PrologEpilogInserter.cpp revision 692d4e0823774730b90e8e2d7bf58119397f0535
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" 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 callee saved registers and insert spill 47 // code for any callee 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 calculateCalleeSavedRegisters(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, calculateCalleeSavedRegisters 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 calculateCalleeSavedRegisters(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/// calculateCalleeSavedRegisters - 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::calculateCalleeSavedRegisters(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; 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 FFI->setCalleeSavedInfo(CSI); 191} 192 193/// saveCallerSavedRegisters - Insert spill code for any caller saved registers 194/// that are modified in the function. 195/// 196void PEI::saveCallerSavedRegisters(MachineFunction &Fn) { 197 // Get callee saved register information. 198 MachineFrameInfo *FFI = Fn.getFrameInfo(); 199 const std::vector<CalleeSavedInfo> &CSI = FFI->getCalleeSavedInfo(); 200 201 // Early exit if no caller saved registers are modified! 202 if (CSI.empty()) 203 return; 204 205 const MRegisterInfo *RegInfo = Fn.getTarget().getRegisterInfo(); 206 207 // Now that we have a stack slot for each register to be saved, insert spill 208 // code into the entry block. 209 MachineBasicBlock *MBB = Fn.begin(); 210 MachineBasicBlock::iterator I = MBB->begin(); 211 for (unsigned i = 0, e = CSI.size(); i != e; ++i) { 212 // Insert the spill to the stack frame. 213 RegInfo->storeRegToStackSlot(*MBB, I, CSI[i].getReg(), CSI[i].getFrameIdx(), 214 CSI[i].getRegClass()); 215 } 216 217 // Add code to restore the callee-save registers in each exiting block. 218 const TargetInstrInfo &TII = *Fn.getTarget().getInstrInfo(); 219 for (MachineFunction::iterator FI = Fn.begin(), E = Fn.end(); FI != E; ++FI) 220 // If last instruction is a return instruction, add an epilogue. 221 if (!FI->empty() && TII.isReturn(FI->back().getOpcode())) { 222 MBB = FI; 223 I = MBB->end(); --I; 224 225 // Skip over all terminator instructions, which are part of the return 226 // sequence. 227 MachineBasicBlock::iterator I2 = I; 228 while (I2 != MBB->begin() && TII.isTerminatorInstr((--I2)->getOpcode())) 229 I = I2; 230 231 bool AtStart = I == MBB->begin(); 232 MachineBasicBlock::iterator BeforeI = I; 233 if (!AtStart) 234 --BeforeI; 235 236 // Restore all registers immediately before the return and any terminators 237 // that preceed it. 238 for (unsigned i = 0, e = CSI.size(); i != e; ++i) { 239 RegInfo->loadRegFromStackSlot(*MBB, I, CSI[i].getReg(), 240 CSI[i].getFrameIdx(), 241 CSI[i].getRegClass()); 242 assert(I != MBB->begin() && 243 "loadRegFromStackSlot didn't insert any code!"); 244 // Insert in reverse order. loadRegFromStackSlot can insert multiple 245 // instructions. 246 if (AtStart) 247 I = MBB->begin(); 248 else { 249 I = BeforeI; 250 ++I; 251 } 252 } 253 } 254} 255 256 257/// calculateFrameObjectOffsets - Calculate actual frame offsets for all of the 258/// abstract stack objects. 259/// 260void PEI::calculateFrameObjectOffsets(MachineFunction &Fn) { 261 const TargetFrameInfo &TFI = *Fn.getTarget().getFrameInfo(); 262 263 bool StackGrowsDown = 264 TFI.getStackGrowthDirection() == TargetFrameInfo::StackGrowsDown; 265 266 // Loop over all of the stack objects, assigning sequential addresses... 267 MachineFrameInfo *FFI = Fn.getFrameInfo(); 268 269 unsigned StackAlignment = TFI.getStackAlignment(); 270 unsigned MaxAlign = 0; 271 272 // Start at the beginning of the local area. 273 // The Offset is the distance from the stack top in the direction 274 // of stack growth -- so it's always positive. 275 int Offset = TFI.getOffsetOfLocalArea(); 276 if (StackGrowsDown) 277 Offset = -Offset; 278 assert(Offset >= 0 279 && "Local area offset should be in direction of stack growth"); 280 281 // If there are fixed sized objects that are preallocated in the local area, 282 // non-fixed objects can't be allocated right at the start of local area. 283 // We currently don't support filling in holes in between fixed sized objects, 284 // so we adjust 'Offset' to point to the end of last fixed sized 285 // preallocated object. 286 for (int i = FFI->getObjectIndexBegin(); i != 0; ++i) { 287 int FixedOff; 288 if (StackGrowsDown) { 289 // The maximum distance from the stack pointer is at lower address of 290 // the object -- which is given by offset. For down growing stack 291 // the offset is negative, so we negate the offset to get the distance. 292 FixedOff = -FFI->getObjectOffset(i); 293 } else { 294 // The maximum distance from the start pointer is at the upper 295 // address of the object. 296 FixedOff = FFI->getObjectOffset(i) + FFI->getObjectSize(i); 297 } 298 if (FixedOff > Offset) Offset = FixedOff; 299 } 300 301 for (unsigned i = 0, e = FFI->getObjectIndexEnd(); i != e; ++i) { 302 // If stack grows down, we need to add size of find the lowest 303 // address of the object. 304 if (StackGrowsDown) 305 Offset += FFI->getObjectSize(i); 306 307 unsigned Align = FFI->getObjectAlignment(i); 308 // If the alignment of this object is greater than that of the stack, then 309 // increase the stack alignment to match. 310 MaxAlign = std::max(MaxAlign, Align); 311 // Adjust to alignment boundary 312 Offset = (Offset+Align-1)/Align*Align; 313 314 if (StackGrowsDown) { 315 FFI->setObjectOffset(i, -Offset); // Set the computed offset 316 } else { 317 FFI->setObjectOffset(i, Offset); 318 Offset += FFI->getObjectSize(i); 319 } 320 } 321 322 // Align the final stack pointer offset, but only if there are calls in the 323 // function. This ensures that any calls to subroutines have their stack 324 // frames suitable aligned. 325 if (FFI->hasCalls()) 326 Offset = (Offset+StackAlignment-1)/StackAlignment*StackAlignment; 327 328 // Set the final value of the stack pointer... 329 FFI->setStackSize(Offset+TFI.getOffsetOfLocalArea()); 330 331 // Remember the required stack alignment in case targets need it to perform 332 // dynamic stack alignment. 333 assert(FFI->getMaxAlignment() == MaxAlign && 334 "Stack alignment calculation broken!"); 335} 336 337 338/// insertPrologEpilogCode - Scan the function for modified caller saved 339/// registers, insert spill code for these caller saved registers, then add 340/// prolog and epilog code to the function. 341/// 342void PEI::insertPrologEpilogCode(MachineFunction &Fn) { 343 // Add prologue to the function... 344 Fn.getTarget().getRegisterInfo()->emitPrologue(Fn); 345 346 // Add epilogue to restore the callee-save registers in each exiting block 347 const TargetInstrInfo &TII = *Fn.getTarget().getInstrInfo(); 348 for (MachineFunction::iterator I = Fn.begin(), E = Fn.end(); I != E; ++I) { 349 // If last instruction is a return instruction, add an epilogue 350 if (!I->empty() && TII.isReturn(I->back().getOpcode())) 351 Fn.getTarget().getRegisterInfo()->emitEpilogue(Fn, *I); 352 } 353} 354 355 356/// replaceFrameIndices - Replace all MO_FrameIndex operands with physical 357/// register references and actual offsets. 358/// 359void PEI::replaceFrameIndices(MachineFunction &Fn) { 360 if (!Fn.getFrameInfo()->hasStackObjects()) return; // Nothing to do? 361 362 const TargetMachine &TM = Fn.getTarget(); 363 assert(TM.getRegisterInfo() && "TM::getRegisterInfo() must be implemented!"); 364 const MRegisterInfo &MRI = *TM.getRegisterInfo(); 365 366 for (MachineFunction::iterator BB = Fn.begin(), E = Fn.end(); BB != E; ++BB) 367 for (MachineBasicBlock::iterator I = BB->begin(); I != BB->end(); ++I) 368 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) 369 if (I->getOperand(i).isFrameIndex()) { 370 // If this instruction has a FrameIndex operand, we need to use that 371 // target machine register info object to eliminate it. 372 MRI.eliminateFrameIndex(I); 373 break; 374 } 375} 376