (!FI->empty() && TII.isReturn(FI->back().getOpcode())) { 235 MBB = FI; 236 I = MBB->end(); --I; 237 238 // Skip over all terminator instructions, which are part of the return 239 // sequence. 240 MachineBasicBlock::iterator I2 = I; 241 while (I2 != MBB->begin() && TII.isTerminatorInstr((--I2)->getOpcode())) 242 I = I2; 243 244 bool AtStart = I == MBB->begin(); 245 MachineBasicBlock::iterator BeforeI = I; 246 if (!AtStart) 247 --BeforeI; 248 249 // Restore all registers immediately before the return and any terminators 250 // that preceed it. 251 for (unsigned i = 0, e = CSI.size(); i != e; ++i) { 252 RegInfo->loadRegFromStackSlot(*MBB, I, CSI[i].getReg(), 253 CSI[i].getFrameIdx(), 254 CSI[i].getRegClass()); 255 assert(I != MBB->begin() && 256 "loadRegFromStackSlot didn't insert any code!"); 257 // Insert in reverse order. loadRegFromStackSlot can insert multiple 258 // instructions. 259 if (AtStart) 260 I = MBB->begin(); 261 else { 262 I = BeforeI; 263 ++I; 264 } 265 } 266 } 267} 268 269 270/// calculateFrameObjectOffsets - Calculate actual frame offsets for all of the 271/// abstract stack objects. 272/// 273void PEI::calculateFrameObjectOffsets(MachineFunction &Fn) { 274 const TargetFrameInfo &TFI = *Fn.getTarget().getFrameInfo(); 275 276 bool StackGrowsDown = 277 TFI.getStackGrowthDirection() == TargetFrameInfo::StackGrowsDown; 278 279 // Loop over all of the stack objects, assigning sequential addresses... 280 MachineFrameInfo *FFI = Fn.getFrameInfo(); 281 282 unsigned StackAlignment = TFI.getStackAlignment(); 283 unsigned MaxAlign = 0; 284 285 // Start at the beginning of the local area. 286 // The Offset is the distance from the stack top in the direction 287 // of stack growth -- so it's always positive. 288 int Offset = TFI.getOffsetOfLocalArea(); 289 if (StackGrowsDown) 290 Offset = -Offset; 291 assert(Offset >= 0 292 && "Local area offset should be in direction of stack growth"); 293 294 // If there are fixed sized objects that are preallocated in the local area, 295 // non-fixed objects can't be allocated right at the start of local area. 296 // We currently don't support filling in holes in between fixed sized objects, 297 // so we adjust 'Offset' to point to the end of last fixed sized 298 // preallocated object. 299 for (int i = FFI->getObjectIndexBegin(); i != 0; ++i) { 300 int FixedOff; 301 if (StackGrowsDown) { 302 // The maximum distance from the stack pointer is at lower address of 303 // the object -- which is given by offset. For down growing stack 304 // the offset is negative, so we negate the offset to get the distance. 305 FixedOff = -FFI->getObjectOffset(i); 306 } else { 307 // The maximum distance from the start pointer is at the upper 308 // address of the object. 309 FixedOff = FFI->getObjectOffset(i) + FFI->getObjectSize(i); 310 } 311 if (FixedOff > Offset) Offset = FixedOff; 312 } 313 314 // First assign frame offsets to stack objects that are used to spill 315 // callee save registers. 316 if (StackGrowsDown) { 317 for (unsigned i = 0, e = FFI->getObjectIndexEnd(); i != e; ++i) { 318 if (i < MinCSFrameIndex || i > MaxCSFrameIndex) 319 continue; 320 321 // If stack grows down, we need to add size of find the lowest 322 // address of the object. 323 Offset += FFI->getObjectSize(i); 324 325 unsigned Align = FFI->getObjectAlignment(i); 326 // If the alignment of this object is greater than that of the stack, then 327 // increase the stack alignment to match. 328 MaxAlign = std::max(MaxAlign, Align); 329 // Adjust to alignment boundary 330 Offset = (Offset+Align-1)/Align*Align; 331 332 FFI->setObjectOffset(i, -Offset); // Set the computed offset 333 } 334 } else { 335 for (int i = FFI->getObjectIndexEnd()-1; i >= 0; --i) { 336 if ((unsigned)i < MinCSFrameIndex || (unsigned)i > MaxCSFrameIndex) 337 continue; 338 339 unsigned Align = FFI->getObjectAlignment(i); 340 // If the alignment of this object is greater than that of the stack, then 341 // increase the stack alignment to match. 342 MaxAlign = std::max(MaxAlign, Align); 343 // Adjust to alignment boundary 344 Offset = (Offset+Align-1)/Align*Align; 345 346 FFI->setObjectOffset(i, Offset); 347 Offset += FFI->getObjectSize(i); 348 } 349 } 350 351 // Then assign frame offsets to stack objects that are not used to spill 352 // callee save registers. 353 for (unsigned i = 0, e = FFI->getObjectIndexEnd(); i != e; ++i) { 354 if (i >= MinCSFrameIndex && i <= MaxCSFrameIndex) 355 continue; 356 357 // If stack grows down, we need to add size of find the lowest 358 // address of the object. 359 if (StackGrowsDown) 360 Offset += FFI->getObjectSize(i); 361 362 unsigned Align = FFI->getObjectAlignment(i); 363 // If the alignment of this object is greater than that of the stack, then 364 // increase the stack alignment to match. 365 MaxAlign = std::max(MaxAlign, Align); 366 // Adjust to alignment boundary 367 Offset = (Offset+Align-1)/Align*Align; 368 369 if (StackGrowsDown) { 370 FFI->setObjectOffset(i, -Offset); // Set the computed offset 371 } else { 372 FFI->setObjectOffset(i, Offset); 373 Offset += FFI->getObjectSize(i); 374 } 375 } 376 377 378 // Align the final stack pointer offset, but only if there are calls in the 379 // function. This ensures that any calls to subroutines have their stack 380 // frames suitable aligned. 381 if (FFI->hasCalls()) 382 Offset = (Offset+StackAlignment-1)/StackAlignment*StackAlignment; 383 384 // Set the final value of the stack pointer... 385 FFI->setStackSize(Offset+TFI.getOffsetOfLocalArea()); 386 387 // Remember the required stack alignment in case targets need it to perform 388 // dynamic stack alignment. 389 assert(FFI->getMaxAlignment() == MaxAlign && 390 "Stack alignment calculation broken!"); 391} 392 393 394/// insertPrologEpilogCode - Scan the function for modified callee saved 395/// registers, insert spill code for these callee saved registers, then add 396/// prolog and epilog code to the function. 397/// 398void PEI::insertPrologEpilogCode(MachineFunction &Fn) { 399 // Add prologue to the function... 400 Fn.getTarget().getRegisterInfo()->emitPrologue(Fn); 401 402 // Add epilogue to restore the callee-save registers in each exiting block 403 const TargetInstrInfo &TII = *Fn.getTarget().getInstrInfo(); 404 for (MachineFunction::iterator I = Fn.begin(), E = Fn.end(); I != E; ++I) { 405 // If last instruction is a return instruction, add an epilogue 406 if (!I->empty() && TII.isReturn(I->back().getOpcode())) 407 Fn.getTarget().getRegisterInfo()->emitEpilogue(Fn, *I); 408 } 409} 410 411 412/// replaceFrameIndices - Replace all MO_FrameIndex operands with physical 413/// register references and actual offsets. 414/// 415void PEI::replaceFrameIndices(MachineFunction &Fn) { 416 if (!Fn.getFrameInfo()->hasStackObjects()) return; // Nothing to do? 417 418 const TargetMachine &TM = Fn.getTarget(); 419 assert(TM.getRegisterInfo() && "TM::getRegisterInfo() must be implemented!"); 420 const MRegisterInfo &MRI = *TM.getRegisterInfo(); 421 422 for (MachineFunction::iterator BB = Fn.begin(), E = Fn.end(); BB != E; ++BB) 423 for (MachineBasicBlock::iterator I = BB->begin(); I != BB->end(); ++I) 424 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) 425 if (I->getOperand(i).isFrameIndex()) { 426 // If this instruction has a FrameIndex operand, we need to use that 427 // target machine register info object to eliminate it. 428 MRI.eliminateFrameIndex(I); 429 break; 430 } 431} 432